Functional Characterizations Of Septins In The Smoke Tree Wilt Fungus Verticillium Dahliae

The smoke tree wilt caused by Verticillium dahlia Kleb.poses a serious theat to red-leaf landscape in Beijing and other places.The smoke tree wilt is a kind of systemic plant disease,and the chemical treatments are extremely ineffective.The pathogens of the smoke tree wilt form microsclerotia with strong resistance during the late stage of the disease.There is no effective control measures for this disease.Microselerotia plays an extremely important role in the pathogenesis.It has great theoretieal and practieal significance to reveal the molecular basis of the formation mechanism of microsclerotia.Therefore,this study focused on the Septins of the smoke tree wilt by reverse genetics to clarify the mechanism of action of this gene falily in microsclerotia formation and pathogenesis.The research results were as follows:1)There are four Septins in Verticillium dahliae and named as VdSep3（VDAG₀0736）,VdSep4（VDAG₀7169）,VdSep5（VDAG₀4382）and VdSep6（VDAG₀1474）.2)Knockout of VdSep3,VdSep4 and VdSep6 resulted in a decrease in the conidia’s production of the mutant,however the conidia’s production of the mutant increased compared with the wild type after the VdSep5 gene is deleted.In addition,all Septins regulate the growth polarity of hyphae and the distribution and transport of chitin.3)VdSep3 negatively regulate the microsclerotia formation and melanin synthesis and the VdSep6 does the opposite,while VdSep4 and VdSep5 genes have little effect on microsclerotium formation and melanin synthesis.4)Deletion of VdSep4 gene enhances the resistance of Verticillium dahliae to chitin inhibitors,high osmotic stress and some pesticides,while the loss of the remaining three Septin family genes generally leads to decreased resistance to stress.It indicates that the Septins are involved in the response process of stress,but their division of labor is different.5)The deletion of VdSep3e VdSep4 and VdSep5 genes reduced the number of invasive nail formation,and the time and number of hyphae invasion into the host were delayed or decreased,which made the degree of tobacco disease inoculated with △VdSep3₂,△VdSep4₁ and △VdSep5₁ significantly lower than that of wild type strain.The deletion of VdSep6 caused the mutant to lose its ability to directly invade the host plant,indicating that the Septins is critical for the infection process of Verticillium dahliae.In conclusion,this study revealed that the Septins in Verticillium dahliae played important regulatory roles in the growth and development of mycelium,normal formation of microsclerotia,stress response and pathogenicity.Furthermore,based on the phenotype of each Septin mutant,it can be inferred that different Septins have different divisions within the cell.