Alladi Ramakrishnan Hall

Advances in Chemical and Genetic approaches for enhancing abiotic stress tolerance in crops

Ashish Srivastava

BARC, Mumbai

Because plants are sessile, they have to tolerate many abiotic and biotic stress conditions. Chemical and genetic approaches are widely used to minimize stress induced damage in plants. The chemical approach relies on strengthening built-in plant defence using small molecules while genetic method alters gene expression using either mutation breeding or transgenic technology. Both chemical and genetic approaches are inter-dependent and complementary in nature. As a proof-of-concept, thiourea (a non-physiological thiol based ROS scavenger) application has been demonstrated to improve salt-tolerance in Indian mustard. Using thiourea as a chemical-probe, we established redox-microRNA-hormone based bifurcative model for mediating transcriptional reprogramming under salt stress conditions. Additionally, we have demonstrated the positive effect of thiourea treatment for enhancing growth and reducing grain arsenic stress accumulation in non-basmati and basmati varieties of indica rice under naturally arsenic contaminated sites of nadia district west-bengal. Seed priming with 500 PPM thiourea was optimized as "Essential" treatment for enhancing growth and two foliar applications at pre-flowering and grain filling stage as "Optional" treatment for early maturity and enhanced grain filling. Apart from redox and hormonal view, there are non-coding smallRNAs like miRNAs and siRNAs which regulate gene expression at post-transcription and transcriptional level, respectively. Studies were carried out to characterize the function of Stowaway1 transposon derived miR446b in rice. Initially, on the basis of smallRNA sequencing analysis, 21 nt mature sequence of miR446b was identified and its loading on AGO1c was confirmed. Using Short Tandem Target Mimic (STTM) technology, miR446b expression was knocked-down which resulted in reduced rate of seed germination and increased sensitivity against salt stress. On the basis of computational and RLM-RACE based studies, a PPR family gene was identified as target of miR446b. Genomic DNA containing PPR coding region was over-expressed and CDS sequence was analysed which indicated the existence of uORF along with main ORF. Both uORF and main ORF was independently mutated using CRISPR/Cas9 and the mutants showed significantly different phenotype. Thus, chemical and genetic approaches can be seen as inter-dependent and complementary approaches for enhancing abiotic stress in plants.