Characterization and Expression Analysis ofNitrate Reductase 6-1ABDGene in Hexaploid Bread Wheat Under Different Nitrogen Regime

Abstract

AbstractNitrate reductase (NR) is the key rate-limiting enzyme of the nitrogen (N) assimilation process in plants, which has not been characterized in bread wheat under nitrogen stress, especially with respect to their homeologues. Total 9NRs were identified and classified into 3 groups, which showed a close relationship with different wheat ancestors. The occurrence of N-responsivecis-acting regulatory elements like MYB, MYC, G-Box and GATA-motif confirmed their N-responsiveness. Expression of all the three groups ofNRunder N-stress revealedNR 6-1ABDgroup to be the most N-responsive, which was characterized further in detail. The study was carried out in two genotypes contrasting for their N-responsiveness (HD 2967: Highly responsive to applied N, and Choti Lerma: Less responsive to applied N) selected on the basis of field evaluation. Homeologous differences within a genotype were found much more than the genotypic differences of a specific homeologue coding sequence. Among the three homeologues, thoughNR 6-1Dhomeologue was found most responsive to N-stress, the contribution was maximum for this homeologue followed byNR 6-1Aand least byNR 6-1B.We found that the expression of homeologues was linked to the presence of N-responsivecis-elements. All the homeologues ofNR 6-1in Choti Lerma were found less responsive to N-stress, in comparison to HD 2967, which might also be linked to N-use efficiency. Homeologous expression ofNR 6-1ABDrevealed negligible contribution ofB-homeologue to N-stress. Homeologous differences ofNR 6-1ABDwas found much more than the genotypic differences. Hence, our study on wheatNRwill be helpful in manipulating the specific homeologue of theNRgene in the future.