Functional Analysis Of Atypical NLR Protein TN13 In Plant Immunity In Arabidopsis Thaliana

Plant is characteristic of sessile growth and cannot escape pathogen attack by moving,so they have evoloved an innate immune system against the pathogen invasion.Nucleotide binding-leucine-rich repeat sequence(NLR)proteins can recognize the effectors from pathogens and play important roles in plant innate immunity.TIR-NBS(TN)protein which lacks the LRR domain,belongs to one type of atypical NLR,but the role of the TN protein in plant immunity is poorly understood.The well-characterized Arabidopsis typical CC-NBS-LRR(CNL)protein RESISTANCE TO PSEUDOMONAS SYRINGAE(RPS5)activates defense responses after recognizing Pseudomonas syringae type III effector Avr Pph B.However,whether other NLR proteins are required for RPS5-activated immune signaling is not clear.To investigate the function of TNs in plant immunity and whether they participate in RPS5-mediated resistance,we first examined the interactions of Arabidopsis TNs protein with RPS5 by a Split-Luciferase Complementation(LUC)assay.We found that TN13 and TN21 both can interact with RPS5.However,only the tn13-2 mutant,but not tn21-1,displayed enhanced susceptibility to Pseudomonas syringae pv.tomato(Pto)DC3000 avr Pph B;moreover,the tn13-2 mutant exhibited less susceptible response to Pto DC3000 avr Pph B compared to rps5-2 single mutant,suggesting that TN13 is only partially involved in RPS5-mediated resistance to Pto DC3000 avr Pph B.In addition,the regulation of Pto DC3000 avr Pph B resistance by TN13 appears to be specific,as loss of function of TN13 did not compromise resistance to Pto DC3000,Pto DC3000 hrc C–or Pto DC3000 avr Rpt2.Furthermore,the CC and NBS domains of RPS5 play essential roles in the interaction with TN13 by LUC and Co-immunoprecipitation(Co-IP)assays.Taken together,TN13 participates in RPS5-mediated immune pathway and may be act as a helper protein contributing to RPS5-activated resistance,indicating that TN-type NLR proteins function in CNL-mediated immune signaling,which reveals a new molecular mechanism for TN regulation plant immunity.