A multi-step phosphorelay two-component system impacts on tolerance against dehydration stress in common wheat

Wheat is an important staple crop, and its productivity is severely constrained by drought stress (DS). An understanding of the molecular basis of drought tolerance is necessary for genetic improvement of wheat for tolerance to DS. The two-component system (TCS) serves as a common sensor-regulator coupling mechanism implicated in the regulation of diverse biological processes (including response to DS) not only in prokaryotes, but also in higher plants. In the latter, TCS generally consists of two signalling elements, a histidine kinase (HK) and a response regulator (RR) associated with an intermediate element called histidine phosphotransferase (HPT). Keeping in view the possible utility of TCS in developing water use efficient (WUE) wheat cultivars, we identified and characterized 62 wheat genes encoding TCS elements in a silico study; these included 7 HKs, 45 RRs along with 10 HPTs. Twelve of the 62 genes showed relatively higher alterations in the expression under drought. The quantitative RT-PCR (qRT-PCR)-based expression analysis of these 12 TCS genes was carried out in wheat seedlings of a drought sensitive (HD2967) and a tolerant (Dharwar Dry) cultivar subjected to either dehydration stress or cytokinin treatment. The expression of these 12 genes under dehydration stress differed in sensitive and tolerant genotypes, even though for individual genes, both showed either up-regulation or down-regulation. In response to the treatment of cytokinin, the expression of type-A RR genes was higher in the tolerant genotype, relative to that in the sensitive genotype, the situation being reverse for the type-B RRs. These results have been discussed in the context of the role of TCS elements in drought tolerance in wheat.