Heat Stress Tolerance Gene FpHsp104 Affects Conidiation And Pathogenicity Of Fusarium Pseudograminearum

In recent years,Fusarium crown rot(FCR)caused by Fusarium pseudograminearum is widely distributed in the Huanghuai wheat-growing region of China.The brown stem base and whiteheads caused by F.pseudograminearum,lead to serious loss of wheat yield.F.pseudograminearum also produces mycotoxins during its infection,which is a serious threat to people’s health.Symptoms hiding,lack of disease-resistant wheat varieties,and shortage of effective fungicide led to FCR being difficult to control.Molecular mechanism studies of fungal pathogens have theoretical and practical significance for the selection and breeding of resistant varieties,exploitation of resistant resources,and drug targets selection of this disease.Thermotolerance plays an important role in the survival,distribution,and pathogenicity of fungi.Studies have shown that eukaryotes tend to induce a highly conserved process,heat shock response,in response to high temperatures.Heat shock proteins(Hsps)are widely existing in bacteria to mammals,which play an essential part in biological resistance.In particular,the Hsp100 family plays a key role in the high temperature and other various chemicals tolerance in bacteria,Saccharomyces cerevisiae,and plants.However,their functions remain largely unknown in plant fungal pathogens.In this study,a conserved Hsp100 encoding gene FpHsp104 was identified in F.pseudograminearum,and it encodes a103.07 k Da protein.FpHsp104 contains two AAA domains that are highly conserved in fungi.The expression levels of FpHsp104 were relatively stable in mycelia and the infection stages.Deletion of FpHsp104 did not affect the growth and mycelia morphology.After hightemperature treatment,the WT and Δfphsp104-C strains could recover after 2 days of the optimal temperature,but the Δfphsp104 was not.Furthermore,the death rate of Δfphsp104conidia after heat shock was higher than that of WT and Δfphsp104-C.The FpHsp104-GFP showed dynamic localization to small particles under high temperature.These results suggest that FpHsp104 is critically required for thermotolerance of F.pseudograminearum.In F.pseudograminearum,the expression level of FpHsp104 was significantly upregulated in conidia.Compared with WT and Δfphsp104-C,the conidia production ofΔfphsp104 was decreased significantly,and the conidia became shorter and less separated.The expression levels of key conidiation-genes FpFlu G,FpVos A,and FpAba A were significantly downregulated in Δfphsp104.But the m RNA splicing repair in Δfphsp104 strain was not affected after heat treatment.In addition,the conidial germination rate of Δfphsp104was slower than that of the WT and Δfphsp104-C,but the ability of conidial germination was not affected.Deletion of FpHsp104 significantly reduced the pathogenicity of F.pseudograminearum,but did not affect the DON production.However,FpHsp104 deletion of F.pseudograminearum showed a null response to osmotic stress,oxidative stress,and cell wall stress.The transcription factors FpCsm1 and FpNot2 were found to be involved in the thermotolerance by screening from the previously obtained mutants of F.pseudograminearum.Compared with WT and Δfpcsm1-C,the ability of Δfpcsm1 to recover mycelia growth after heat shock is enhanced,and the recovery time of FpHsp104 expression was advanced.It is suggested that FpCsm1 might be involved in heat tolerance of F.pseudograminearum by regulating the expression of FpHsp104.Except for the thermotolerance,FpCsm1 also negatively regulated conidia production,and positively regulated the pathogenicity of F.pseudograminearum.Compared with WT and Δfpnot2-C,Δfpnot2 was more sensitive to high temperature,but the expression of FpHsp104 was no significant difference in the mutant..It showed that FpNot2 might affect the heat tolerance of F.pseudograminearum in other ways.Meanwhile,the loss of FpNot2 reduced the pathogenicity of F.pseudograminearum,but the production of DON and ZEN toxins were significantly increased.