Abstract
BackgroundFamily members of sucrose non-fermenting 1-related kinase 2 (SnRK2), being plant-specific serine/threonine protein kinases, constitute the central core of abscisic acid (ABA)-dependent and ABA-independent signaling pathways, and are key regulators of abiotic stress adaptation in plants. We report here the functional characterization of SAPK9 gene, one of the 10 SnRK2s of rice, through developing gain-of-function and loss-of-function phenotypes by transgenesis.ResultsThe gene expression profiling revealed that the abundance of single gene-derived SAPK9 transcript was significantly higher in drought-tolerant rice genotypes than the drought-sensitive ones, and its expression was comparatively greater in reproductive stage than the vegetative stage. The highest expression of SAPK9 gene in drought-tolerant Oryza rufipogon prompted us to clone and characterise the CDS of this allele in details. The SAPK9 transcript expression was found to be highest in leaf and upregulated during drought stress and ABA treatment. In silico homology modelling of SAPK9 with Arabidopsis OST1 protein showed the bilobal kinase fold structure of SAPK9, which upon bacterial expression was able to phosphorylate itself, histone III and OsbZIP23 as substrates in vitro. Transgenic overexpression (OE) of SAPK9 CDS from O. rufipogon in a drought-sensitive indica rice genotype exhibited significantly improved drought tolerance in comparison to transgenic silencing (RNAi) lines and non-transgenic (NT) plants. In contrast to RNAi and NT plants, the enhanced drought tolerance of OE lines was concurrently supported by the upgraded physiological indices with respect to water retention capacity, soluble sugar and proline content, stomatal closure, membrane stability, and cellular detoxification. Upregulated transcript expressions of six ABA-dependent stress-responsive genes and increased sensitivity to exogenous ABA of OE lines indicate that the SAPK9 is a positive regulator of ABA-mediated stress signaling pathways in rice. The yield-related traits of OE lines were augmented significantly, which resulted from the highest percentage of fertile pollens in OE lines when compared with RNAi and NT plants.ConclusionThe present study establishes the functional role of SAPK9 as transactivating kinase and potential transcriptional activator in drought stress adaptation of rice plant. The SAPK9 gene has potential usefulness in transgenic breeding for improving drought tolerance and grain yield in crop plants.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0845-x) contains supplementary material, which is available to authorized users.
Highlights
Members of sucrose non-fermenting 1-related kinase 2 (SnRK2), being plant-specific serine/ threonine protein kinases, constitute the central core of abscisic acid (ABA)-dependent and ABA-independent signaling pathways, and are key regulators of abiotic stress adaptation in plants
The real-time PCR analysis of before stress (BS), after stress (AS) and after recovery (AR) samples revealed that the expression level of SAPK9 transcript in O. rufipogon is substantially greater than the other drought-tolerant genotypes viz., O. nivara, Nagina22, Manipuri and Vandana in both vegetative stage (Fig. 1a) and reproductive stage (Fig. 1b)
The SAPK9 transcript expression has been found to be differentially regulated in the selected drought-tolerant and droughtsensitive rice genotypes, and its expression is comparatively more elevated in reproductive stage than the vegetative stage
Summary
Members of sucrose non-fermenting 1-related kinase 2 (SnRK2), being plant-specific serine/ threonine protein kinases, constitute the central core of abscisic acid (ABA)-dependent and ABA-independent signaling pathways, and are key regulators of abiotic stress adaptation in plants. Plants, being sessile are incessantly confronted by different environmental stresses, which include drought, high salinity, and extreme temperature, affecting both biomass productivity and grain yield of crops. To cope with such adverse multiple stresses, diverse molecular and physiological mechanisms have been evolved by the plant kingdom in general and a plant species in particular. The members of SnRK2 family work at the merging point of the ABA-dependent and ABA-independent stress signaling pathways
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