Studies On The Function Of Arabidopsis F-box Protein FB3 In Plant Immunity

Protein ubiquitination is one of the most important post-translational modifications of proteins and plays a fundamental role in maintaining cell homeostasis,normal cell physiology and many cellular functions.The ubiquitin-26 S proteasome system can alter the localization or activity of proteins,and even modify and degrade substrate proteins by ubiquitination.In the past two decades,it has been proved that the ubiquitin /26 S Proteasome system(UPS)can control the immune capacity of plants to cope with biological stress by regulating the level of plant hormones.E3 ubiquitin ligase determines the substrate specificity of UPS,and SCF E3 ubiquitin ligase is studied in depth.The F-box protein forms an SCF(SKP1-Cullin1-F-box)complex that determines the specificity of substrates degraded by SCF E3 ubiquitin ligase.In this study,a new F-box protein FB3 was found to regulate plant defense against pathogens in Arabidopsis thaliana.The results are as follows:1)FB3 is a new F-box protein.Bioinformatics analysis showed that the encoding protein was 275 aa,containing f-box motif at n-terminal but no substrate binding domain WD40 and LRR.FB3 belonged to FBXO protein family.Yeast two-hybrid experiments demonstrated the interaction between FB3 and S-phase kinase-associated protein 1(ASK1),confirming that FB3 was an F-box protein involved in the construction of SCF complex.2)FB3 locates in the nucleus and cytoplasm.Subcellular localization found that FB3 was expressed in the nucleus and cytoplasm.Similarly,plant tissue localization found that FB3 was widely present in plants.The size of FB3 was about 57 k D in the nucleus and 180 k D in the cytoplasm.3)FB3 is involved in extracellular immunity of Arabidopsis thaliana to Pseudomonas syringae pv.tomato DC3000(Pst DC3000).It was found that Pst DC3000 induced up-regulation of FB3 expression in wild type Arabidopsis thaliana within 24 h,and Pst DC3000 induced the strongest expression at 12 h.FB3 mutant was more susceptible after injection of Pst DC3000.4)FB3 regulates plant resistance through the JA pathway.Methyl jasmonate(Me JA)and Coronatine(COR)released by Pst DC3000 can simulate the up-regulated expression of FB3 induced by JA-lle,the active substance of Jasmonic acid(JA)in Arabidana.FB3-1 was more sensitive to Me JA and inhibited root growth.5)FB3 participates in the transmission process of plant immune signals,and FB3 regulates the cascade signal transmission of Mitogen-activated protein kinases(MAPKs)in plants.MAPK cascade assay showed that the intensity and duration of MAPK cascade induced by flg22 in mutant FB3-1 decreased.In conclusion,we found that FB3 regulates plant responses to biological stress.FB3 regulates plant resistance to Pst DC3000,FB3 can regulate MAPK cascade reaction to control defense signal transmission during plant immune response and mediate JA signal transduction in the process.This not only finds the new function of FBXO protein in plant disease resistance,but also is expected to reveal the potential pathway in plant disease resistance,and deepen the study of ubiquitin pathway on plant immunity.