OsSDIR1 is a functional E3 ubiquitin ligase which plays crucial roles in the plant response to abiotic stress like drought and NaCl.
OsSDIR1 was detected in all tissues of rice and up-regulated by drought and NaCl, but not by ABA. In vitro ubiquitination assays demonstrated that OsSDIR1 is a functional E3 ubiquitin ligase and that the RING finger region is required for its activity. OsSDIR1 could complement the drought sensitive phenotype of the sdir1 mutant and overexpressing transgenic Arabidopsis were more sensitive to ABA, indicating that the OsSDIR1 gene is a functional ortholog of SDIR1. Upon drought treatment, the OsSDIR1-transgenic rice showed strong drought tolerance compared to control plants. Analysis of the stomata aperture revealed that there were more closed stomatal pores in transgenic plants than those of control plants. This result was also confirmed by the water loss assay and leaf related water content (RWC) measurements during drought treatment.
The expression of OsSDIR1 was detected in all tissues of rice, including leaves, stems, roots and spikes, and the highest level was found in the roots. the transcript level of OsSDIR1 was up-regulated by drought and NaCl. Upon drought treatment, the expression level of OsSDIR1 gene was slightly increased during the early period of the treatment time course, and an obvious induction was detected at 24 h. The induction by NaCl appeared very early, at 1 h after the start of the treatment and about a threefold level of induction was detected, reaching the highest at 4 h after which the expression returned back to normal levels. It is interesting that the expression of OsSDIR1 was suppressed by cold treatment, and the reduction of expression was observed from the 2-h time point, with almost no expression detectable from 8 h onward. No changes in expression levels were detected by the treatment with a stress-related hormone ABA at any point in the time course
Transient expression in onion epidermal cells demonstrated that GFP alone was found in both the cytosol and the nucleus, whereas GFP-OsSDIR1 was found densely localized in the plasma membrane and other intracellular membranes. The fluorescence was also detected on the membrane of the nucleus since the pattern appeared to be on the surface, and it is also different from the dense localization of GFP itself in the nucleus. Given the high similarity of amino acids between Arabidopsis SDIR1 and OsSDIR1, the OsSDIR1 protein could be localized on the intracellular membrane
It was found that the SDIR1 protein is plant specific, and homologs could only be detected in plant species rather than in other organisms. SDIR1 homologs were found both in mono- and dicotyledonous plants. Only one rice homolog composed of 280 amino acids with 69% identity and 76% similarity to Arabidopsis SDIR1 was identified. It is interesting that four homologs were detected in the EST database from grape (Vitis vinifera), with identities of 72, 70, 68 and 57%. SDIR1 homologs all contain two putative transmembrane domains at the N-terminus and a C3H2C3 RING finger at the C-terminus of the protein.
Labs working on this gene
XieQi. State Key Laboratory of Plant Genomics, National Center for Plant Gene Research, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Datun Road, Beijing 100101, China e-mail: email@example.com
1.Gao T1, Wu Y, Zhang Y. et al. OsSDIR1 overexpression greatly improves drought tolerance in transgenic rice.Plant Mol Biol. 2011 May;76(1-2):145-56. doi: 10.1007/s11103-011-9775-z