Physiological Mechanism Of Brassinolides In Alleviating High Temperature Stress At Flowering Stage In Rice And Regulatory Function Of HXK1 And CREA In Fusarium Proliferatum

In recent years,high temperature stress and rice spiklet rot disease(RSRD)have caused serious losses to rice yield.At present,BRs have been widely studied in biotic and abiotic stresses.However,its effects on alleviate the damage caused by high temperature stress in rice and prevention of RSRD remains obscure.This study intends to investigate whether it can alleviate the damage caused by high temperature stress in rice by spraying EBR,and its effects on prevention of RSRD.In this study,seed setting rate,pollen activity and anther dehiscence significantly decreased under high temperature stress,while seed setting rate,anther dehiscence increased by 23.09% and 55.4%,and pollen activity of rice middle and lower parts of spikelet increased by 8.64% and 24.2% after spraying EBR.The activities of SOD,POD,CAT were significantly reduced under high temperature stress,but EBR treatment could significantly increase the activity of SOD by 51.76% and also greatly increased the accumulation of proline and soluble sugar under high temperature stress,which was helpful to alleviate damage.Under high temperature stress,the endogenous hormone ABA content increased,GA content decreased,while by spraying EBR,the ABA content further increased by 4.78%,and GA content decreased by 8.71%,the results indicated that EBR treatment can alleviate the damage of high temperature in rice by regulating the changes of endogenous hormones.However,spraying EBR had no significant effect on the disease index of RSRD.In order to provide a theoretical basis for the prevention of RSRD,gene function of HXK1 and CREA in Fusarium proliferatum(the dominant pathogen of RSRD)were studied.The main findings are as follows:Our results on HXK1 in F.proliferatum showed that FBP1 and TPS1 gene expression in the △hxk1 deletion mutant was down-regulated,while HXT3,PEPCK,and FBP1 were up-regulated when compared to the wild type.This revealed that the △hxk1 mutant both compensated for defective glycolysis by increasing sugar transport and gluconeogenesis efficiencies and affected the trehalose synthesis pathway.What’s more,the △hxk1 mutant exhibited reduction of sporulation and inhibited mycelial growth rate.The △hxk1 mutant showed impaired growth on sugars and was strongly suppressed in the presence of fructose,indicating that HXK1 has a special role in sugar utilization.Furthermore,the △hxk1 mutant not only showed increased sensitivity to Congo red and SDS,but also increased sensitivity to NaCl and KCl,thus suggesting that HXK1 is involved in cell wall integrity.Additionally,the results of a plant infection assay showed that rice inoculated with △hxk1 could reduce infected,thus indicating that HXK1 contributes to virulence.Therefore,HXK1 is likely required for sporulation and growth,sugar utilization,stress responses,and virulence of the pathogen.Our results on CreA in F.proliferatum showed that PFK1 gene expression in the △creA deletion mutant was up-regulated,while HXT3,PEPCK,and FBP1 were down-regulated when compared to the wild type.This revealed that the △crea increased rate of glycolysis,while decreased sugar transport and gluconeogenesis efficiencies.The △crea mutant also showed impaired growth on sugars,indicating that creA has a special role in sugar utilization in F.proliferatum.In addition,compared with the wild type,the virulence,the content of fumonisin and the expression levels of fumonisin synthesis genes FUM1,FUM6 and FUM8 of ΔcreA decreased,indicating that creA may regulate the pathogenicity and biosynthesis of Fusarium in F.proliferatum.