Arabidopsis pavement cell shape formation involves spatially confined ROPGAP regulators

Abstract

How cells acquire complex shapes is a fundamental question in biology. Lauster et al. show that PHGAP/RENs associate with cortical microtubules preferentially along anticlinal cell faces, and they facilitate the spatially distinct deactivation of ROP2 in indentations. This interplay is essential for multipolarity of epidermal pavement cells.

ROPGAP-dependent interaction between brassinosteroid and ROP2-GTPase signaling controls pavement cell shape in Arabidopsis

“…Indeed, PHGAP deletion mutants lacking the non-catalytic domains were unable to complement the phgap1phgap2 mutant and did not properly localize in pavement cells. 51 Similarly, the C-terminal part of the close PHGAP homolog, REN1, containing coiled-coil domains and active in continuous tip growth, was not essential for the GAP activity, but was needed for the apical REN1 localization in the pollen tubes. 36 Post-translational regulation of GAPs had previously not been reported in plants, whereas in mammalian cells a number of GAPs are known to be regulated by phosphorylation that can affect either their GAP activity or their subcellular localization.…”

“…However, BIN2 might not affect the anticlinal cell wall localization of PHGAP2 by direct phosphorylation. It has been shown that the indentation enrichment of PHGAPs depends on MTs, 51 of which the protein stability is regulated by BIN2 phosphorylation. 38 It remains to be determined whether BIN2 regulates the indentation enrichment of PHGAP2 through phosphorylation and stabilization of MTs.…”

“…Additionally, PHGAP1 and PHGAP2 interacted with ROP2, but not with ROP6, in both yeast and Arabidopsis cells and bacterially expressed RIC1 could bind more activated ROP2, but not ROP6, in the phgap1phgap2 mutant. 51 The reason for the PHGAP enrichment in the pavement cell indentations, in which ROP6 locally activates RIC1 to restrict cell outgrowth, might be that PHGAPs are required to limit the ROP2 activity in the indentation region. 51 Indeed, this hypothesis is plausible because the GFP-ROP2 was ubiquitously distributed in the plasma membrane of the abaxial epidermis (Figure S2C), albeit more abundantly in the stomatal lineage cells.…”

“…51 The reason for the PHGAP enrichment in the pavement cell indentations, in which ROP6 locally activates RIC1 to restrict cell outgrowth, might be that PHGAPs are required to limit the ROP2 activity in the indentation region. 51 Indeed, this hypothesis is plausible because the GFP-ROP2 was ubiquitously distributed in the plasma membrane of the abaxial epidermis (Figure S2C), albeit more abundantly in the stomatal lineage cells.…”

“…65 Interestingly, PHGAPs associate with MTs through their C-terminal domain either directly or indirectly (via additional interactors) in the indentations. 51 One possible scenario could involve the MT-targeted IQ67 DOMAIN proteins, some of which interact with either PHGAPs or GSK3. 40,66 Although it is still unclear how MTs, PHGAPs and BIN2 interact, the MT stabilization in the indentations will also require that BIN2 remains active.…”