| Peanut is one of the important economic oil crops and agricultural products for export earning in China.However,peanut is easily infected by Aspergillus flavus,sequently produce aflatoxin,which seriously threatens human,animal health and causes great economic losses.In this research,11sampling sites were selected and samples were collected in peanut producing areas.The distribution,aflatoxigenicity and infection ability of Aspergillus flavus in soils and peanuts were studied,The transcriptome differences of different infected and toxigenic strains were analyzed.,therefore,it provides theoretical basis to further study the molecular mechanism of different toxigenic Aspergillus flavus,early warning and accurate controling peanut aflatoxin contamination,thus to promote the healthy development of peanut industry in China.1.A total of 1151 Aspergillus flavus strains were isolated and identified from typical peanut producing areas in China,and the distribution characteristics of A.flavus in soils and peanuts were studied.1262 soils and peanuts was collected from 11 sampling sites in major peanut producing areas in China,1151 of A.flavus strains and 2 of A.parasiticus strains were screened through separating,purificating and ITS sequence identification.The results showed the colony number of Aspergillus flavus in soil and peanut were 158.2 and 40.1 CFU/g,respectively.The results of distribution with A.flavus in different peanut growing sites,periods,soil types and geographical locations were as follows:（1）A.flavus was widely found in Pengan of Sichuan province（181.0 CFU/g）and Zhangshu of Jiangxi province（135.8 CFU/g）in Yangtze river basin,less distributed in Fuxin of Liaoning province（31.9 CFU/g）in northeast region and Jiyang of Shandong province（6.7 CFU/g）in north region.（2）The colony number of A.flavus in soil and peanut samples during harvest（112.2 CFU/g）was significantly higher than that in 30 days before harvest（66.1 CFU/g）.（3）The colony number of A.flavus in sandy soil,loam soil,clay was 28.1,95.5 and 175.1 CFU/g,respectively.Therefore,the colony number of A.flavus showed difference in different types of soil:clay>loam soil>sandy soil.（4）The distribution of A.flavus within the scope of longitude 97°0′-125°0′（E）,latitude21°0′-47°0′（N）,altitude 4-1630 m was studied.The results showed the colony number of A.flavus in soil above 200.0 CFU/g was mainly distributed in 106°18′-117°67′（E）,21°15′-32°53′（N）or latitude19.8-115 m.2.The toxigenicity and infection ability of A.flavus were determined in typical peanut producing areas in China.（1）A total of 222 Aspergillus flavus strains,the atoxigenic and toxigenic strains were accounted for 14.9%and 85.1%,respectively.The toxigenic strains mainly produced B group toxins,especially AFB1.There were 4 types of toxigenic strains and the strains producing B1 and B2 toxin were the most,accounting for 53.2%.The average aflatoxin content of A.flavus in Taixing of Jiangsu province in the Yangtze river basin was the highest（11124.8μg/L）and the lower found in Fuxin of Liaoning province in northeast（2756.6μg/L）.（2）The characteristics of toxigenicity of A.flavus in the scope of longitude 97°0′-125°0′（E）,latitude 21°0′-47°0′（N）,altitude 4-1630 m were analyzed,found AFB1 production of A.flavus strains above 10000μg/L were distributed more in 110°0′-121°42′（E）,31°0′-37°0′（N）or altitude 4-213m.（3）The research about different toxigenic strains infecting peanut was carried out,the result showed there was no significant correlation between the infection ability of A.flavus and its toxigenicity,but the two differential strains was screening out.The infection index of HBHA-1-4（low toxigenic）to Zhonghua 6 and Yueyou 256 was lower（0.21,0.31）,HBHA-8-17（high toxigenic）was higer（0.77,0.85）.3.The difference of expression profile about different toxigenic A.flavus strains were preliminarily studied,The expression of differentially expressed genes related to aflatoxin production by A.flavus was determined.In order to further study the molecular mechanism of different toxigenic A.flavus strains,the expression profiles of low and high toxigenic A.flavus strains at two treatment time points were studied by transcriptome sequencing（cultured for 3 or 5 days）,and the results were verified by qRT-PCR.The results are as follows:（1）With the extension of culture time,the differentially gene expression patterns of low and high toxigenic strains exist significant difference:1)Compared to culture for 3 days,the number of significantly differentially expressed genes of low toxigenic strain is highest（2356）after 5 days.Moreover,the up-regulated genes was much more（1198）,and the number of differentially expressed genes from high toxigenic strain was less（1910）,were mainly for the down-regulated genes（1462）.2)With the extension of incubation time,and genes related to aflatoxin synthesis of the high toxigenic strain（after 5 days）were mainly down-regulated.With the extension of incubation time,the gene（AFLA010550）encodes sterigmatocystin 8-O-methyltransferase,aflK,aflQ,aflP,aflO,aflL,aflE,aflJ,aflC which related to aflatoxin production were all down-regulated,show that aflatoxin precursor synthesis in high toxigenic strain was inhibited（2）After cultured for 3 or 5 days,the low and high toxigenic strains were significantly different on transcription levels:1)After 3 days,compared to low toxigenic strain,the up-regulated genes（1481）were much more than the down-regulated genes（441）in high toxigenic strain.After 5 days,the up-regulated genes were reduced（864）and the down-regulated genes were increased（750）.2)At the same culture time,compared to low toxigenic strain,the genes related to the aflatoxin synthesis in the high toxigenic strain were mainly up-regulated.3)Compared to low toxigenic strain,the expression of 7differential gene（aflK、aflQ、aflP、aflO、aflM、aflE、aflJ）in aflatoxin metabolism gene cluster were significantly up-regulated in high toxigenic strain,promoted the production of aflatoxin precursor substances,might result in significant toxigenic difference between low and high toxigenic strains. |
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