29. Arshad, M; Biswas, K; Bisgrove, S; Schroeder, WR; Thomas, BR; Mansfield, SD; Mattsson, J; Plant, A. (2019) Differences in drought resistance in nine North American hybrid poplars.Trees-Struct. Funct. 33: 1111-1128 Differences in drought resistance in nine North American hybrid poplars
Populus; Physiology; Gene expression; ABA; Ranking; Indicator gene
Poplar hybrids are cultivated in North America for environmental applications, agroforestry, and the pulp and paper industry primarily because of their fast growth and limited nutrient requirement. For the same reasons, they have been identified as suitable species for carbon sequestration and as a potential feedstock for carbon-neutral production of energy. The clones deployed on the Canadian prairies are generally regarded as drought sensitive, which poses a problem as water availability has steadily decreased in this region over the past century and a severe water crisis has been predicted. To approach this problem, we tested nine commonly deployed North-American hybrid poplars, developed for large-scale cultivation in the Canadian prairies, for their physiological responses to drought, resulting in a ranking of drought resistance. The difference between the clones showing the most and the least response of drought stress was large, and we used these clones to further examine the differences in the expression of genes known to be up-regulated in response to drought stress. This interrogation showed significant differences in transcript abundance that largely reflected the physiological status of the tested clones, but also many genes being down rather than up-regulated in response to drought stress in the drought-tolerant clone. In particular, putative positive and negative regulators of abscisic acid signaling were expressed at levels consistent with a potential role in observed differences in drought resistance. DOI
28. Schiltroth, BWJ; Ohori, KT; Bisgrove, SR. (2019) Impacts of Acidic Seawater on Early Developmental Stages of Fucus gardneri at Burrard Inlet, British Columbia.Front. Mar. Sci. 6 Impacts of Acidic Seawater on Early Developmental Stages of Fucus gardneri at Burrard Inlet, British Columbia
ocean acidification; fucoid algae; rhizoid elongation (tip growth); effects of climate change; algal development
Increases in stressors associated with climate change such as ocean acidification and warming temperatures pose a serious threat to intertidal ecosystems. Of crucial importance are the effects on foundational species, such as fucoid algae, a critical component of rocky intertidal shorelines around the world. The impact of climate change on adult fronds of fucoid algae has been documented but effects on early developmental stages are not as well understood. In particular, ocean acidification stands to impact these stages because zygotes and embryos are known to maintain internal pH and develop a cytosolic pH gradient during development. To assess the effects of seawater acidification on early development, zygotes of Fucus gardneri were exposed to artificial seawater (ASW) buffered to conditions that approximate current global averages and extend largely beyond future projections. Exposure to acidic seawater had significant effects on embryonic growth. Specifically, rhizoid elongation, which occurs by a process known as tip growth, was significantly reduced with each 0.5 unit drop in pH. When pH was decreased from 8.0 to 7.5, which is similar to levels that have been observed in Burrard Inlet, there was reduction in rhizoid growth rate of almost 20%. Under more extreme conditions, at pH 6, rhizoid growth rates were reduced by 64% in comparison to embryos exposed to seawater at pH 8.0. On the other hand, acidic seawater had no effect on earlier processes; zygotes became multicellular embryos with well-formed rhizoids on a similar time course within the first 24 h of development, even when exposed to pH 6, an extreme pH well below what is expected in the future. This suggests that zygotes can maintain an internal pH that allows germination and cell division to occur. Tip growth, however, depends on the extended maintenance of an internal pH gradient. It is therefore possible that disruptions to this gradient could account for the observed reductions in rhizoid elongation. Under acidic conditions proton influx into the cell becomes energetically more favorable than at pH 8, and expulsion would be more difficult. This could disrupt the cytosolic pH gradient and in turn affect rhizoid growth. DOI
27. Squires, S and Bisgrove, S. (2013) The Microtubule-Associated Protein END BINDING1b, Auxin, and Root Responses to Mechanical Cues.Journal of Plant Growth Regulation 32: 681-691 The Microtubule-Associated Protein END BINDING1b, Auxin, and Root Responses to Mechanical Cues
The ability of roots to penetrate through the soil
