Physiological and molecular signatures reveal differential response of rice genotypes to drought and drought combination with heat and salinity stress

Rice is the staple food for more than 3.5 billion people worldwide. The sensitivity of rice to heat, drought, and salinity is well documented. However, rice response to combinations of these stresses is not well understood. A contrasting set of rice genotypes for heat (N22, Gharib), drought (Moroberekan, Pusa 1121) and salinity (Pokkali, IR64) were selected to characterize their response under drought, and combination of drought with heat and salinity at the sensitive seedling stage. Sensitive genotypes (IR64, Pusa 1121, Gharib) recorded higher reactive oxygen species accumulation (20-40%), membrane damage (8-65%) and reduction in photosynthetic efficiency (10-23%) across the stress and stress combinations as compared to stress tolerant checks. On the contrary, N22 and Pokkali performed best under drought + heat, and drought + salinity combination, respectively. Moreover, gene expression pattern revealed the highest expression of catalase (CAT), ascorbate peroxidase (APX) and GATA28a in N22 under heat + drought, whereas the highest expression of CAT, APX, superoxide dismutase (SOD), DEHYDRIN, GATA28a and GATA28b in Pokkali under drought + salinity. Interestingly, the phenotypic variation and expression level of genes highlighted the role of different set of physiological traits and genes under drought and drought combination with heat and salinity stress. This study reveals that rice response to stress combinations was unique with rapid readjustment at physiological and molecular levels. Moreover, phenotypic changes under stress combinations showed substantial adaptive plasticity in rice, which warrant further investigations at molecular level.