Transcriptome Profiling of Abiotic Stress-Responsive Genes During Cadmium Chloride-Mediated Stress in Two Indica Rice Varieties

Rice growth and development is highly affected by the excessive concentration of the heavy metal cadmium (Cd). To elucidate the molecular basis of Cd tolerance, we carried out comprehensive transcriptome profiling of diverse groups of genes like those encoding antioxidative enzymes (APX, CAT, SOD, and GR), osmolyte-regulatory enzymes (P5CS, PDH, and BADH1), polyamine-regulatory enzymes (SAMDC, SPDS, SPMS, and DAO), transcription factors (TRAB-1 and WRKY-71), Osem and RbcS from leaf and root tissues under cadmium chloride (1.5 mM) stress at different time points (6, 12, and 24 h) of exposure in two indica rice varieties, that is, IR-64 (sensitive) and Nonabokra (tolerant). Analyses of massively parallel signature sequencing (MPSS) and publicly available microarray databases indicated the physiological role of the concerned genes and possible cross-talk between Cd and other abiotic stresses. Moreover, the pattern of expression, for a particular gene in leaves, varied in most cases from that in roots, suggesting a tissue-specific response. The higher accumulation of TRAB-1 transcript and protein in the tolerant cultivar Nonabokra in response to Cd stress suggested a role for TRAB-1 as a nodal component in Cd signaling pathway. Overall, the transcriptome analyses undertaken in the present study indicated that the genes, belonging to different functional classes and conferring Cd tolerance, were differentially regulated and mostly overrepresented under stress situations, thus providing novel insight into the functional basis of Cd tolerance in rice varieties and the importance of cross-talk of different signaling pathways. The present work will also pave the way in the future to select gene(s) for overexpression, so that rice can better tolerate Cd stress.