and maneuver around rocks and other impenetrable objects
requires a system for modulating output from mechanosensory
response networks. The microtubule-associated protein END BINDING1b (EB1b) has a role in this process; it represses root responses to mechanical cues. In this study, a possible relationship between EB1b and auxin during root responses to mechanical cues was investigated. We found that eb1b-1-mutant roots are more sensitive than wild-type roots to chemicals that disrupt auxin transport, whereas the roots of mutants with defects in auxin transport are resistant to these treatments. Using seedlings that express the auxin-sensitive DR5rev::GFP construct, we also found that wild-type and eb1b-1 roots treated with the auxin transport inhibitor naphthylphthalamic acid exhibited dose-dependent reductions in basipetal auxin transport that were indistinguishable from each other. The responses of eb1b-1 roots to mechanical cues were also enhanced over wild type in the presence of p-chlorophenoxyisobutyric acid, a chemical thought to inhibit auxin signaling. Finally, roots of eb1b-1 and wild-type plants exhibited slight increases in loop formation in response to increasing levels of exogenously applied indole-3-acetic acid or 1-naphthalene acetic acid. Taken together, these results suggest that the repression of loop formation by EB1b and auxin transport/signaling occurs by different mechanisms.
26. Gleeson, L; Squires, S; Bisgrove, SR. (2012) The microtubule associated protein END BINDING 1 represses root responses to mechanical cues.Plant Science 187: 1-9 The microtubule associated protein END BINDING 1 represses root responses to mechanical cues
EB1; Touch response; Mechanoresponse; Thigmotropism; Gravitropism; Microtubule
The ability of roots to navigate around rocks and other debris as they grow through the soil requires a mechanism for detecting and responding to input from both touch and gravity sensing systems. The microtubule associated protein END BINDING 1b (EB1b) is involved in this process as mutants have defects responding to combinations of touch and gravity cues. This study investigates the role of EB1b in root responses to mechanical cues. We find that eb1b-1 mutant roots exhibit an increase over wild type in their response to touch and that the expression of EB1b genes in transgenic mutants restores the response to wild type levels, indicating that EB1b is an inhibitor of the response. Mutant roots are also hypersensitive to increased levels of mechanical stimulation, revealing the presence of another process that activates the response. These findings are supported by analyses of double mutants between eb1b-1 and seedlings carrying mutations in PHOSPHOGLUCOMUTASE (PGM), ALTERED RESPONSE TO GRAVITY1 (ARG1), or TOUCH3 (TCH3), genes that encode proteins involved in gravity sensing, signaling, or touch responses, respectively. A model is proposed in which root responses to mechanical cues are modulated by at least two competing regulatory processes, one that promotes touch-mediated growth and another, regulated by EB1b, which dampens root responses to touch and enhances gravitropism. Crown Copyright (C) 2012 Published by Elsevier Ireland Ltd. All rights reserved. DOI
22.Bisgrove, SR. (2008) The roles of microtubules in tropisms.Plant Science 175: 747-755 The roles of microtubules in tropisms
Microtubule; Cytoskeleton; Cell expansion; Cell wall; Tropism
Plant tropisms, or growth towards or away from a stimulus, usually involve the bending of shoots or roots which reorient growth in a new direction. Plant responses to tropic cues, especially gravity and light, have been active areas of investigation for many years. Despite all of this attention we still do not understand how these responses are regulated. In this review possible roles for microtubules in tropisms are discussed. Tropisms occur in a series of steps; directional cues are perceived and converted into biochemical signals that induce bending in roots and shoots. One model suggests that microtubules function late in the response pathway, during organ bending. Microtubules have been linked to organ bending by virtue of their role in regulating the direction of cell elongation. In elongating cells microtubules appear to function as guides for the deposition of cellulose microfibrils into the cell wall and the placement of the microfibrils in the wall is thought to constrain the direction of cell elongation. According to the model bending occurs when different microtubule/microfibril alignments across the organ cause cells on the outer flank to elongate more than cells on the inner flank. In support of this idea is the observation that tropic signals can induce the appropriate changes in microtubule orientations across a bending organ. However, attempts to validate the hypothesis have produced