Effect Of Temperature On Growth And Metabolism In Aspergillus Flavus

Aflatoxin is a secondary metabolite in the seeds of a number of crops with strong carcinogenic,teratogenic and mutagenic effects,and has brought greatly economic losses to the food industry.As human pathogens,Aspergilltus species can damage human hearlth.Recent progress shows that aflatoxin biosynthesis is strongly dependent on a variety of environmental factors,and one of the predominant is temperature.However,little knowledge is available about the mechanism underlying the temperature dependent regulation of aflatoxin production in Aspergillus flavus.In order to investigate effect of temperature on growth and metabolism in Aspergillus flavus,we cultured the standard strains NRRL3357 under four different temperatures firstly.The results showed that aflatoxin was produced optimally at 28?,and production decreases as temperature approach 37?,the optimum temperature for fungal growth.Under lower temperature(20?),the growth and aflatoxin production was inhibited.Conversely,when the temperature was raised to 42 ?,aflatoxin production was completely inhibited.Additionally,the number of spores was higher at 37?compared to 28?.The length of hypha tip was shorter but the distance between adjacent septa was longer at 37?.Transcriptional analysis of Aspergillus flavus cultured in different temperature showed that there were 2285 genes upregulated in the condition of 37? compared to 28?,and 3202 genes down-regulated.We obtained the proteome data by iTRAQ,and there were 337 proteins upregulated in 37?,while 328 proteins down-regulated.When the correlation was analyzed between transcriptome and proteome,it showed that they were poor correlated,indicating that the transcripts and the proteins did not correlate exactly.For example,the translation level of AflR in aflatoxin biosynthesis pathway did not change under different temperature,while its transcript level significantly increased at 37?compared to 28?.Finally,we constructed a ?Spml mutant to examine the function of this gene,related to transduce external stimuli into cellular responses in yeast.And we founded that growth of mutant was inhibited and the toxin production increased significantly compared to wild type.Moreover,the mutant was more sensitive to the cell wall stabilizer,osmotic stress,and reagents affecting cell wall integrity.In addition,the response of mutant to the oxidizing agent was parallel to that of wild type.In summary,this study is to provide evidence that temperature could affect the growth of Aspergillus flavus,and we had found many genes related to growth and aflatoxin production through the analysis of transcriptome and proteome.What is more,cell wall integrity pathway was important for growth and aflatoxin production in Aspergillus flavus.Therefore,this study made a foundation for revealing the toxin-producing mechanism in response to temperature in Aspergillus flavus.