PECTATE LYASE LIKE12 patterns the guard cell wall to coordinate turgor pressure and wall mechanics for proper stomatal function in Arabidopsis

Abstract

Plant cell deformations are driven by cell pressurization and mechanical constraints imposed by the nanoscale architecture of the cell wall, but how these factors are controlled at the genetic and molecular levels to achieve different types of cell deformation is unclear. Here, we used stomatal guard cells to investigate the influences of wall mechanics and turgor pressure on cell deformation and demonstrate that the expression of the pectin-modifying gene PECTATE LYASE LIKE12 (PLL12) is required for normal stomatal dynamics in Arabidopsis thaliana. Using nanoindentation and finite element modeling to simultaneously measure wall modulus and turgor pressure, we found that both values undergo dynamic changes during induced stomatal opening and closure. PLL12 is required for guard cells to maintain normal wall modulus and turgor pressure during stomatal responses to light and to tune the levels of calcium cross-linked pectin in guard cell walls. Guard cell-specific knockdown of PLL12 caused defects in stomatal responses and reduced leaf growth, which were associated with lower cell proliferation but normal cell expansion. Together, these results force us to revise our view of how wall-modifying genes modulate wall mechanics and cell pressurization to accomplish the dynamic cellular deformations that underlie stomatal function and tissue growth in plants.

A Phloem-Expressed PECTATE LYASE-LIKE Gene Promotes Cambium and Xylem Development

“…Cross-sections of the stem showed that within the vascular strands, PLL12 was expressed primarily in the phloem. This localised expression pattern was in agreement with the reported role of PLL12 in stomatal guard cells ( Chen et al, 2021 ) and with reports of phloem-specific PLL12 expression in the root ( Brady et al, 2007 ; Kalmbach et al, 2022 ) and during in vitro differentiation ( Kondo et al, 2016 ).…”

“…Furthermore, PLL12 expression was located specifically in vascular cell types in a root transcriptomic atlas ( Brady et al, 2007 ) and was associated with vascular differentiation in vitro ( Kondo et al, 2016 ). Based on these data, we hypothesised that PLL12 might have a role in cell wall modification during vascular development, in addition to the previously described function in stomatal guard cells ( Chen et al, 2021 ).…”

“…To confirm the PLL12 expression during vascular development, we used the GUS reporter fused to the complete PLL12 gene. Previous reporter genes using GUS fused to 2 kb of the putative PLL12 promoter gave weak and variable expression ( Sun and Van Nocker, 2010 ) or suggested widespread expression ( Chen et al, 2021 ). Our ChIP-seq data, however, indicated RPL binding to intron 3 of PLL12 ( Supplementary Figure 1 ), raising the possibility that regulatory sequences have been missed in previous constructs.…”

“…We next analysed the function of PLL12 , focussing especially on vascular development. For this, we used two independent T-DNA mutant alleles, pll12-1 (SAIL 1207_A07) ( Chen et al, 2021 ) and pll12-2 (SAIL 1149_C06). As reported, pll12-1 had undetectable PLL12 mRNA ( Chen et al, 2021 ), and the same was seen for pll12-2 ( Supplementary Figure 2 ).…”

Polygalacturonase activity promotes aberrant cell separation in the quasimodo2 mutant of Arabidopsis thaliana

“…Protein was extracted from 0.5 to 1 g of pooled 6-day-old etiolated seedlings for each genotype and assays were performed exactly as described in Xiao et al (2014) for PG activity and Chen et al (2021) for PL activity, with the exception that for the PL activity assay, absorbance was measured at 250 nm instead of 237 nm.…”