conflicting results and the idea that microtubule alignment regulates cell expansion during organ bending is controversial. Microtubules have also been linked to organizational events associated with the plasma membrane. Although speculative, one possibility is that microtubules influence tropisms by positioning regulatory proteins and/or complexes in the plasma membrane. Two possible mechanisms by which microtubules could contribute to organizational events associated with the plasma membrane are outlined. In addition to cell expansion, microtubules are postulated to have roles in the perception of touch and gravity signals. Although microtubules are associated with touch sensing in animals, we know very little about the relevant receptors in plants. One way to assess how microtubules function during tropisms is to identify and study proteins that function in concert with microtubules. In particular, the analysis of microtubule-associated proteins whose mutant forms confer defects in tropic responses promises to provide additional insights into the roles of microtubules in tropisms. (c) 2008 Elsevier Ireland Ltd. All rights reserved. DOI
21.Bisgrove, SR; Lee, YRJ; Liu, B; Peters, NT; Kropf, DL. (2008) The microtubule plus-end binding protein EB1 functions in root responses to touch and gravity signals in Arabidopsis.Plant Cell 20: 396-410 The microtubule plus-end binding protein EB1 functions in root responses to touch and gravity signals in Arabidopsis
Microtubules function in concert with associated proteins that modify microtubule behavior and/or transmit signals that effect changes in growth. To better understand how microtubules and their associated proteins influence growth, we analyzed one family of microtubule-associated proteins, the END BINDING1 (EB1) proteins, in Arabidopsis thaliana (EB1a, EB1b, and EB1c). We find that antibodies directed against EB1 proteins colocalize with microtubules in roots, an observation that confirms previous reports using EB1-GFP fusions. We also find that T-DNA insertion mutants with reduced expression from EB1 genes have roots that deviate toward the left on vertical or inclined plates. Mutant roots also exhibit extended horizontal growth before they bend downward after tracking around an obstacle or after a 908 clockwise reorientation of the root. These observations suggest that leftward deviations in root growth may be the result of delayed responses to touch and/or gravity signals. Root lengths and widths are normal, indicating that the delay in bend formation is not due to changes in the overall rate of growth. In addition, the genotype with the most severe defects responds to low doses of microtubule inhibitors in a manner indistinguishable from the wild type, indicating that microtubule integrity is not a major contributor to the leftward deviations in mutant root growth. DOI
20.Bisgrove, SR. (2007) Cytoskeleton and early development in fucoid algae.Journal of Integrative Plant Biology 49: 1192-1198 Cytoskeleton and early development in fucoid algae
actin; asymmetric cell division; cell polarization; cytoskeleton; early development; fucoid algae; microtubules; zygote
Cell polarization and asymmetric cell divisions play important roles during development in many multicellular eukaryotes. Fucoid algae have a long history as models for studying early developmental processes, probably because of the ease with which zygotes can be observed and manipulated in the laboratory. This review discusses cell polarization and asymmetric cell divisions in fucoid algal zygotes with an emphasis on the roles played by the cytoskeleton.PDF DOI
19.Bisgrove, SR; Kropf, DL. (2007) Asymmetric cell divisions: Zygotes of Fucoid Algae as a Model System.In Cell Division Control in Plants, Plant Cell Monographs, Vol. 9, Pp. 323-341, D.P.S. Verma and Z. Hong, Eds., Springer-Verlag, Heidelberg.Asymmetric cell divisions: Zygotes of Fucoid Algae as a Model System
Asymmetric cell divisions are commonly used across diverse phyla to generate
different kinds of cells during development. Although asymmetric divisions play import-
ant roles during development in plants, algae, fungi, and animals, emerging data indicate
that there is some variability amongst the mechanisms that are at play in these differ-
ent organisms. Zygotes of fucoid algae have long served as models for understanding
early developmental processes including cell polarization and asymmetric cell division. In
addition, brown algae are phylogenetically distant from other organisms, including plant
models, a feature that makes them interesting from a comparative perspective (Andersen
2004; Peters et al. 2004). This monograph focuses on advances made toward under-
standing how asymmetric divisions are regulated in fucoid algae and, where appropriate,
comparisons are made to higher plant zygotes.
