Soybean Mapk Kinase Pathway And Soybean Defense Response

Mitogen-activated protein kinase(MAPK)cascade system is one of the highly conserved signal transduction pathways in eukaryotes.The typical MAPK cascade system consists of three protein kinases,MAPKKK,MAPKK,and MAPK,and they transmit signals recognized by the plasma-membran-localized receptors through sequential phosphorylation of MAPKKK-MAPKK-MAPK.The activated MAPKs can phosphorylates transcription factors,which leads to reprogramming of transcriptome.Therfore,MAPK cascade plays an important role in resisting invasion of pathogens.To determine the effect of GmMEKK1 silencing on different GmMPK activations and identify the GmMPK acting downstream of GmMEKK1,soybean GmMEKK1 was silenced using a bean-pod mottle-induced gene silencing technique(BPMV-VIGS)and the kinase activations of MPK3/4/6 was specifically detected by Western Blotting using Phospho-p44/42 MAP Erk1/2 antibody that can recognize the phosphorylated forms of MPK3/4/6 in plants.It was found that silencing GmMEKK1 reduced the activation of MPK6,and enhances the activation of MPK3 in response to flg22 treatment.Similar effect on MPK3/6 was also observed for the GmMPK4-silenced plants,suggesting that GmMEKKK1 and GmMPK4 may function in the same linear pathway.Meanwhile,we also found that GmMPK3 and GmMPK6 functionally compensated for each other.Because silencing one would result in the enhanced activation of the other.In Arabidopsis,MPK4 functions downstream of MEKK1 and the activation of MPK4 is abolished in mekk1 mutant plants.However,unlike in Arabidopsis,the activation of MPK4 was readily detectable either by flg22 or salicylic acid(SA),the activation of GmMPK4 was not detectable regardless of time and concentrations of flg22 and salicylic acid(SA)treatments or the methods used for detection of kinase activation.Therefore,it is unclear whether GmMPK4 acts downstream of GmMEKK1,suggesting that a significant difference in MPK4 activation between soybean and Arabidopsis.