Mitogen-activated protein kinase(MPK) cascades consist of a set of kinase types(MPKKKs,MPKKs,MPKs) to establish conserved signal-transducing modules mediating plant growth,development as well as responses to internal and external cues.In this study,the expression patterns of six MPKKK,two MPKK,and 11 MPK genes in wheat in responses to external treatments of phytohormones,including naphthylacetic acid(NAA),abscisic acid(ABA),6-benzyladenine(6-BA),gibberellin(GA_3),salisylic acid(SA),jasmonic acid(JA),and ethylene(ETH),were investigated.Expression analysis revealed that several of the MPK cascade genes are responses to the external phytohormone signaling.Of which,TaMPKKKA;3is induced by 6-BA and NAA while TaMPK4 repressed by ETH,GA_3,SA,and JA;TaMPKKKA,TaMPKKKA;3 and TaMPK1 are down-regulated by ETH and GA_3whereas TaMPK9 and TaMPK12 repressed by ETH and JA in addition that TaMPK12 also repressed by GA_3;TaMPK12;1 is down-regulated by ABA,GA_3 and SA while TaMPK17 repressed by all exogenous phytonormones examined.TaMPK4,a MPK type gene previously characterized to mediate tolerance to phosphate(Pi)deprivation,was functionally evaluated for its role in mediation of responses of plants to exogenous GA_3,ETH,SA,and JA.Results indicated that overexpression and antisense expression of TaMPK4 in tobacco dramatically modify the growth of seedlings upon treatments of GA_3,SA and JA,in which the overexpressors behaved deteriorated growth feature whereas the seedlings with antisense expression of TaMPK4 exhibited improved seedling phenotype.The growth behaviors in lines overexpressing or antisensely expressing TaMPK4 are closely associated with the biomass and the corresponding hormone-associated parameters.These results demonstrated that TaMPK4 acts as a critical player in mediating the phytohormone signaling.Our findings have identified the phytohormone-responsive MPK cascade genes in wheat and provided a connection between the phytohormone-mediated responses and the MPK cascade pathways. Mitogen-activated protein kinase (MPK) cascades consist of a set of kinase types (MPKKKs, MPKKs, MPKs) to establish conserved signal-transducing modules mediating plant growth, development as well as responses to internal and external cues. In this study, the expression patterns of six MPKKK, two MPKK, and 11 MPK genes in wheat in responses to external treatments of phytohormones, including naphthylacetic acid (NAA), abscisic acid (ABA), 6-benzyladenine (6-BA), gibberellin Analysis of the MPK cascade genes are responses to the external phytohormone signaling. Of which TaMPKKKA; 3is induced by 6-BA (salicylic acid (SA), jasmonic acid (JA), and ethylene and NAA while TaMPK4 repressed by ETH, GA_3, SA, and JA; TaMPKKKA, TaMPKKKA; 3 and TaMPK1 are down-regulated by ETH and GA_3whereas TaMPK9 and TaMPK12 repressed by ETH and JA in addition that TaMPK12 also repressed by GA_3; TaMPK12; 1 is down-regulated by ABA, GA_3 and SA while TaMPK17 repressed by all exogen ous phytonormones examined.TaMPK4, a MPK type gene previously characterized to mediate tolerance to phosphate (Pi) deprivation, was functionally evaluated for its role in mediation of responses of plants to exogenous GA_3, ETH, SA, and JA.Results indicated that overexpression and antisense expression of TaMPK4 in tobacco dramatically modified the growth of seedlings upon treatments of GA_3, SA and JA, in which the overexpressors behaved deteriorated growth feature in the seedlings with antisense expression of TaMPK4 exhibited improved seedling phenotype. The growth behaviors in lines overexpressing or antisensely expressing TaMPK4 are closely associated with the biomass and the corresponding hormone-associated parameters. the results of which demonstrate that that TaMPK4 acts as a critical player in mediating the phytohormone signaling. Our findings have identified the phytohormone-responsive MPK cascade genes in wheat and provided a connection between the phytohormone-mediated responses and the MPK cascade pathways.