PDF DOI
17.Bisgrove, SR; Kropf, DL. (2004) Cytokinesis in brown algae: studies of asymmetric division in fucoid zygotes.Protoplasma 223: 163-173 Cytokinesis in brown algae: studies of asymmetric division in fucoid zygotes
Silvetia compressa; Pelvetia compressa; microtubule; actin; secretion
The mechanism of cytokinesis was investigated during the first asymmetric division in fucoid zygotes. A plate of actin assembled midway between daughter nuclei where microtubules interdigitated and defined the cytokinetic plane. A membrane was then deposited in islands throughout the cytokinetic plane: the islands eventually fused into a continuous partition membrane and cell plate material was deposited in the intermembrane space. All of these structures matured from the center of the cell outward (centrifugal maturation). Pharmacological agents were used to investigate the roles of microtubules, actin, and secretion in cytokinesis. The findings indicate a mechanism of cytokinesis that may be unique to the brown algae. DOI
16.Bisgrove, SR; Henderson, DC; Kropf, DL. (2003) Asymmetric division in fucoid zygotes is positioned by telophase nuclei.Plant Cell 15: 854-862 Asymmetric division in fucoid zygotes is positioned by telophase nuclei
The relative contributions of cell polarity and nuclear position in specifying the plane of asymmetric division in fucoid zygotes were investigated. In zygotes developing normally, telophase nuclei were positioned parallel to the polar growth axis, and the division plane bisected both axes. To assess division plane specification, the colinearity of the nuclear and growth axes was uncoupled by treatment with pharmacological agents. Spatial correlations between the growth axis, telophase nuclei, and the division plane were analyzed in the treated zygotes. In all cases, cytokinesis was oriented transverse to the telophase mitotic array and was less well aligned with the growth axis. Telophase nuclei also played a predominant role in positioning the division plane in polyspermic zygotes. Microtubules from the telophase nuclei interdigitated throughout the plane of subsequent cytokinesis, and we speculate that they specify the division plane. Morphological markers of the division plane were not observed before telophase; the earliest division marker detected was a plate of actin that assembled in the zone of microtubule overlap late in telophase. These findings are consistent with division plane specification at cytoplast boundaries. DOI
15.Bisgrove, SR; Kropf, DL. (2001) Asymmetric cell division in fucoid algae: a role for cortical adhesions in alignment of the mitotic apparatus.Journal of Cell Science 114: 4319-4328 Asymmetric cell division in fucoid algae: a role for cortical adhesions in alignment of the mitotic apparatus
adhesions; asymmetric cell division; brown algae; spindle alignment
The first cell division in zygotes of the fucoid brown alga Pelvetia compressa is asymmetric and we are interested in the mechanism controlling the alignment of this division. Since the division plane bisects the mitotic apparatus, we investigated the timing and mechanism of spindle alignments. Centrosomes, which give rise to spindle poles, aligned with the growth axis in two phases - a premetaphase rotation of the nucleus and centrosomes followed by a postmetaphase alignment that coincided with the separation of the mitotic spindle poles during anaphase and telophase. The roles of the cytoskeleton and cell cortex in the two phases of alignment were analyzed by treatment with pharmacological agents. Treatments that disrupted cytoskeleton or perturbed cortical adhesions inhibited premetaphase alignment and we propose that this rotational alignment is effected by microtubules anchored at cortical adhesion sites. Postmetaphase alignment was not affected by any of the treatments tested, and may be dependent on asymmetric cell morphology.
