Identification Of Effectors And Research Of SIX8 Functions In Pathogenicity Of Fusarium Oxysporum F.sp. Cubence Tropical Race 4

Banana(Musa nana Lour.)is a monocot perennial herbaceous fruit,which belongs to Musaceae Juss family,Musa genus.Banana is the world’s fourth largest food crop.In 2009,its total output surpassed citrus and became the world’s No.1 fruit in total yield.Banana wilt disease is a soil-borne disease caused by Fusarium oxysporum f.sp.cubense.The major causal agent of banana wilt disease in Hainan is Fusarium oxysporum f.sp.cubense race 4(Foc4).In this study,the involvement of the transcription factor SGE1 in the regulation of effectors synthesis in Foc4,the pathogenic mechanism of effector SIX8,the effect of Fimbrin on effector secretion,and the synergetic effects between the three of them were investigated.And the main results were as follows:1.The SGE1 overexpression strain Foc4-ΔSGE1 OE was constructed.A total of 919 proteins were identified by Lable Free proteomics for extracellular secreted proteins,and a total of 74 candidate effectors regulated by SGE1 were predicted,of which 37 effectors were up-regulated and 17 effectors were down-regulated.The expression of 11 effectors did not change significantly,and the abundance of 9 effectors were extremely low.In addition,24 proteins were identified as cellulase,pectinase and lipase.The promoter regions of those candidate effectors and the SIX effectors family were analyzed,and the results showed that there were other mechanisms involved in regulation of the SIX genes besides being regulated by SGE1.SGE1 promotes the vegetative growth and colonization,while inhibits necrotrophy of Foc TR4.2.The knockout strain Δfimbrin was generated;Δfimbrin has showed impaired pathogenicity to Brazilian bananas,slowed mycelial growth rate,reduced conidia production,and reduced conidia germination rate.The secretion of candidate 41 effectors was affected by the absence of Fimbrin,among them,the abundance of 17 effectors were up-regulated,and the abundance of 24 effectors were down-regulated.In addition,three other proteins have been identified as pectinase and lipase.Compared with the extracellular proteins of overexpression strain Foc4-ΔSGE1 OE,9 effectors are shared by the extracellular proteins of these two strains,indicated that these 9 effectors are regulated by SGE1 and are secreted to the Foc4 extracelluar space to function by Fimbrin-involved vesicle transportation.3.A banana yeast-two-hybird cDNA library was constructed,and Ma PR6,a protein that interacts with SIX8,was screened.The transcriptome of banana roots was sequenced underΔSIX8 and ΔSGE1 treatments.Among them,most genes were only regulated by SIX8,indicating that these genes can specifically recognize SIX8 when banana roots were infected by Foc4.SIX8 can activate certain transcription factors to activate the transcription and translation of PR6 after Foc4 infects bananas to secrete SIX8,and then PR6 interacts with SIX8.SIX8 may participate in the regulation of Ma PR6 expression through some mechanism and interact with it.Our results revealed some mechanisms of effectors in regulation of pathogenicity of Foc4,and provided some clues for controlling banana wilt disease.