Transcriptional regulation of ABA core signaling component genes in sorghum (Sorghum bicolor L. Moench)

Abscisic acid (ABA) plays an important role in growth, development and adaptation of plants to environmental stresses. The mechanism of ABA signal transduction involves three core components namely ABA receptors [pyrabactin resistance 1 (PYR1)/PYR1-like (PYL)/regulatory component of ABA receptor (RCAR)], clade A PP2Cs and Class III SnRK2 family proteins. In the present study, we identified and analyzed the core components of ABA signaling in sorghum, which is known for its drought tolerance. Genome wide in silico analysis led to the identification of eight PYL ABA receptors, nine clade A PP2Cs and three class III SnRK2 family members. Abiotic stresses and exogenous ABA-mediated transcriptional changes of the genes encoding ABA core signaling components were analyzed at seedling stage. All the members of SbPYL gene family were downregulated, except SbPYL1 and SbPYL7 which showed significant upregulation in leaf under drought stress. SbPYL1 and SbPYL5 were upregulated in response to ABA, cold, high salt and PEG-induced osmotic stress, while SbPYL4 showed significant upregulation only under cold stress. Expression levels of the SbPP2C genes were higher or unaffected in response to exogenous ABA and abiotic stresses in leaf except SbPP2C5, which decreased under cold stress. SbPP2C4, SbPP2C5 and SbPP2C6 were highly induced (up to 56-fold-99-fold increase) under different stresses. Expression of class III SbSnRK2 genes was either unaffected or downregulated under abiotic stresses and exogenous ABA. Heat stress downregulated the expression of all the ABA core signaling component genes except that of SbPP2C6 which was upregulated under heat stress. In general, abiotic stresses upregulated the expression of PP2Cs but downregulated the expression of SnRK2 in sorghum seedlings. Differential stress-responsive expression and less number of PYLs in sorghum as compared with Arabidopsis suggest that SbPYL family members might have acquired distinct functions during evolution.