14.Bisgrove, SR; Kropf, DL. (2001) Cell wall deposition during morphogenesis in fucoid algae.Planta 212: 648-658 Cell wall deposition during morphogenesis in fucoid algae
brown algae; cellulose; cell wall; cytoskeleton; Pelvetia (tip growth); tip growth
Cell wall deposition was investigated during morphogenesis in zygotes of Pelvetia compressa (J. Agardh) De Toni. Young zygotes are spherical and wall is deposited uniformly, but at germination (about 10 h after fertilization) wall deposition becomes localized to the apex of the tip-growing rhizoid. Wall deposition was investigated before and after the initiation of tip growth by disrupting cytoskeleton, secretion or cellulose deposition; effects on wall strength and structure were examined. All three were involved in generating wall strength in both spherical and tip-growing zygotes, but their relative importance were different at the two developmental stages. Much of the wall strength in young zygotes was dependent on F-actin, whereas cellulose and a sulfated component, probably a fucan (F2), were most important in tip growing zygotes. Some treatments had contrasting effects at the two developmental stages: for example, disruption of F-actin or inhibition of secretion weakened walls in spherical zygotes but strengthened those in tip-growing zygotes. Transmission electron microscopic analysis showed that most treatments that altered wall strength induced modifications of internal wall structure. DOI
13. Corellou, F; Bisgrove, SR; Kropf, DL; Meijer, L; Kloareg, B; Bouget, FY. (2000) A S/M DNA replication checkpoint prevents nuclear and cytoplasmic events of cell division including centrosomal axis alignment and inhibits activation of cyclin-dependent kinase-like proteins in fucoid zygotes.Development 127: 1651-1660 A S/M DNA replication checkpoint prevents nuclear and cytoplasmic events of cell division including centrosomal axis alignment and inhibits activation of cyclin-dependent kinase-like proteins in fucoid zygotes
fucoid zygote; S/M checkpoint; aphidicolin; centrosomes; CDK; cdc25; olomoucine
S/M checkpoints prevent various aspects of cell division when DNA has not been replicated. Such checkpoints are stringent in yeast and animal somatic cells but are usually partial or not present in animal embryos, Because little is known about S/M checkpoints in plant cells and embryos, we have investigated the effect of aphidicolin, a specific inhibitor of DNA polymerases alpha and delta, on cell division and morphogenesis in Fucus and Pelvetia zygotes, Both DNA replication and cell division were inhibited by aphidicolin, indicating the presence, in fucoid zygotes, of a S/M checkpoint. This checkpoint prevents chromatin condensation, spindle formation, centrosomal alignment with the growth axis and cytokinesis but has no effect on germination or rhizoid elongation. This S/M checkpoint also prevents tyrosine dephosphorylation of cyclin-dependent kinase-like proteins at the onset of mitosis, The kinase activity is restored in extracts upon incubation with cdc25A phosphatase, When added in S phase, olomoucine, a specific inhibitor of cyclin-dependent kinases, has similar effects as aphidicolin on cell division although alignment of the centrosomal axis still occurs. We propose a model involving the inactivation of CDK-like proteins to account for the S/M DNA replication checkpoint in fucoid zygotes and embryos.
