Regulation of expression of genes associated with nitrate response by osmotic stress and combined osmotic and nitrogen deficiency stress in bread wheat (Triticum aestivum L.)

In drought prone areas, often farmers use less nitrogen, and thus the crop is subjected to combined stress (low N+osmotic stress). Since understanding the regulation of genes involved in nitrate signalling, uptake and assimilation under water-deficit (osmotic stress) is important for improving yield under the combined stress environments, this study analysed the regulation of genes coding for N responses under low N, osmotic stress (OS) and combined stress conditions in seedlings of a wheat. The results revealed that HD2967, a mega wheat variety, was more tolerant to short-term N starvation, OS and combined stress as compared with C306, a drought tolerant check. Interestingly, it was found that low N stress can also lead to accumulation of ABA in wheat seedlings. Real-time RT-qPCR analysis revealed that in addition to low N stress, OS also regulated expression of nitrate signalling genes (TaCIPK8, TaCIPK23, TaNLP4, TaSPL9, TabHLH1 and TaNAC4), HATS gene TaNRT2.1, LATS genes (TaNRT6.5 and TaNPF7.1), nitrate and nitrite assimilation genes and ammonium assimilation genes at least in one tissue of one of the genotypes. Combined stress was found to have significant interaction in regulation genes for nitrate signalling, uptake and assimilation. TabZIP1 and TaPIMP1 TF were identified as new players in low N response in wheat. Thus, osmotic stress and combined stress modulates the genes for N responses, and genotypic variation exists for this in wheat. The common expression pattern of N response genes found under low N and OS may probably regulated, at least in part, by ABA-dependent pathway, as ABA accumulation was induced by both OS and low N stresses. Functional analysis of the osmotic stress regulated genes coding for N response will help enhance tolerance of wheat to combined stress conditions.