Characterization and expression analysis of mitogen-activated protein kinase cascade genes in wheat subjected to phosphorus and nitrogen deprivation, high salinity, and drought

Mitogen-activated protein kinase (MAPK) cascades are conserved signal-transducing modules that have important functions in plant growth and development as well as in diverse biotic and abiotic stress responses. In this study, six MAP kinase kinase kinase genes, two MAP kinase kinase genes, and 11 MAP kinase genes in wheat were characterized. The MAPK cascade members of wheat were named based on their homologs in Brachypodium distachyon and Arabidopsis. The polypeptides translated from these MAPK cascade genes share conserved domains similar to those reported in B. distachyon and Arabidopsis, and such domains are involved in protein interaction and phosphorylation. Expression analysis results of the MAPK cascade members revealed that some of the selected genes were involved in responses to phosphorus (P; ten genes) and nitrogen (N; five genes) deprivation, salinity (five genes), and drought (three genes). Such genes were either upregulated or downregulated. Temporal expression profile analysis of the stress-responsive MAPK members indicated that all of these genes were progressively regulated by stress and exhibited typical recovery responses when these genes were exposed again to normal growth conditions. Two MAPK members, TaMPK6 and TaMPK16, responded to four stress factors, including deprivations of P and N as well as salt and drought stress. TaMPK4, TaMPK12;1, TaMPK14, and TaMPK17 were responsive to two stress factors. These results suggested that various MAPK cascade members in wheat are involved in mediating signal transductions by transcriptionally regulating P and N deprivations, high salinity, and drought. TaMPK6 and TaMPK16, together with TaMPK4, TaMPK12;1, TaMPK14, and TaMPK17 have potential functions in mediating plant responses and tolerance to two or more stress factors by distinct MAPK cascade modules. Our data have provided information about MAPK modules and put further insight into their biological functions in abiotic stress response of wheat.