The Small GTPase FgArl1 Participates In Growth,Development And Pathogenicity In Fusarium Graminearum

Wheat scab（Fusarium head blight,FHB）is one of the important diseases on wheat and other related crops,which seriously reduces the quality and yield of crops on a global scale,and bring huge economic losses.Under the influence of climate change,farming system and other factors,the incidence of the disease showed a trend of increasing year by year.F.graminearum is one of the main pathogens of wheat scab.It can produce deoxynivalenol（DON）,which can cause serious pollution to grain and seriously endanger the life and health of human beings and animals.Therefore,the study on the growth and development and pathogenic mechanism of F.graminearum is a vital prerequisite for the prevention and control of wheat scab.Vesicle transport is one of the most basic physiological processes of cell survival in eukaryotes.Studies have shown that many regulators of vesicle transport are related to the pathogenicity of fungi.In Saccharomyces cerevisiae and mammalian cells,the small GTPase Arl1 and its homologous proteins regulate vesicle transport,cytoskeleton recombination and other important biological processes.However,the Arl1 protein in F.graminearum has not been reported.In this study,we identified an Sc Arl1 homologous protein XP＿011326587.1 from F.graminearum PH-1 database.This protein（named Fg Arl1）is encoded by the gene FGSG＿06920.It was found that Fg Arl1 was located on the trans-Golgi network（TGN）.After the mutants were obtained by gene knockout,we studied the vegetative growth and development,pathogenicity and the activity of small GTPase in order to reveal the mechanism of Fg Arl1 on the growth,development and pathogenicity of F.graminearum.The main results are as follows:（A）The small GTPase Fg Arl1 regulates growth and development in F.graminearum1.The small GTPase Fg Arl1 regulates vegetative growth in F.graminearumCompared with the PH-1,the colony diameter ofΔFgarl1 decreased by about 25%,10%,26%and 20%respectively on CM,V8,5×YEG and MM medium,and the height of aerial hyphae decreased by about 26%.It was observed that more than 9%of the mycelium of WT and supplementary strain had extensive branching,but more than 74%inΔFgarl1.2.The small GTPase Fg Arl1 regulates asexual reproduction in F.graminearumIn terms of spore germination,the conidia germination rate of wild type（WT）and supplementary strains was as high as 85%in 3 h,while the conidia germination rate of the mutantΔFgarl1 was only about 5%.As for spore yield,WT and supplementary strain was basically the same,but the spore yield ofΔFgarl1 decreased by about 29%.Also,the mutantΔFgarl1 did not affect the sexual reproduction in F.graminearum.3.The small GTPase Fg Arl1 regulates the response of F.graminearum to different environmental stressesThe resistance ofΔFgarl1 to osmotic（KCl,Na Cl and Sorbitol）and oxidative（H₂O₂）was increased,but to cell wall stress（SDS and CR）was decreased significantly.（B）The small GTPase Fg Arl1 regulates the full virulence in F.graminearumCompared with the PH-1,the pathogenicity ofΔFgarl1 in wheat coleoptile and wheat spike at flowering stage decreased by about 50%,the content of DON decreased by about 37%,and the gene expression of TRI decreased by about 50%.The mutantΔFgarl1 could not completely block the formation of toxisomes,but significantly decreased the number of toxisomes after induction with TBI for 48 hours.（C）The activity of small GTPase Fg Arl1 is important for the growth,development and pathogenicity in F.graminearumGTP-binding Fg Arl1(Fg Arl1^Q71L)plays an important role in the vegetative growth and pathogenicity in F.graminearum.However,the GDP binding form of Fg Arl1^N126I and myristoylation-defective form Fg Arl1^G2A cannot rescue the phenotypic and pathogenic defects of the mutantΔFgarl1.In summary,these results suggest that Fg Arl1 plays an important role in the normal vegetative growth,development and pathogenicity,and affects the biosynthesis of DON by affecting the formation of toxisomes in F.graminearum.