Functional Analysis Of Histone Acetyltransferases Genes In Fusarium Graminearum

Fusarium head blight(FHB)caused by Fusarium graminearumis an important fungal disease of grain crops,widely distributes around the world,and it does harm to wheat production.The most important thing is,large amount of deoxynivalenol(DON)produced by Fusarium graminearum can be retained in wheat and wheat products.Which seriously damage the health of human and domestic animal,resulting in food security problems.The biosynthesis of DON is mediated by TRI gene cluster.Previous study shows that the expression of genes have consistency in cluster,and is closely related to epigenetic regulation.Histone acetylation modification is an important mechanism of epigenetic regulation,however,there has been no reports of histone acetylation modification regulation of secondary metabolic pathways in Fusarium graminearum.In order to learn about the function of histone acetylation modification in secondary metabolic pathway and pathogenesis process,we have identified nine histoneacetyltransferase genes in Fusarium graminearum,including HAT1,GCN5,TAF1,ESA1,SAS3,SAS2,ELP3,HPA2/HPA3 and RTT109.We tried to knock them out and got the corresponding mutants except TAF1 and ESA1.So we determine them as lethal genes.gcn5,sas3,elp3 mutants were reduced in aerial hyphae and growth rate.gcn5 mutant failed to produce conidia.sas3 and elp3 mutants can produce longerconidium while rtt109 produce shorter conidium than wild type.Lack of GCN5 and SAS3 completely blocking the sexual development.Rtt109 mutant can produce smaller perithecia which blocked in ascus formation.Pathogenicity of gcn5,sas3,elp3 and rtt109 mutants reduced significantly.gcn5,sas3,hat1 and elp3 mutants seriously reduced in DON synthesis.Exogenous cAMP can restore the DON synthesisof hat1 and elp3 mutants but not gcn5 and sas3 mutants.Showing that the two genes may be the downstream of cAMP signaling pathways.This study is focused on the relationship betweenSAS3 and cAMP-PKA signal pathway and find its downstream target genes.We examined the gene expression of pka and sas3 mutants in different nutrition condition by RNA-seq analysis.Under the nutrient sufficiency symptom,lack of PKA led to 1807 genes down-regulated while sas3 mutant has 1232 genes down-regulated,and there are 856 overlapping genes inpka and sas3 mutant.Under the nutrient deficiency symptom,lack of PKA has 1287 down-regulated genes while sas3 mutant has 246 down-regulated genes,and there are 190 overlapping genes between pka and sas3 mutant.Gene function enrichment analysis shows that the overlapping genes exist in many secondary metabolism related genes,indicated that PKA and SAS3 have intimate interaction and both of them are involved in regulation of secondary metabolism.Phosphorylation data shows there are four phosphorylation sites in Sas3,two of them have marked characteristic of PKA phosphorylation sites.When do the mutantion of the potential PKA phosphorylation sites in Sas3,the SAS3-SA strain restored only half in pigmentation,conidiation and sexual reproduction,while toxin-producing has not recovered,indicated that it`s important for Sas3.In addition,to explore the relationship of SAS3 and the other acetyl transferase genes,acetyl transferase genes knocked out respectively on the background of sas3 mutants.which proved that Sas3 has overlapping functions with Gcn5,Rtt109 and Elp3.Comprehensive the above results,we think PKA can phosphorylate Sas3 to regulate histone acetylation level and further regulate expression of secondary metabolism gene clusters,and finally affect growth,development and metabolism of Fusarium graminearum.