4. 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.
2.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
1. 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