12. Kropf, DL; Bisgrove, SR; Hable, WE. (1999) Establishing a growth axis in fucoid algae.Trends in Plant Science 4: 490-494 Establishing a growth axis in fucoid algae
Recent studies indicate that fucoid zygotes establish developmental polarity much earlier than previously thought, A growth axis is first set in place at fertilization, with the site of sperm entry defining the rhizoid pole of the axis, This initial axis is a default axis, which is only used as the final growth axis if the zygote fails to detect spatial cues (such as sunlight) in its intertidal environment. However, the zygote usually senses vectorial information; it then abandons the sperm-induced axis and assembles a new axis de novo in accordance with the perceived vector(s). DOI
11.Bisgrove, SR; Kropf, DL. (1998) Alignment of centrosomal and growth axes is a late event during polarization of Pelvetia compressa zygotes.Developmental Biology 194: 246-256 Alignment of centrosomal and growth axes is a late event during polarization of Pelvetia compressa zygotes
Zygotes and embryos of the fucoid brown alga Pelvetia compressa undergo a series of asymmetric cleavages. We are interested in the developmental role of these cleavages and the mechanism controlling their alignment. To assess the importance of division plane alignment, the orientation of the first asymmetric division was altered and the effects on subsequent embryo elongation rates were analyzed. Although this division is normally oriented transversely (90 degrees) to the growth axis, deviations up to 45 degrees had no significant effects on embryo elongation. However, division planes that were parallel with the growth axis (0-45 degrees) had drastic effects. Embryo elongation was severely inhibited and the wall often bifurcated and avoided the rhizoid tip. The orientation of the division plane is determined by the position of the centrosomes. We therefore investigated centrosomal position and function during the first cell cycle within the three-dimensional context of the cell. We found that, after karyogamy, microtubule organization changed from a radially symmetric circumnuclear array into a bipolar centrosomal array. The reorganization coincided with the migration of the centrosomes around the nucleus. The centrosomes separated slowly and asynchronously until they reached opposite sides of the nuclear envelope. At this time the centrosomal axis, defined by the position of the two centrosomes, was oriented randomly with respect to the cortical growth axis. The centrosomal axis then rotated into alignment parallel with the growth axis late in the first cell cycle. These results indicate that the growth axis and the centrosomal axis develop independently of each other and that the centrosomal axis does not align with the growth axis until just prior to mitosis. (C) 1998 Academic Press. DOI
9. Henderson, DC; Bisgrove, SR; Hable, WE; Alessa, L; Kropf, DL. (1998) Division patterns in the thallus of Pelvetia compressa embryos and the effects of gravity.Protoplasma 203: 112-117 Division patterns in the thallus of Pelvetia compressa embryos and the effects of gravity
brown alga; cleavage plane; embryogenesis; gravity; microtubules; spindle orientation
The pattern of divisions in the thallus of Pelvetia compressa embryos was determined with respect to the embryonic growth axis. To detect all possible division planes, embryos were viewed from two vantages which permitted observations of (1) the thallus pole and (2) the longitudinal embryonic profile. Following formation of rhizoid and thallus cells by any asymmetrical division transverse to the embryonic axis that is established prior to any divisions, the thallus cell divided twice along the embryonic axis (axial divisions) in orthogonal planes, and then divided transverse to the growth axis. This division pattern produced an eight-cell thallus with four cells in each of two layers. The spatial relation between gravity and the first axial division was investigated, and gravity was found to have little effect on the alignment of this division. The reproducible pattern of divisions in the thallus indicates spatial control of spindle positioning. DOI
8. Kropf, DL; Bisgrove, SR; Hable, WE. (1998) Cytoskeletal control of polar growth in plant cells.Current Opinion in Cell Biology 10: 117-122 Cytoskeletal control of polar growth in plant cells
