Kim JH, Kim WT

RING E3 ubiquitin (Ub) ligases have been implicated in cellular response to the stress hormone abscisic acid (ABA) as well as to environmental stresses in higher plants. Here, an atairp3 (Arabidopsis thaliana ABA insensitive RING protein 3) loss-of-function mutant line was isolated due to its hyposensitivity to ABA during its ...

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germination stage as compared to wild-type plants. AtAIRP3 contains a single C3HC4-type RING motif, a putative myristoylation site, and a DAR2 domain. Unexpectedly, AtAIRP3 was identified as LOG2 (Loss of GDU2), which was recently shown to participate in an amino acid export system via interaction with GDU1 (GLUTAMINE DUMPER1). Thus, AtAIRP3 was renamed as AtAIRP3/LOG2. Transcript levels of AtAIRP3/LOG2 were upregulated by drought, high salinity, and ABA, suggesting a role for this factor in abiotic stress responses. The atairp3/log2-2 knock-out mutant and 35S:AtAIRP3-RNAi knock-down transgenic plants displayed impaired ABA-mediated seed germination and stomata closure. Co-suppression and complementation studies further supported a positive role for AtAIRP3/LOG2 in ABA responses. Suppression of AtAIRP3/LOG2 resulted in marked hypersensitive phenotypes toward high salinity and water deficit relative to wild-type plants. These results suggest that Arabidopsis RING E3 AtAIRP3/LOG2 is a positive regulator of the ABA-mediated drought and salt stress tolerance mechanism. Using yeast two-hybrid, in vitro and in vivo immunoprecipitation, cell-free protein degradation, and in vitro ubiquitination assays, RD21 (Responsive to Dehydration 21) was identified as a substrate protein of AtAIRP3/LOG2. Collectively, our data suggest that AtAIRP3/LOG2 plays dual functions in ABA-mediated drought stress responses and in an amino acid export pathway in Arabidopsis.

Date: May. 21, 2013

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