Protein phosphatase 2A promotes stomatal development by stabilizing SPEECHLESS in Arabidopsis

Abstract

Stomatal guard cells control gas exchange that allows plant photosynthesis but limits water loss from plants to the environment. InArabidopsis, stomatal development is mainly controlled by a signaling pathway comprising peptide ligands, membrane receptors, a mitogen-activated protein kinase (MAPK) cascade, and a set of transcription factors. The initiation of the stomatal lineage requires the activity of the bHLH transcription factor SPEECHLESS (SPCH) with its partners. Multiple kinases were found to regulate SPCH protein stability and function through phosphorylation, yet no antagonistic protein phosphatase activities have been identified. Here, we identify the conserved PP2A phosphatases as positive regulators ofArabidopsisstomatal development. We show that mutations in genes encoding PP2A subunits result in lowered stomatal production inArabidopsis. Genetic analyses place the PP2A function upstream of SPCH. Pharmacological treatments support a role for PP2A in promoting SPCH protein stability. We further find that SPCH directly binds to the PP2A-A subunits in vitro. In plants, nonphosphorylatable SPCH proteins are less affected by PP2A activity levels. Thus, our research suggests that PP2A may function to regulate the phosphorylation status of the master transcription factor SPCH in stomatal development.

Roles of plant retinoblastoma protein: cell cycle and beyond

“…In addition, formative divisions and cell fate acquisition in the stomatal lineage that give rise to mature stomata require the concerted action of various transcription factors and RBR1 (reviewed in Han & Torii, ). Protodermal cells in the epidermis of leaf primordia, the meristemoid mother cells (MMC), accumulate SPEECHLESS (SPCH), a substrate of various MAP kinases and of the protein phosphatase PP2A that together regulate SPCH stability (Bian et al , ). SPCH triggers asymmetrical cell division in MMCs, giving rise to a pavement cell and an immature meristemoid (M).…”

Phenotyping stomatal closure by thermal imaging for GWAS and TWAS of water use efficiency-related genes

“…Thirty five orthologs of genes implicated in stomatal or epidermal cell patterning belong to enriched GO terms including plant epidermis morphogenesis , cell cycle DNA replication , plant-type cell wall biogenesis , and plastid organization (Supplementary Table S7). Arabidopsis genes known to impact stomatal development or patterning which had sorghum orthologs found in the highest confidence candidates for g s thermal traits included: the Mitogen-activated protein kinase kinase kinase YODA (Bergmann et al, 2004), the FAMA bHLH-type transcription factor (Ohashi-Ito and Bergmann 2006), the cyclin-dependent kinase CDKB1;1 (Boudolf et al, 2004), the phytochrome interacting factor 1 (PIF1, Klermund et al, 2016), somatic embryogenic receptor kinase 1 (SERK1, Meng et al 2015), DNA-directed RNA polymerase II subunit 2 (Chen et al, 2016), the chromatin regulator Enhanced Downy Mildew 2 (EDM2, Wang et al, 2016), Protein Phosphatase 2A (Bian et al, 2020), GATA, NITRATE-INDUCIBLE, CARBON METABOLISM-INVOLVED (GNC, Klermund et al, 2016), the extra-large GTP-binding protein (XLG3, Chakravorty et al, 2015), and the ARF guanine-nucleotide exchange factor GNOM (Le et al, 2014). Focusing on grasses, SOBIC.010G277300 shares 96 % predicted protein sequence homology with GRMZM2G057000 in maize.…”

SPEECHLESS and MUTE Mediate Feedback Regulation of Signal Transduction during Stomatal Development

“…at a specific site. However, overexpression of PP2A-A did not exhibit a visible phenotype, which indicates that the other two subunits are also required for SPCH stabilization and subsequent consequences, as shown in Figure 6 [81]. Figure 6.…”

“…PP2A function is required for the prophase band formation in Arabidopsis and the orientation of cell division in maize during stomatal development [79,80]. Recently, the role of PP2A-mediated positive regulation SPCH stability by direct interaction between SPCH and A subunit of PP2A to promote stomatal development has been reported [81].…”