Understanding The Roles Of Soybean Recptor-like Kinase GmFLS2 And Its Co-receptor GmBAK1 In Disease Responses Through Virus Induced Gene Silencing (VIGS) Mediated By Bean Pod Mottle Vrius(BPMV)

The plasma membrane(PM)-localized receptor-like kinaes(RLKs)play important roles in growth,development,and pathogen defense.The first cloned RLK is the Arabidopsis receptor kinase FLS2(FLAGELLIN SENSING 2),which specifically recognizes a conserved 22 amino acid N-terminal sequence of bacterial flagellin protein(flg22).BAK1(BRI1-ASSOCIATED KINASE1)is a coreceptor of FLS2,which forms a dimer with FLS2 or other PRRs and is required for activation of downstream signaling.Although extensively studied in Arabidopsis,the functions of RLKs in crop plants remain largely uninvestigated.To understand the roles of RLKs in soybean,we silenced GmFLS2 and GmBAK1,respectively,via virus induced gene silencing(VIGS)mediated by Bean pod mottle virus(BPMV).The reduced transcript levels of GmFLS2 and GmBAK1 in the silenced plants were confirmed by RT-PCR.No significant morphological differences were observed between GmFLS2-silenced plants and the vector control plants.However,the GmBAKl-silenced plants were significantly stunted,and severe necrosis or HR(Hypersensitive response)cell death was observed on the leaves and stems of the GmBAK1-silenced plants.The GmBAK1-silenced plants died after 30 days post inoculation(dpi),suggesting that GmBAK1 plays key roles not only in normal growth and development but also in regulation of cell death in soybean.Similar in Arabidopsis,silencing GmFLS2 or GmBAKl enhanced the sensitivity of the soybean plants to Xanthomonas campestris pv.glycines(Xag)and Pseudomonas syringae pv.glycinea(Psg),respectively,suggesting that the functions of GmFLS2 and GmBAK1 are conserved in immunity against bacteria across different plant species.Unexpectedly,silencing GmBAKl enhanced the resistance of soybean plants to Soybean mosaic virus(SMV),indicating that it plays opposite roles in antibacterial and antiviral immunities.Finally,kinase activity assay showed that silencing GmFLS2 significantly reduced the activation of GmMPK6 in response to flg22 treatment,implying that defense response is transduced through activation of GmMPK6-mediated signaling pathway upon recognition of pathogens by GmFLS2.Our studies lay a solid foundation for revealing the roles of GmFLS2 and GmBAK1 in defense responses in soybean.