Characterization of the Role of CSLD proteins in Arabidopsis Cell Wall Deposition.

[摘要] Plant cells are surrounded by the plant cell wall, which defines the plant cell shape as well as provides structural integrity to plant tissues and organs. Among the various classes of polysaccharides found in the plant cell wall, the major load-bearing component is cellulose. Cellulose is synthesized by CESA proteins and disruption of these CESA genes results in either lethality or in growth defects in various developmental processes. However, defects in root hair tip-growth were primarily observed in csld2 or csld3 mutants rather than in cesa mutants. To better understand the role of CSLD proteins in Arabidopsis development, we examined the phenotypes of csld2, csld3, and csld5 mutants. We found that csld5 single mutants displayed dwarf stature, and the phenotypes were enhanced in csld2/csld5 and csld3/csld5 double mutants. Further examination showed the existence of incomplete cell walls in csld5 single and csld2/csld5 and csld3/csld5 double mutants. Using fluorescent fusions, we found that these three CSLD proteins localized on forming cell plates. A more precise temporal spatial analysis showed that CSLD5 was enriched on growing cell plates during cytokinesis. Shortly after cytokinesis was completed, CSLD5 was rapidly depleted from these newly-deposited cell walls. We further confirmed that CSLD5 was an unstable protein that might be degraded via APCCCS52A2 – 26S proteasome mediated pathways. We also investigated the functional redundancy of members of the CSLD family in root hair growth. We found that, when driven by the corresponding native promoters, only CSLD2 and CSLD3 proteins were detected in root hairs and both these proteins localized to apical membrane regions of growing root hairs. A promoter swap experiment showed that when expressed under control of the CSLD3 promoter, CSLD2 could fully restore root hair growth in csld3 mutant background. By contrast, CSLD5, when driven by the CSLD3 promoter, only partially rescued csld3 root hair phenotypes. Combined, the results presented in this thesis have revealed a unique cell-cycle mediated regulation of CSLD5, and described novel roles for all three vegetatively-expressed CSLD proteins in cell wall synthesis during cytokinesis. In addition, the functional redundancy between CSLD2, CSLD3, and CSLD5 during root hair growth was described.

[发布机构] University of Michigan

[效力级别] Cell Biology

[关键词] Plant Biology;Cell Biology;Cell Wall;Cell Cycle;Molecular;Cellular and Developmental Biology;Science;Molecular, Cellular and Developmental Biology