The Arabidopsis RING E3 Ubiquitin Ligase AtAIRP2 Plays Combinatory Roles with AtAIRP1 in Abscisic Acid-Mediated Drought Stress Responses

Seok Keun Cho,Moon Young Ryu,Woo Taek Kim,Bin Goo Kang,Dong Hye Seo

doi:10.1104/pp.111.185595

Seok Keun Cho, Moon Young Ryu + Show 3 more

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https://doi.org/10.1104/pp.111.185595

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Abstract

The ubiquitin (Ub)-26S proteasome pathway is implicated in various cellular processes in higher plants. AtAIRP1, a C3H2C3-type RING (for Really Interesting New Gene) E3 Ub ligase, is a positive regulator in the Arabidopsis (Arabidopsis thaliana) abscisic acid (ABA)-dependent drought response. Here, the AtAIRP2 (for Arabidopsis ABA-insensitive RING protein 2) gene was identified and characterized. AtAIRP2 encodes a cytosolic C3HC4-type RING E3 Ub ligase whose expression was markedly induced by ABA and dehydration stress. Thus, AtAIRP2 belongs to a different RING subclass than AtAIRP1 with a limited sequence identity. AtAIRP2-overexpressing transgenic (35S:AtAIRP2-sGFP) and atairp2 loss-of-function mutant plants exhibited hypersensitive and hyposensitive phenotypes, respectively, to ABA in terms of seed germination, root growth, and stomatal movement. 35S:AtAIRP2-sGFP plants were highly tolerant to severe drought stress, and atairp2 alleles were more susceptible to water stress than were wild-type plants. Higher levels of drought-induced hydrogen peroxide production were detected in 35S:AtAIRP2-sGFP as compared with atairp2 plants. ABA-inducible drought-related genes were up-regulated in 35S:AtAIRP2-sGFP and down-regulated in atairp2 progeny. The positive effects of AtAIRP2 on ABA-induced stress genes were dependent on SNF1-related protein kinases, key components of the ABA signaling pathway. Therefore, AtAIRP2 is involved in positive regulation of ABA-dependent drought stress responses. To address the functional relationship between AtAIRP1 and AtAIRP2, FLAG-AtAIRP1 and AtAIRP2-sGFP genes were ectopically expressed in atairp2-2 and atairp1 plants, respectively. Constitutive expression of FLAG-AtAIRP1 and AtAIRP2-sGFP in atairp2-2 and atairp1 plants, respectively, reciprocally rescued the loss-of-function ABA-insensitive phenotypes during germination. Additionally, atairp1/35S:AtAIRP2-sGFP and atairp2-2/35S:FLAG-AtAIRP1 complementation lines were more tolerant to dehydration stress relative to atairp1 and atairp2-2 single knockout plants. Overall, these results suggest that AtAIRP2 plays combinatory roles with AtAIRP1 in Arabidopsis ABA-mediated drought stress responses.

Highlights

The ubiquitin (Ub)-26S proteasome pathway is implicated in various cellular processes in higher plants
35S: AtAIRP2-sGFP transgenic plants were highly tolerant of severe drought stress; in contrast, atairp2 alleles were more susceptible to mild water stress than were wild-type plants. These results suggest that AtAIRP2, an Arabidopsis C3HC4-type RING E3 Ub ligase, is involved in positively regulating abscisic acid (ABA)-dependent drought stress responses
We identified atairp2 allele Arabidopsis mutants that were less sensitive to ABA treatment than were wild-type plants at the germination stage

Summary

Introduction

The ubiquitin (Ub)-26S proteasome pathway is implicated in various cellular processes in higher plants. AtAIRP1, a C3H2C3type RING (for Really Interesting New Gene) E3 Ub ligase, is a positive regulator in the Arabidopsis (Arabidopsis thaliana) abscisic acid (ABA)-dependent drought response. Atairp1/35S:AtAIRP2-sGFP and atairp2-2/ 35S:FLAG-AtAIRP1 complementation lines were more tolerant to dehydration stress relative to atairp and atairp single knockout plants Overall, these results suggest that AtAIRP2 plays combinatory roles with AtAIRP1 in Arabidopsis ABAmediated drought stress responses. Among the diverse gene sets induced by ABA are the E3 ubiquitin (Ub) ligases This suggests the existence of a functional network between ABAmediated stress responses and Ub-dependent protein degradation. Combinatory Roles of AtAIRP1 and AtAIRP2 RING E3s system is associated with many cellular processes as diverse as environmental stress responses, circadian rhythms, cell cycles, and hormone signaling (Moon et al, 2004; Smalle and Vierstra, 2004; Dreher and Callis, 2007; Vierstra, 2009; Lee and Kim, 2011). Polyubiquitinated substrate proteins are degraded by the 26S proteasome complex, while monoubiquitination or multiubiquitination confers nonproteolytic functions, such as DNA repair, protein trafficking, protein activity, and protein-protein interactions (Mukhopadhyay and Riezman, 2007; Jacobson et al, 2009)

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