Cell/Development/Systems

Abstract

C-5-4 - A difference of night and day: The microtubule-associated protein CLASP modulates plant root growth in the light and dark

Sunday, July 15
2:03 PM - 2:23 PM

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 thaliana 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 (RAM) size both by influencing microtubule (MT) organization and by modulating the brassinosteroid (BR) signalling pathway. Here, we investigated whether CLASP is involved in light-dependent root growth promotion, since dark-grown seedlings have dwarf RAMs that resemble the clasp-1 null mutant. We first confirmed that the BR-dependent reduction in CLASP’s expression and protein levels was mimicked in the root tips of dark-grown seedlings. We then showed that both increased BR signalling and the removal of seedlings from the light led to a discernible shift in microtubule (MT) organization from bundled arrays, which are prominent in dividing cells, to transverse orientations typically observed in cells that have exited the meristem. Interestingly, we found that CLASP’s promoter contains a G-box motif that is a common target for the hormone-activated transcription factors (TFs) PIF4 and BZR1 in many light-regulated genes. To determine if meristem development is controlled by this G-box motif, we mutated it such that CLASP expression was insensitive to the BR-activated TF BZR1. Plants with the mutated CLASP promoter had fewer cells in the meristem and altered responses to BR. Together, these findings uncover a remarkable feedback loop that sustains meristem homeostasis through CLASP, and advances our understanding of how roots modulate their growth according to the amount of light and hormone perceived by the plant. 


 

Co-Authors

Deirdre Khan – University of Manitoba; Mark Belmonte – University of Manitoba; Geoffrey Wasteneys – University of British Columbia

Laryssa Halat

University of British Columbia

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C-5-4 - A difference of night and day: The microtubule-associated protein CLASP modulates plant root growth in the light and dark



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