Protein Phosphatase 2A Controls Ethylene Biosynthesis by Differentially Regulating the Turnover of ACC Synthase Isoforms

Abstract

The gaseous hormone ethylene is one of the master regulators of development and physiology throughout the plant life cycle. Ethylene biosynthesis is stringently regulated to permit maintenance of low levels during most phases of vegetative growth but to allow for rapid peaks of high production at developmental transitions and under stress conditions. In most tissues ethylene is a negative regulator of cell expansion, thus low basal levels of ethylene biosynthesis in dark-grown seedlings are critical for optimal cell expansion during early seedling development. The committed steps in ethylene biosynthesis are performed by the enzymes 1-aminocyclopropane 1-carboxylate synthase (ACS) and 1-aminocyclopropane 1-carboxylate oxidase (ACO). The abundance of different ACS enzymes is tightly regulated both by transcriptional control and by post-translational modifications and proteasome-mediated degradation. Here we show that specific ACS isozymes are targets for regulation by protein phosphatase 2A (PP2A) during Arabidopsis thaliana seedling growth and that reduced PP2A function causes increased ACS activity in the roots curl in 1-N-naphthylphthalamic acid 1 (rcn1) mutant. Genetic analysis reveals that ethylene overproduction in PP2A-deficient plants requires ACS2 and ACS6, genes that encode ACS proteins known to be stabilized by phosphorylation, and proteolytic turnover of the ACS6 protein is retarded when PP2A activity is reduced. We find that PP2A and ACS6 proteins associate in seedlings and that RCN1-containing PP2A complexes specifically dephosphorylate a C-terminal ACS6 phosphopeptide. These results suggest that PP2A-dependent destabilization requires RCN1-dependent dephosphorylation of the ACS6 C-terminus. Surprisingly, rcn1 plants exhibit decreased accumulation of the ACS5 protein, suggesting that a regulatory phosphorylation event leads to ACS5 destabilization. Our data provide new insight into the circuitry that ensures dynamic control of ethylene synthesis during plant development, showing that PP2A mediates a finely tuned regulation of overall ethylene production by differentially affecting the stability of specific classes of ACS enzymes.

Functional Phosphoproteomic Analysis Reveals That a Serine-62-Phosphorylated Isoform of Ethylene Response Factor110 Is Involved in Arabidopsis Bolting

“…The dephosphorylation of the Ser-62 phosphosite, elicited by a higher dose of ethylene, might result from ethylene-enhanced phosphatase activity. As protein phosphatase 2A is known to destabilize ACS6 via dephosphorylation of the ACC synthase C terminus (Skottke et al, 2011), this complex may be involved in the dephosphorylation of ERF110.…”

Producing the Ethylene Signal: Regulation and Diversification of Ethylene Biosynthetic Enzymes

“…MAPK activity on ACS6 is counteracted by protein phosphatase2A (PP2A)-mediated dephosphorylation (Skottke et al, 2011); moreover, okadaic acid and calyculin (which inhibit both PP2A and PP1) have been shown to cause the accumulation of stabilized MAPK-and CDPKphosphorylated SlACS2 in tomato fruit (Kamiyoshihara et al, 2010). Unphosphorylated type 1 isozymes are rapidly turned over via a 26S proteasome-dependent pathway, and the noncatalytic C-terminal region containing the CDPK and MAPK phosphorylation motifs is sufficient to confer instability on reporter protein fusions (Joo et al, 2008).…”

Diverse responses of wild and cultivated tomato to BABA, oligandrin andOidium neolycopersiciinfection

“…Based on this result, the transcript levels of key enzymes involved in the ET synthesis pathway, namely ACC synthase and ACC oxidase, were determined along with quantification of the production of ET. On the basis of previous studies of different ACC synthase isoforms in Arabidopsis (Skottke et al, 2011;Li et al, 2012) and ACC synthase and oxidase in tomato (Lincoln et al, 1993;Kim et al, 1998;Cohn and Martin, 2005;Shi and Zhang, 2014;Yim et al, 2014), three candidate transcripts for each enzyme (ACS1a, ACS2, ACS6 for ACC synthase, and ACO1, ACO 1-like and ACO 4-like for ACC oxidase) with suspected roles in pathogenesis processes were selected.…”