A type III ACC synthase, ACS7, is involved in root gravitropism in Arabidopsis thaliana

Abstract

Ethylene is an important plant hormone that regulates developmental processes in plants. The ethylene biosynthesis pathway is a highly regulated process at both the transcriptional and post-translational level. The transcriptional regulation of these ethylene biosynthesis genes is well known. However, post-translational modifications of the key ethylene biosynthesis enzyme 1-aminocyclopropane-1-carboxylate (ACC) synthase (ACS) are little understood. In vitro kinase assays were conducted on the type III ACS, AtACS7, fusion protein and peptides to determine whether the AtACS7 protein can be phosphorylated by calcium-dependent protein kinase (CDPK). AtACS7 was phosphorylated at Ser216, Thr296, and Ser299 by AtCDPK16 in vitro. To investigate further the function of the ACS7 gene in Arabidopsis, an acs7-1 loss-of-function mutant was isolated. The acs7-1 mutant exhibited less sensitivity to the inhibition of root gravitropism by treatment with the calcium chelator ethylene glycol tetraacetic acid (EGTA). Seedlings were treated with gradient concentrations of ACC. The results showed that a certain concentration of ethylene enhanced the gravity response. Moreover, the acs7-1 mutant was less sensitive to inhibition of the gravity response by treatment with the auxin polar transport inhibitor 1-naphthylphthalamic acid, but exogenous ACC application recovered root gravitropism. Altogether, the results indicate that AtACS7 is involved in root gravitropism in a calcium-dependent manner in Arabidopsis.

Multilayered Regulation of Ethylene Induction Plays a Positive Role in Arabidopsis Resistance against Pseudomonas syringae

“…Pathway(s) that regulate ACS7 expression are unclear at present. Despite lacking a potential phosphorylation site in the C terminus, ACS7 was recently shown to be phosphorylated by a calcium-dependent protein kinase (CPK) activity at the N terminus, and phosphorylation could also lead to protein stabilization and ethylene production (Huang et al, 2013).…”

TheArabidopsis14-3-3 Protein RARE COLD INDUCIBLE 1A Links Low-Temperature Response and Ethylene Biosynthesis to Regulate Freezing Tolerance and Cold Acclimation

“…Some 14-3-3 proteins have been reported to regulate ET biosynthesis, and consequently ET levels, by interacting with ACS isoforms and controlling their stability (Chang et al, 2009;Huang et al, 2013;Yoon and Kieber, 2013). We decided to examine the possibility that RCI1A could also control ET content by interacting with ACS proteins.…”

“…Active roles of 14-3-3 proteins in plant hormone signaling have been reported for gibberellic acid, ABA, and brassinosteroids (Gampala et al, 2007;Schoonheim et al, 2007;Nakata et al, 2009). Recently, 14-3-3 proteins were found to interact in vivo with a subset of proteins linked to ET biosynthesis, including several ACC SYNTHASE (ACS) isoforms, regulating their activity (Chang et al, 2009;Huang et al, 2013;Yoon and Kieber, 2013), which strongly suggests that they also play a role in the ET response. Regarding the implication of 14-3-3 proteins in mediating stress signaling, a number of studies have demonstrated that they have an important function in plant responses to biotic stresses (Gökirmak et al, 2010).…”

Molecular mechanisms of gravity perception and signal transduction in plants

“…Calcium may therefore be assumed to be upstream of auxin in gravity signalling, but pharmacological studies suggest that the first peak of the calcium response in stems and the plateau of the second response are both auxin-transport dependent (Toyota et al 2008a). Calcium chelator-induced loss of root gravitropism was compromised in ACS7 (key ethylene biosynthesis enzyme) mutant, suggesting that ACS7 is involved in gravitropism downstream to calcium (Huang et al 2013). Inhibitors of mechanosensitive ion channels reduce the sedimentation of starch-rich chloroplasts in gravisensitive stem cells (Friedman et al 1998).…”