Kale Shubha P, Cary Jeffrey W, Baker Craig, Walker Danya, Bhatnagar Deepak, Bennett Joan W
Department of Biology, Xavier University of Louisiana New Orleans, LA 70125, USA.
Mycol Res. 2003 Jul;107(Pt 7):831-40. doi: 10.1017/s0953756203007998.
Aflatoxins (AFs) are secondary metabolites produced mainly by Aspergillus parasiticus and A. flavus. To study AF regulation, previously isolated non-toxigenic A. parasiticus sec- (for secondary metabolism minus) variants were genetically analysed. In parasexual crossing, the sec- strains failed to form heterokaryons and diploids with other sec- strains. Heterokaryon test results suggested that involvement of cytoplasmic elements in the formation of sec- phenotype was unlikely. At the molecular level, the coding sequence of the sec- aflR (the only known positive regulator of AF pathway) was identical to that of their toxigenic sec+ (for secondary metabolism plus) parents. However, the sec- aflR expression was 5- to 10-fold lower compared to that in the sec+ forms. RT-PCR analysis demonstrated that the AF pathway genes were expressed in the sec- forms but in trace amounts and in their unprocessed forms. Combined, these results suggest that aflR is necessary but not sufficient for AF production and that elements involved in fungal development directly or indirectly influence its proper function.
黄曲霉毒素（AFs）是主要由寄生曲霉和黄曲霉产生的次级代谢产物。为了研究AF的调控机制，对之前分离得到的不产毒的寄生曲霉sec-（代表次级代谢缺陷型）变体进行了遗传分析。在准性杂交中，sec-菌株无法与其他sec-菌株形成异核体和二倍体。异核体测试结果表明，细胞质成分不太可能参与sec-表型的形成。在分子水平上，sec- aflR（AF途径唯一已知的正调控因子）的编码序列与其产毒的sec+（代表次级代谢正常型）亲本相同。然而，sec- aflR的表达量比sec+形式低5至10倍。RT-PCR分析表明，AF途径基因在sec-形式中表达，但表达量极少且以未加工的形式存在。综合这些结果表明，aflR对于AF的产生是必要的，但不是充分的，并且参与真菌发育的元件直接或间接影响其正常功能。