There are two quite different modes of polar cell expansion in plant cells, namely, diffuse growth and tip growth. The direction of diffuse growth is determined by the orientation of cellulose microfibrils in the cell wall, which in turn are aligned by microtubules in the cell cortex. The orientation of the cortical microtubule array changes in response to developmental and environmental signals, and recent evidence indicates that microtubule disassembly/reassembly and microtubule translocation participate in reorientation of the array. Tip growth, in contrast, is governed mainly by F-actin, which has several putative forms and functions in elongating cells. Longitudinal cables are involved in vesicle transport to the expanding apical dome and, in some tip growers, a subapical ring of F-actin may participate in wall-membrane adhesions. The structure and function of F-actin within the apical dome may be variable, ranging from a dense meshwork to sparse single filaments. The presence of multiple F-actin structures in elongating tips suggests extensive regulation of this cytoskeletal array. DOI
6.Bisgrove, SR; Nagasato, C; Motomura, T; Kropf, DL. (1997) Immunolocalization of centrin during fertilization and the first cell cycle in Fucus distichus and Pelvetia compressa (Fucales, Phaeophyceae).Journal of Phycology 33: 823-829 Immunolocalization of centrin during fertilization and the first cell cycle in Fucus distichus and Pelvetia compressa (Fucales, Phaeophyceae)
centrin; centrosomes; fertilization; division plane alignment; Pelvetia compressa; Fucus distichus subsp. evanescens
Antibodies that recognize the centrosome-associated protein centrin were used to characterize centrosomal origin and positioning during fertilization and the first cell cycle in Fucus distichus subsp. evanescens (C. Agardh) Powell and Pelvetia compressa (J. Agardh) Be Tent. Centrin was identified in sperm, eggs, and zygotes on protein blots, indicating the protein is present in both gametes. Using immunofluorescence microscopy, centrin was found in discrete foci in sperm. In contrast, eggs lack centrosomes and centrin was not detectable by immunofluorescence, indicating that centrin was probably dispersed in the cytoplasm. Two foci of centrin were present on the nuclear envelope of zygotes, but microtubules remained dispersed over the zygotic nucleus. Centrin foci separated over the nuclear envelope as the first cell cycle progressed. Microtubules became concentrated at the centrin foci to form centrosomes that gave rise to the spindle poles at mitosis. DOI
5. BISGROVE, SR; CROUCH, ML; FERNANDEZ, DE. (1995) CHIMERIC NATURE OF PRECOCIOUSLY-GERMINATING BRASSICA-NAPUS EMBRYOS - MESSENGER-RNA ACCUMULATION PATTERNS.Journal of Experimental Botany 46: 27-33 CHIMERIC NATURE OF PRECOCIOUSLY-GERMINATING BRASSICA-NAPUS EMBRYOS - MESSENGER-RNA ACCUMULATION PATTERNS
PRECOCIOUS GERMINATION; BRASSICA NAPUS; RAPESEED; EMBRYO DEVELOPMENT
During precocious germination, Brassica napus L. embryos exhibit features of embryo maturation and features of post-germinative growth at the same time, which raises important questions about the nature of these developmental programmes and the transition between them. To investigate the possibility that the two programmes are segregated spatially rather than temporally in these embryos, embryos of different ages (excised at 38, 47, and 60 d post-anthesis) were placed in culture to induce precocious germination, and total RNA was isolated from the cotyledons and axes or hypocotyls. cDNA sequences (two marking embryo maturation and four marking the onset of postgerminative growth) were used as probes on dot blots to compare mRNA population dynamics in these organs. We find that individual organs accumulate mRNAs characteristic of only one developmental programme at any given time and conclude that the programmes are both distinct and potentially mutually exclusive. Embryos are able to 'switch' from accumulating embryo maturation mRNAs to accumulating post-germinative mRNAs in culture, but the transition occurs at different times in different organs. DOI
4. BISGROVE, SR; SIMONICH, MT; SMITH, NM; SATTLER, A; INNES, RW. (1994) A DISEASE RESISTANCE GENE IN ARABIDOPSIS WITH SPECIFICITY FOR 2 DIFFERENT PATHOGEN AVIRULENCE GENES.Plant Cell 6: 927-933 A DISEASE RESISTANCE GENE IN ARABIDOPSIS WITH SPECIFICITY FOR 2 DIFFERENT PATHOGEN AVIRULENCE GENES
