Abstract
Abscisic acid (ABA) plays versatile functions in regulating plant development and tolerance to various biotic and abiotic stresses. Towards elucidating the functions of one of the ABA receptors (ABARs) in rice, OsPYL10 was cloned from drought tolerant rice cv. Nagina 22 and was overexpressed under stress inducible RD29A promoter in a mega rice variety MTU1010 by using Agrobacterium mediated genetic transformation. Four single copy transgenic lines selected based on Southern blot analysis were used for physiological and molecular analysis. PYL10 receptor appears to regulate its ligand ABA accumulation as PYL10 overexpressing transgenics accumulated 2–3.3-fold higher levels of ABA than that of WT in flag leaf at anthesis under non-stress conditions. The enhanced accumulation of ABA was associated with enhanced expression of genes for ABA biosynthesis viz., ZEP1, NCED1, NCED2, NCED3, and NCED4 in transgenics than in WT plants. At seedling stage, PYL10 transgenics showed significantly higher survival rate under cold stress as compared with WT plants. qRT-PCR analysis showed that expression levels of cold responsive genes viz., DREB1F, MYB3R2, TPP1, COR410, DEHYDRIN, and LEA3 were significantly higher in PYL10 overexpressing transgenic lines as compared to WT plants under cold stress. PYL10 transgenic and WT plants grown in the same pot were subjected to -80 kPa drought stress and recovery treatments at vegetative and reproductive stages. At vegetative stage drought stress, three overexpressing lines showed significantly higher grain yield (40–58%) and at reproductive stage drought stress one of these overexpression lines showed two-fold higher grain yield than that of WT plants. Excised leaf water loss analysis showed that PYL10 transgenic lost about 20% less water than WT plants. At reproductive stage, OsPYL10 transgenic maintained higher RWC, membrane stability index, chlorophyll content, and accumulated lower amount of MDA and H2O2 as compared with WT plants. qRT-PCR analysis showed that expression levels of RAB16, Dehydrin, LEA3, and ABA45 were higher in PYL10 transgenics as compared with WT plants under drought stress. Thus, overall results showed that OsPYL10 overexpression has potential to improve both drought and cold stress tolerance of indica rice.
Highlights
Abscisic acid (ABA), a classical plant hormone, is involved in regulation of several physiological processes from germination to seed development and responses to various environmental stresses (Leung and Giraudat, 1998; Zhu, 2002; Shinozaki and Yamaguchi-Shinozaki, 2007; Finkelstein, 2013)
Rice array database revealed that OsPYL10 expression was downregulated under dehydration in all growth stages and highest induction was found in NaCl stress treatment in leaves (Supplementary Figure 1B)
Expression levels of multiple stress regulated effector genes such as OsCOR410, OsDEHYDRIN, and OsLEA3 were upregulated under cold stress, and the expression levels were significantly higher in PYL10 overexpression lines as compared with WT plants under cold stress (Figures 5G–I). These results suggest that expression of OsDREB1F, OsTPP1, OsCOR410, OsDehydrin, and OsLEA3 under cold stress is, at least in part, regulated through PYL ABA receptor signalling pathway
Summary
Abscisic acid (ABA), a classical plant hormone, is involved in regulation of several physiological processes from germination to seed development and responses to various environmental stresses (Leung and Giraudat, 1998; Zhu, 2002; Shinozaki and Yamaguchi-Shinozaki, 2007; Finkelstein, 2013). In the ligand-bound confirmation of PYL, the tryptophan residue (lock) of the clade A PP2C is inserted between the gate and latch loops and form PYL-ABA-PP2C complex which inhibits the activity of PP2Cs (Melcher et al, 2009; Miyazono et al, 2009; Santiago et al, 2009; Nishimura et al, 2009; Yin et al, 2009; Peterson et al, 2010). In the absence of ABA binding to PYL receptors, PP2Cs interact with and inhibit the activity of ABA-regulated SnRK2 family kinases viz., SnRK2.2, SnRK2.3, and SnRK2.6. In the presence of ABA, PYL receptor binds to ABA, interacts with PP2Cs and inhibits the activity of PP2Cs, and relieves the repression of SnRK2 activity by PP2Cs. SnRK2 kinases phosphorylate their target proteins to regulate stomatal closure and gene expression (Weiner et al, 2010; Zhu, 2016)
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