Halat Laryssa, Gyte Katherine, Wasteneys Geoffrey
Department of Botany, The University of British Columbia, Vancouver, British Columbia, V6T 1Z4, Canada.
Department of Botany, The University of British Columbia, Vancouver, British Columbia, V6T 1Z4, Canada
Plant Physiol. 2020 Dec;184(4):2154-2167. doi: 10.1104/pp.20.00474. Epub 2020 Oct 6.
The ability for plant growth to be optimized, either in the light or dark, depends on the intricate balance between cell division and differentiation in specialized regions called meristems. When Arabidopsis () seedlings are grown in the dark, hypocotyl elongation is promoted, whereas root growth is greatly reduced as a result of changes in hormone transport and a reduction in meristematic cell proliferation. Previous work showed that the microtubule-associated protein CLASP sustains root apical meristem size by influencing microtubule organization and by modulating the brassinosteroid signaling pathway. Here, we investigated whether CLASP is involved in light-dependent root growth promotion, since dark-grown seedlings have reduced root apical meristem activity, as observed in the null mutant. We showed that CLASP protein levels were greatly reduced in the root tips of dark-grown seedlings, which could be reversed by exposing plants to light. We confirmed that removing seedlings from the light led to a discernible shift in microtubule organization from bundled arrays, which are prominent in dividing cells, to transverse orientations typically observed in cells that have exited the meristem. Brassinosteroid receptors and auxin transporters, both of which are sustained by CLASP, were largely degraded in the dark. Interestingly, we found that despite the lack of protein, transcript levels were higher in dark-grown root tips. Together, these findings uncover a mechanism that sustains meristem homeostasis through CLASP, and they advance our understanding of how roots modulate their growth according to the amount of light and nutrients perceived by the plant.
植物生长在光照或黑暗条件下实现最优化的能力，取决于在称为分生组织的特定区域中细胞分裂与分化之间的复杂平衡。当拟南芥幼苗在黑暗中生长时，下胚轴伸长会得到促进，而由于激素运输的变化和分生细胞增殖的减少，根的生长会大幅降低。先前的研究表明，微管相关蛋白CLASP通过影响微管组织和调节油菜素类固醇信号通路来维持根尖分生组织的大小。在这里，我们研究了CLASP是否参与光依赖的根生长促进过程，因为正如在CLASP缺失突变体中观察到的那样，在黑暗中生长的幼苗根尖分生组织活性降低。我们发现，在黑暗中生长的幼苗根尖中，CLASP蛋白水平大幅降低，而将植物暴露于光照下可使其恢复。我们证实，将幼苗从光照条件下移出会导致微管组织发生明显变化，从在分裂细胞中突出的束状排列转变为通常在已离开分生组织的细胞中观察到的横向排列。油菜素类固醇受体和生长素转运蛋白都由CLASP维持，在黑暗中它们大多会降解。有趣的是，我们发现尽管缺乏蛋白，但在黑暗中生长的根尖中CLASP转录水平更高。总之，这些发现揭示了一种通过CLASP维持分生组织稳态的机制，并加深了我们对根如何根据植物感知到的光照和养分数量调节其生长的理解。
