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Protein post-translational modification by ubiquitination participates in many aspects of plant growth, development and stress responses.Covalent attachment of ubiquitin to targets is sequentially catalyzed by three enzymes (El, E2 and E3), among them E3 ligase functions importantly in substrate specificity.Several E3 ligases that involved in ABA signaling pathway have been identified, but the detail function mechanism of most E3 ligases are obscure.We have reported an RING type E3 ligase named SDIR1 in Arabidopsis which is a positive regulator of ABA signaling pathway.Given that SDIR1 is a membrane protein, a membrane-based yeast two-hybrid screen was performed in order to identify SDIR1 interaction proteins.We verified a protein named SDIRIP2 (SDIR1 interacting protein 2) can interact with SDIR1 by CoIP and firefly luciferase complementation imaging assays.In vitro pull down analysis showed SDIRIP2 can directly interact with SDIR1.sdirip2 mutant plants were sensitive to ABA and NaCl stress during germination and post germination, phenotype similar with SDIR1 over-expressed plants.In vitro assay showed ubiquitination and degradation of SDIRIP2 by 26S proteasome were mediated by SDIR1.Those data demonstrated SDIRIP2 was a substrate of SDIR1.Furthermore, the downstream ABA signaling molecule, the ABI5 protein level was higher under ABA and NaCl treatment in sdirip2 mutant and SDIR1 over-expressed plants compared with WT.In addition,we found that SDIRIP2 interacted with SOS3, and it enhanced the interaction between SOS2 and SOS3.The relationship between SDIR1 substrates will be further analyzed.