Regulation of ethylene biosynthesis and multiple ethylene signal transduction pathways in a model plant arabidopsis

Abstract

Ethylene is one of important plant hormones, and it plays important role in plant physiological regulation during plant life cycle. Arabidopsis can produce endogenous ethylene through ethylene biosynthesis pathway. ACC synthase (ACS) is one of the key enzymes in ethylene biosynthesis pathway in Arabidopsis plant. Proteases which can cleave ACS2 C-terminal were found in Arabidopsis in this study, and they were purified by FPLC method. Seven proteases were identified by LC-MS/MS, and three protease mutants were validated have lower protease activity than wild-type plant. One in vitro expressed protease still can process ACS2 C-terminus in proteolysis assay. Arabidopsis plant also has response to ethylene by five receptors, then ethylene signaling transduction through ethylene signaling pathway. It is believed that protein phosphorylation plays a key role in ethylene signaling, which is partially mediated by some uncharacterized pathway(s) independent to a known linear signaling pathway from ethylene receptors to transcription factors EIN3 and EIL1. To address how ethylene alters the cellular protein phosphorylation profile through these pathways, a differential and ¹⁵N s̠table i̠sotope l̠abeling i̠n A̲rabidopsis (SILIA or SIML)-based quantitative phosphoproteomic analysis was performed on 12 h ethylene-treated Arabidopsis ethylene-insensitive double loss-of-function mutant, ein3-1/eil11-1. Two and four phosphopeptides were identified up- and down-regulated by ethylene, respectively. Amongst the ethylene-regulated phosphoproteins, aquaporin protein PIP2;1 is of highly biological interest since the ethylene regulates the water permeability of plasma membrane through posttranslational regulation. Both LC-MS/MS and western-blot analysis showed PIP2;1 protein phosphorylation up-regulated by ethylene independent of EIN3/EIL1. Further study using transgenic plants confirms that ethylene regulates the water channels opening via a phosphorylation pathway independent to EIN3 and EIL1, which resulted in alteration of water flux rates cross plasma membrane. Taken together, our study suggests that the water channel activity is regulated by ethylene-mediated protein phosphorylation, which is largely independent to EIN3 and EIL1.

Date of Award	2015
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology