OsABI5 could prevent growth in a stressed environment. It plays a important role during plant development, especially in the regulation of plant fertility. It is associated with the ABA signaling pathway and stress tolerance. OsABI5 is possibly involved in the formation of microspores and the regulation of plant fertility. Two OsABI5 splicing variants were identified, designated OsABI5-1, and OsABI5-2 and their different expression patterns in tissues were analyzed. OsABI5 variants may have overlapping and distinct functions to fine tune gene expression in ABA signaling as transcription factors together with OsVP1 .
OsABI5-1 and OsABI5-2
- Sequence analysis showed that the two OsABI5 cDNAs are transcribed from the same initiation site and have a different exon. Exon skip was presented in the splicing variants. Amino acid analysis showed that the encoded peptides shared the identical bZIP domain, and the additional 10 amino acids of OsABI5-2 presented behind the leucine zipper at the C-terminal. Southern blot analysis indicated that the OsABI5 gene presented only one copy in the rice genome, which provide further support that OsABI5-1 and OsABI5-2 are different splicing variants of the OsABI5 gene.
- Differential transactivation activity in OsABI5-1 and OsABI5-2:
OsABI5-1 and OsABI5-2 had obvious transactivation capacity.By quantitative b-galactosidase assays using ONPG as a substrate, the OsABI5-1 fusion construct showed a nearly twofold higher activity level than the OsABI5-2 fusion construct, suggesting that deletion of additional protein sequences elevated the transactivation activity, and the additional 10 amino acids behind the bZIP domain of OsABI5-2 can affect the activity strength.
- DNA binding activity of OsABI5-1 and OsABI5-2 to the cis-acting G-box element in yeast:
- OsABI5-2 can function as a transacting factor for the G-box element and the additional 10 amino acids of OsABI5-2 are necessary for the binding specificity to the G-box. The binding activity of OsABI5-1 to the G-box element is disrupted by deleting the 10 amino acids.
- Interaction between OsABI5-1 and OsABI5-2:
OsABI5-1 and OsABI5-2 could interact directly in vitro, and that OsABI5-2 could interact with itself. In Arabidopsis, hetero and homo-dimerization among homologs of the ABI5 family have already been documented. Whether OsABI5-1 and OsABI5-2 could form heterodimers remains to be confirmed.
- RT-PCR: OsABI5 was induced within 1 h after ABA and high-salt treatment, and the mRNA level continuously increased up to 24 h. Cold treatment initially suppressed OsABI5 expression within 5 h, and then induced it to reach its maximum at 24 h. When plants were subjected to dehydration stress, OsABI5 expression was suppressed within 24 h(figure 1) .
- Semi-quantitative RT-PCR showed that the expression of OsABI5 was suppressed to different degrees and the decreased fertility rate of rice was correlated with the expression of OsABI5.
- Over-expression of OsABI5 in rice conferred high sensitivity to salt stress. Repression of OsABI5 promoted stress tolerance and resulted in low fertility of rice.
- RT-PCR showed that the OsABI5-2 transcript was constitutively detected in root, leaf, and young panicle. The expression abundance of OsABI5-1 was different in various tissues, with an expression in the leaf as high as OsABI5-2, and a low expression in the root and panicle (Figure 2). Expression of OsABI5-1 or OsABI5-2 can rescue ABA insensitivity of abi5-1 and confer ABA hypersensitivity to WT transgenic plants in Arabidopsis.
The OsABI5::GFP fusion protein was targeted to the nuclei of the cells, which suggested that OsABI5 was a nuclear protein and functioned as a transcription factor to regulate expression of down-stream genes.
- homology gene:
- It shares high amino acid sequence homology with Arabidopsis AtABI5and barley HvABI5 within five regions. Amino acids homology analysis showed that the OsABI5-encoded peptide contains a typical basic leucine zipper domain. The deduced amino acid sequence of OsABI5 contains conserved regions similar to other ABI5 or ABI5-like genes in other species. The Arabidopsis AtABI5 gene is involved in seed dormancy, maturation and stress responses. .
- OsABI5 displayed high homology with the Arabidopsis AtABI5 gene, suggesting similar functions in the adaptive stress response and the ABA signaling pathway. OsABI5 may have overlapping and distinct functions with AtABI5 during plant development.The ABI5 gene (ABA insensitive 5) of Arabidopsis encodes a basic leucine zipper factor required for ABA response in the seed and vegetative tissues. 
- Abscisic Acid (ABA) is an important phytohormone involved in abiotic stress resistance in plants. A group of bZIP transcription factors play important roles in the ABA signaling pathway in Arabidopsis. OsABI5(Os01g0859300) is a member of bZIP transcription factors,which also named OsbZIP10(Os01g0859300). Most of these OsbZIPs were significantly induced by ABA, ACC and abiotic stresses.
- All of the bZIPs could be classified into three subgroups. Each subgroup contains both rice and Arabidopsis bZIPs, indicating that the divergence of these subgroups predated the divergence of dicots and monocots. It also indicated that the protein sequences of these bZIPs were well conserved between dicots and monocots.
- Co-transformation experiments with ABI5 cDNA constructs resulted in specific transactivation of the ABA-inducible wheat Em, Arabidopsis AtEm6, bean-Phaseolin, and barley HVA1 and HVA22 promoters.
Labs working on this gene
Key Laboratory of Molecular and Developmental Biology, National Centre for Plant Gene Research, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, P.O. Box 2707, South 1-3, Zhongguancun, Beijing 100080, P.R. China
- Zou M, Guan Y, Ren H, et al. A bZIP transcription factor, OsABI5, is involved in rice fertility and stress tolerance[J]. Plant molecular biology, 2008, 66(6): 675-683.
- Zou M, Guan Y, Ren H, et al. Characterization of alternative splicing products of bZIP transcription factors OsABI5[J]. Biochemical and biophysical research communications, 2007, 360(2): 307-313.
- Brocard I M, Lynch T J, Finkelstein R R. Regulation and role of the Arabidopsis abscisic acid-insensitive 5 gene in abscisic acid, sugar, and stress response[J]. Plant Physiology, 2002, 129(4): 1533-1543.
- Gampala S S L, Finkelstein R R, Sun S S M, et al. ABI5 interacts with abscisic acid signaling effectors in rice protoplasts[J]. Journal of Biological Chemistry, 2002, 277(3): 1689-1694.
- Lu G, Gao C, Zheng X, et al. Identification of OsbZIP72 as a positive regulator of ABA response and drought tolerance in rice[J]. Planta, 2009, 229(3): 605-615.