Coetaneous activity of Sub1a and SK for maintenance of underwater growth in rice genotypes

Despite the availability of flood-tolerant genotypes with Sub1a-mediated elongation, SK has been depicted as the primary gene responsible for elongation under prolonged submergence. However, the combined role of both loci (Sub1a and SK) are prerequisites for the survival of rice plants under flash floods followed by stagnant floods that are yet to be revealed. The combinatorial action of Sub1a and SK in a selected group of lowland rice with the simultaneous presence of both loci were studied for their physio-biochemical performance under induced flash flood followed by water stagnation for 21 days. Among the lines, var. Ganga Sali showed elongation and Kalapatia showed quiescence growth with varied degrees of aerenchyma formation. Further, it was endorsed that var. Ganga Sali showed the highest enzymatic activity of ADH and minimal for PDC under submerged conditions. RT PCR-based expression analysis of Sub1a, SK1, SK2, adh1, pdc1, and susy1 genetic loci under differential submergence showed a mixed response to the depth and duration of the induced flood, among which Sub1a and SK2 showed distinct differences between normal and test plant tissue. From expression analysis, the differential activity of Sub1a and SK2 was recorded, which showed that during the onset of flood, Sub1a starts to express in both the var. Ganga Sali and var. Kalapatia, but as the flood prevails for a longer period, the expression of Sub1a is masked by both SK1 and SK2. Overall, the study demonstrates the combinatorial role of both the genes in two studied rice lines under different flood regimes and their effect on phenotype. The present work may be the first report on the combinatorial expression of Sub1a and SK under differentially induced submergence on a mixed rice population.