Phosphoproteomics of Arabidopsis Highly ABA-Induced1 identifies AT-Hook Like10 phosphorylation required for stress growth regulation

Abstract

The Clade A protein phosphatase 2C Highly ABA-Induced 1 (HAI1) plays an important role in stress signaling yet little information is available on HAI1-regulated phosphoproteins.Quantitative phosphoproteomics identified phosphopeptides of increased abundance in hai1-2 in unstressed plants and in plants exposed to low water potential (drought) stress. The identity and localization of the phosphoproteins as well as enrichment of specific phosphorylation motifs indicated that these phosphorylation sites may be regulated directly by HAI1 or by HAI1regulated kinases including Mitogen-Activated Protein Kinases (MPKs), Sucrose-non fermenting Related Kinase 2 (SnRK2s) or Casein Kinases. One of the phosphosites putatively regulated by HAI1 was S313/S314 of AT Hook-Like10 (AHL10), a DNA binding protein of unclear function.HAI1 could directly dephosphorylate AHL10 in vitro and the level of HAI1 expression affected the abundance of phosphorylated AHL10 in vivo. AHL10 S314 phosphorylation was critical for restriction of plant growth under low water potential stress and for regulation of Jasmonic Acid and Auxin-related gene expression as well as expression of developmental regulators including Shootmeristemless (STM). These genes were also mis-regulated in hai1-2. AHL10 S314 phosphorylation was required for AHL10 complexes to form foci within the nucleoplasm, suggesting that S314 phosphorylation may control AHL10 association with the nuclear matrix or with other transcriptional regulators. These data identify a set of HAI1-affected phosphorylation sites, show that HAI1-regulated phosphorylation of AHL10 S314 controls AHL10 function and localization and also indicate that HAI1-AHL10 signaling coordinates growth with stress and defense responses.

The flip side of phospho‐signalling: Regulation of protein dephosphorylation and the protein phosphatase 2Cs

“…For example, the Clade A PP2Cs are known to regulate multiple members of the SnRK2 kinase family as part of their function in stress and ABA signalling (Umezawa et al, ). A recent phosphoproteomic analysis, using a loss of function mutant of highly ABA ‐ induced 1 ( hai1–2 , HAI1 is one of the Clade A PP2Cs), found an enrichment of MAPK, SnRK2/CPK, and casein kinase phosphorylation motifs (Wong et al, ). Also, phosphopeptides from casein kinases, CPK9, and other less‐characterized kinases were found among phosphopeptides of increased abundance in hai1–2 (Wong et al, ).…”

Global Quantitative Proteomics Studies Revealed Tissue-Preferential Expression and Phosphorylation of Regulatory Proteins in Arabidopsis

“…Previous studies in plants have uncovered many phosphoproteins and their phosphorylation sites [ 44 ]. The phospho-proteome of organs (e.g., roots or shoots), cells, or subcellular components (e.g., plasma membranes) was investigated under different growth and culture conditions [ 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 ]. The data are available in public databases such as PhosPhAt [ 59 ] or Plant Protein Phosphorylation Database (P3DB) [ 60 ].…”

AT-HOOK MOTIF NUCLEAR LOCALISED PROTEIN 18 as a Novel Modulator of Root System Architecture

“…They are predicted to form homo and hetero oligomers (trimers) via the plants and prokaryotes conserved (PPC) domain [15][26][16] [36]. The current knowledge indicates, that AHL genes are able to bridge regulation of several signal pathways acting as a nodes of the regulatory network integrating different inputs [37,38] The significance of overlapping expression domains, possible specific interactions among individual AHLs, and resulting selectivity of particular oligomers for DNA binding as well as interaction with other proteins via PPC domain, could further extend and specify the mode of AHL action. Their role as expression modulators might influence various levels of the process.…”