Investigation Of Receptor Kinase StLRPK1,StSERK3A/BAK1 And Phosphotase StBSLs Functions In Potato Immunity Against Late Blight

China is the country with largest potato?Solanum tuberosum L.?planting area.Potato plays crucial role in agriculture and economy in China.Phytophthora infestans?Mont.?de Bary caused late blight is the most devastating disease resulted in the serious losses of potato production in field.The ultilise of chemical fungalcide is the major measure to prevent late blight invasion,but excessive use of unfriendly environmental chemicals increases the costs of potato and the risks of food safety.The exploration and understanding on molecular mechanisms of potato resistance is the theoretical basis for exploring and developing effective methods for control of late blight.In this study,we investigated the function and molecular mechanism of receptor kinase StLRPK1 in potato resistant to P.infestans and co-receptor StSERK3A/BAK1 function in Pep-13 trigger innate immunity and in potato resistant to P.infestans.We also reported the roles of P.infestans effector PiAVR2 targets StBSL1,StBSL2 and StBSL3 in plant immunity and in the recognition of PiAVR2 and R2.The main results are listed as follows:1.StLRPK1 belongs to the STRUBBELIG RECEPTOR FAMILY?SRF?subfamily and localizes at plasma membrane.StLRPK1 responds to P.infestans culture filter treatment,but does not change with flg22 treatment,compared with their corresponding controls?P.infestans liquid medium and H₂O treatment,respectively?.2.StLRPK1-GFP was immunoprecipitated with StSERK3A/BAK1-cMyc or NbSERK3A/BAK1-cMyc,but was not with control cMyc-StBSL1.The silencing of NbSERK3A/BAK1 resulted in significant compromise of StLRPK1 overexpression transgenic N.benthamiana resistant to P.infestans.In addition,the silencing of MEK2/WIPK also weaken StLRPK1 resistant to P.infestans.Therefore,StLRPK1-mediates resistant to P.infestans dependents on SERK3A/BAK1 and activates MEK2/WIPK MAPK cascade.3.The silencing of StSERK3A/BAK1 compromises potato resistant to P.infestans,but is not involve in Pep-13 triggered plant innate immunity.Up-regulation expression of PTI marker genes stimulated by SERK3A/BAK1 independent MAMPs resultes from the significant decrease of transcript expression level of BR pathway marker genes CHL1,EXP8,CAB50 and STDH in SERK3A/BAK1 silenced potato.4.StBSL1,StBSL2 and StBSL3 are PiAVR2 targets,as susceptibility factors in plant immunity.Overexpression of GFP-StBSL1,GFP-StBSL2 and GFP-StBSL3 pronouncedly accelerated P.infestans colonization in N.bethamiana.NbBSL2 and NbBSL3 silenced N.bethamiana performed more resistant to P.infestans.The surpression of INF1 induces cell death by GFP-StBSL1 and GFP-StBSL3 relys on a bHLH transcript factor CHL1 that is involved in BR signaling pathway.5.StBSL1,StBSL2 and StBSL3 performes similar roles in the recognition of R2/PiAVR2 or R2/Pi21645.Overexpression of GFP-StBSL1 significantly accelerated PiAVR2/R2 trigger HR,Pi21645/R2 induce HR showed the similar trend but not siginificant difference.Transient expression of GFP-StBSL2 and GFP-StBSL3 strikingly suppressed PiAVR2/R2 and Pi21645/R2 mediate HR.PiAVR2/R2 and Pi21645/R2 induce HR compromised in NbBSLs silenced lines.6.Phosphotase mutant StBSL1H764V abolishes phosphotase activtiy of StBSL1.Coexpression GFP-StBSL1H764V with PiAVR2/R2 resulted in suppression of PiAVR2/R2trigger HR.Western blots assay showed that GFP-BSL1 interacts with cMyc-StBSL1 and cMyc-StBSL1H764V,while GFP-PiAVR2 does not associate with cMyc-StBSL1H764V.So we conclued that StBSL1 phosphotase activtiy and homodimerization are required in the recognition of PiAVR2 and R2.7.The stability of cMyc-BSL1 was reduced by GFP-StBSL2 or GFP-StBSL3 in presence of PiAVR2,and the interaction of GFP-PiAVR2 and cMyc-StBSL1 weaken by GFP-StBSL2.