Abstract
In many plant species, roots maintain specific growth angles relative to the direction of gravity, known as gravitropic set point angles (GSAs). These contribute to the efficient acquisition of water and nutrients. AtLAZY1/LAZY1-LIKE (LZY) genes are involved in GSA control by regulating auxin flow toward the direction of gravity in Arabidopsis. Here, we demonstrate that RCC1-like domain (RLD) proteins, identified as LZY interactors, are essential regulators of polar auxin transport. We show that interaction of the CCL domain of LZY with the BRX domain of RLD is important for the recruitment of RLD from the cytoplasm to the plasma membrane by LZY. A structural analysis reveals the mode of the interaction as an intermolecular β-sheet in addition to the structure of the BRX domain. Our results offer a molecular framework in which gravity signal first emerges as polarized LZY3 localization in gravity-sensing cells, followed by polar RLD1 localization and PIN3 relocalization to modulate auxin flow.
Highlights
In many plant species, roots maintain specific growth angles relative to the direction of gravity, known as gravitropic set point angles (GSAs)
The RCC1-like domain (RLD) family proteins are conserved among land plants and share a similar domain combination containing a pleckstrin homology (PH) domain, regulator of chromosome condensation 1 (RCC1)-like motif repeats, a Fab1/YGL023/Vps27/EEA1 (FYVE) domain, and a Brevis radix (BRX) domain[26] (Fig. 1a)
The results demonstrated that at least RLD1 and RLD4 are involved in GSA control of lateral roots (LRs)
Summary
Roots maintain specific growth angles relative to the direction of gravity, known as gravitropic set point angles (GSAs) These contribute to the efficient acquisition of water and nutrients. Plant organs sense gravity as a directional cue to control their growth orientation and shoots typically grow upward while roots grow downward This growth response to gravity is known as gravitropism[1,2,3]. We previously demonstrated that LZY genes facilitate polar auxin transport toward the direction of gravity, possibly through the control of asymmetric PIN3 expression in the root cap columella of LRs13. We identify RCC1-like domain (RLD) proteins as LZY interactors and reveal that RLD is a regulator of polar auxin transport that controls the abundance and localization of the PIN protein in various developmental processes including GSA control.
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