Plant cells are immobile; thus, plant growth and development depend on cell expansion rather than cell migration. The molecular mechanism by which the plasma membrane initiates changes in the cell expansion rate remains elusive. We found that a secreted peptide, RALF (rapid alkalinization factor), suppresses cell elongation of the primary root by activating the cell surface receptor FERONIA in Arabidopsis thaliana. A direct peptide-receptor interaction is supported by specific binding of RALF to FERONIA and reduced binding and insensitivity to RALF-induced growth inhibition in feronia mutants. Phosphoproteome measurements demonstrate that the RALF-FERONIA interaction causes phosphorylation of plasma membrane H+–adenosine triphosphatase 2 at Ser899, mediating the inhibition of proton transport. The results reveal a molecular mechanism for RALF-induced extracellular alkalinization and a signaling pathway that regulates cell expansion.

/pdf/a-peptide-hormone-and-its-receptor-protein-kinase-regulate-3330ive7as.pdf

A Peptide Hormone and Its Receptor Protein Kinase Regulate Plant Cell Expansion

The plant hormone auxin promotes cell expansion. Forty years ago, the acid growth theory was proposed, whereby auxin promotes proton efflux to acidify the apoplast and facilitate the uptake of solutes and water to drive plant cell expansion. However, the underlying molecular and genetic bases of this process remain unclear. We have previously shown that the SAUR19-24 subfamily of auxin-induced SMALL AUXIN UP-RNA (SAUR) genes promotes cell expansion. Here, we demonstrate that SAUR proteins provide a mechanistic link between auxin and plasma membrane H+-ATPases (PM H+-ATPases) in Arabidopsis thaliana. Plants overexpressing stabilized SAUR19 fusion proteins exhibit increased PM H+-ATPase activity, and the increased growth phenotypes conferred by SAUR19 overexpression are dependent upon normal PM H+-ATPase function. We find that SAUR19 stimulates PM H+-ATPase activity by promoting phosphorylation of the C-terminal autoinhibitory domain. Additionally, we identify a regulatory mechanism by which SAUR19 modulates PM H+-ATPase phosphorylation status. SAUR19 as well as additional SAUR proteins interact with the PP2C-D subfamily of type 2C protein phosphatases. We demonstrate that these phosphatases are inhibited upon SAUR binding, act antagonistically to SAURs in vivo, can physically interact with PM H+-ATPases, and negatively regulate PM H+-ATPase activity. Our findings provide a molecular framework for elucidating auxin-mediated control of plant cell expansion.

/pdf/saur-inhibition-of-pp2c-d-phosphatases-activates-plasma-1dmsthvbc6.pdf

SAUR Inhibition of PP2C-D Phosphatases Activates Plasma Membrane H+-ATPases to Promote Cell Expansion in Arabidopsis

https://www.cell.com/molecular-plant/pdf/S1674-2052(15)00427-X.pdf

Plasma Membrane H+-ATPase Regulation in the Center of Plant Physiology

https://www.cell.com/molecular-plant/pdf/S1674-2052(15)00236-1.pdf

SAUR Proteins as Effectors of Hormonal and Environmental Signals in Plant Growth.

-ATPases 并且支持房间扩大。除了植物生长素，几另外的荷尔蒙和环境因素也调整 SAUR 基因表示。我们建议 SAUR 是调整植物生长和开发的神经质、环境的信号的关键受动器产量。

Rachel B. Nelson

Papers

Molecular Characterization of Mutant Arabidopsis Plants with Reduced Plasma Membrane Proton Pump Activity