Title : Identification of two helicases as potential targets for mitigating drought stress in rice
Abstract:
Rice is consumed as a staple cereal crop by more than 3.2 billion people worldwide. But the constraint lies in the fact that rice cultivation requires about 35-43% of the world’s total irrigation. Due to global climatic changes, abiotic stress factors like drought and soil salinity are hampering its productivity and sustainability. Moreover, in addition to the already existing high demand, the escalating global population estimates that rice productivity must be increased by 26% in the next 25 years. Hence, with the help of improved genome engineering techniques, we have developed water use efficient (WUE) rice varieties which can withstand abiotic stress conditions like drought without compromising its yield. We have developed gain-of-function rice mutants via activation tagging. Analysis of these mutants under water deficit conditions, and further in silico studies led to the identification of two important helicases (SEN1 and XPB2) as potential targets for gene manipulation to develop stress tolerant varieties of rice. The drought tolerant attributes of SEN1 and XPB2 helicases has not been much explored. SEN1 and XPB2 are mostly associated with abnormal transcription termination and DNA repair respectively. A detailed study of the activationtagged lines has provided us with an insight on the probable role of these genes in drought stress tolerance. The expression analysis of the tagged mutants showed significant upregulation of the two genes in response to multiple simulated stress cues like salicylic acid, jasmonic acid, NaCl, polyethylene glycol (PEG), abscisic acid (ABA), and heat. We have also examined their expression patterns in response to infection with prominent rice pathogens such as Xanthomonas oryzae pv. oryzae and Rhizoctonia solani, which cause bacterial leaf blight and sheath blight respectively. Although not much significant upregulation was observed under biotic stress conditions, there was a noticeably high expression under ABA treatment. The lines showed better phenotypic and physiological characteristics in terms of increased fresh weight, root and shoot length, chlorophyll and proline content, photosynthetic performance, and yield when exposed to simulated stress factors. We have used ABA and PEG in order to mimic osmotic and drought stress conditions. Similar phenotypic traits were observed when the mutants were subjected to field-level drought stress. Further analyses of these plants are currently underway. We are also generating independent transgenic overexpression lines of these genes in rice for their further characterization. Taken together, our studies firmly establish that SEN1 and XPB2 can be considered important candidate genes for synthesizing tailor-made varieties of rice tolerant to drought stress.
