The Role Of GmBIR1 In Cell Death And Immune Defense Response

Receptor-Like kinases?RLKs?are a huge group of Pattern Recognition Receptors,and play a critical role in recognizing pathogens,transducing defense signals,and activating immune defense;Although extensively studied in model plants arabidopsis and rice,the studies of the RLKs in crops including soybean are still limited.Soybean is a paleotetraploid plant with gene redundancy.The traditional forward genetic approaches are not suitable for gene function studies of soybean.Therefore,we used reverse-genetic strategy mediated by BPMV?Bean pod mottle virus?-induced gene silencing?BPMV-VIGS?to explore the roles of Gm RLKs in soybean immunity.A Gm RLK playing negative roles in cell death and immunity was identified through a high throughput screening of RLKs in soybean using BPMV-VIGS.Because this RLK shares the highest homology with BAK1-interacting receptor-like kinase?BIR1?,we thus named it as GmBIR1.Silencing GmBIR1 in soybean resulted in a phenotype reminiscence of constitutively activated defense responses including a stunted stature with massive observable cell death on the leaves of the silenced plants,which was subsequently confirmed by trypan blue staining.Consistent with this phenotype,GmBIR1-silenced plants exhibited significantly enhanced resistance to both Pseudomonas syringae pv.glycinea?Psg?and Soybean mosaic virus?SMV?,two different types of pathogens,compared with the vector control plants,further confirming that GmBIR1 is a negative regulator of disease resistance in soybean.Salicylic acid and H₂O₂are inducers of cell death and immune responses.DAB staining of H₂O₂and HPLC quantification of SA indicated that both SA and H₂O₂were over-accumulated on the leaves of the GmBIR1-silenced plants compared to the vector control plants,implying that the cell death and constitutive activated defense responses we observed in silenced plants could be resulted from over-accumulated SA and H₂O₂.In addition,even though GmBIR1 positively regulated the activation of Gm MPK3/6,cell death and constitutive activated immune response observed in the GmBIR1-silenced plants is independent of Gm MPK3/6.Taken together,our results indicated that the cell death and constitutive activated defense response observed in the GmBIR1-silenced plants are related to the over-accumulation of SA and H₂O₂,so GmBIR1 plays a negative role in immune defense response.