The RPS3 and RPM1 disease resistance loci of Arabidopsis confer resistance to Pseudomonas syringae strains that carry the avirulence genes avrB and avrRpm1, respectively. We have previously shown that RPS3 and RPM1 are closely linked genetically. Here, we show that RPS3 and RPM1 are in fact the same gene. We screened a mutagenized Arabidopsis population with a R syringae strain carrying avrB and found 12 susceptible mutants. All 12 mutants were also susceptible to an isogenic strain carrying avrRpm1, indicating a loss of both RPS3 and RPM1 functions. No mutants were recovered that lost only RPS3 function. Genetic analysis of four independent mutants revealed that the lesions were in RPS3 Thus, a single gene in Arabidopsis confers resistance that is specific to two distinct pathogen avirulence genes - a gene-for-genes interaction. This observation suggests that the RPS3/RPM1 gene product can bind multiple pathogen ligands, or alternatively, that it does not function as a receptor. DOI
2. INNES, RW; BENT, AF; KUNKEL, BN; BISGROVE, SR; STASKAWICZ, BJ. (1993) MOLECULAR ANALYSIS OF AVIRULENCE GENE AVRRPT2 AND IDENTIFICATION OF A PUTATIVE REGULATORY SEQUENCE COMMON TO ALL KNOWN PSEUDOMONAS-SYRINGAE AVIRULENCE GENES.Journal of Bacteriology 175: 4859-4869 MOLECULAR ANALYSIS OF AVIRULENCE GENE AVRRPT2 AND IDENTIFICATION OF A PUTATIVE REGULATORY SEQUENCE COMMON TO ALL KNOWN PSEUDOMONAS-SYRINGAE AVIRULENCE GENES
The avrRpt2 locus from Pseudomonas syringae pv. tomato causes virulent strains of P. syringae to be avirulent on some, but not all, lines of Arabidopsis thaliana and Glycine max (soybean). We determined the DNA sequence of the avrRpt2 locus and identified the avrRpt2 gene as a 768-bp open reading frame encoding a putative 28.2-kDa protein. Deletion analysis and transcription studies provided further evidence that this open reading frame encodes AvrRpt2. We found that the avrRpt2 gene also has avirulence activity in P. syringae pathogens of Phaseolus vulgaris (common bean), suggesting that disease resistance genes specific to avrRpt2 are functionally conserved among diverse plant species. The predicted AvrRpt2 protein is hydrophilic and contains no obvious membrane-spanning domains or export signal sequences, and there was no significant similarity of AvrRpt2 to sequences in the GenBank, EMBL, or Swiss PIR data bases. A comparison of the avrRpt2 DNA sequence to nine other P. syringae avirulence genes revealed a highly conserved sequence, GGAACCNA-N14-CCACNNA, upstream of the translation initiation codon. This motif is located 6 to 8 nucleotides upstream of the transcription start site in all four P. syringae avirulence genes for which a transcription start site has been determined, suggesting a role as a binding site for a novel form of RNA polymerase. Regulation of avrRpt2 was similar to other P. syringae avirulence genes; expression was high in minimal medium and low in rich medium and depended on the hrpRS locus and an additional locus at the opposite end of the hrp cluster of P. syringae pv. tomato.
1. INNES, RW; BISGROVE, SR; SMITH, NM; BENT, AF; STASKAWICZ, BJ; LIU, YC. (1993) IDENTIFICATION OF A DISEASE RESISTANCE LOCUS IN ARABIDOPSIS THAT IS FUNCTIONALLY HOMOLOGOUS TO THE RPG1 LOCUS OF SOYBEAN.Plant Journal 4: 813-820 IDENTIFICATION OF A DISEASE RESISTANCE LOCUS IN ARABIDOPSIS THAT IS FUNCTIONALLY HOMOLOGOUS TO THE RPG1 LOCUS OF SOYBEAN
A new disease resistance locus in Arabidopsis, RPS3, was identified using a previously cloned avirulence gene from a non-Arabidopsis pathogen. The avrB avirulence gene from the soybean pathogen Pseudomonas syringae pv. glycinea was transferred into a P. syringae pv. tomato strain that is virulent on Arabidopsis, and conversion to avirulence was assayed on Arabidopsis plants. The avrB gene had avirulence activity on most, but not all, Arabidopsis ecotypes. Of 53 ecotypes examined, 45 were resistant to a P. syringae pv. tomato strain carrying avrB, and eight were susceptible. The inheritance of this resistance was examined using crosses between the resistant ecotype Col-0 and the susceptible ecotype Bla-2. In F2 plants from this cross, the ratio of resistant: susceptible plants was approximately 3:1, indicating that resistance to P. syringae expressing avrB is determined by a single dominant locus in ecotype Col-0, which we have designated RPS3. Using RFLP analysis, RPS3 was mapped to chromosome 3, adjacent to markers M583 and G4523, and less-than-or-equal-to 1 cM from another disease resistance locus, RPM1. In soybean, resistance to P. syringae strains that carry avrB is controlled by the locus RPG1. Thus, RPG1 and RPS3 both confer avrB-specific disease resistance, suggesting that these genes may be homologs. DOI
