AoOTAbZIP mediates osmotic pressure regulation of growth and toxin production by Aspergillus ochraceus fc-1

MA Yanling; LI Mingxuan; DENG Yingyao; ZHUANG Muyuan; LIU Yang

Abstract：Ochratoxin is a mycotoxin of worldwide concern,of which Ochratoxin A(OTA)is a low molecular weight,highly toxic and secondary metabolite produced by different Aspergillus and Penicillium species.In order to investigate the functional role of bZIP gene under NaCl-induced osmotic stress,a Δ bZIP mutant was constructed to investigate the role of AoOTAbZIP gene in Aspergillus ochraceus in mediating the regulation of OTA synthesis by osmotic stress,with the aim of comparing the fungal growth and OTA production of the wild-type and the mutant strains under different osmotic stress conditions.In a moderate osmotic stress(20 g/L NaCl)medium,growth of the wild-type and mutant strains was promoted(20％growth of the wild-type and 20％growth of the mutant)compared to the control(0 g/L NaCl),and the amount of virulence produced by the wild-type was increased 7-fold,while no virulence production was detected in the mutant strain.In a medium with high osmotic stress(100 g/L NaCl),there was a significant inhibitory effect on the growth of the wild-type and mutant strain(65％reduction in the wild-type and 60％reduction in the mutant strain),a reduction in the production of poison in the wild-type(about 34％reduction),and no production of poison by the mutant strain was detected,as compared to the control(0 g/L NaCl);These results indicated that the deletion of bZIP gene enhanced the mutant strain's tolerance to osmotic stress and eliminated OTA production.The expression of the OTA synthesis genes otaA,otaB,otaC,and otaD was extremely low in the ΔAoOTAbZIP strain compared to the wild type,suggesting that the AoOTAbZIP genes are involved in the synthesis of OTA through the regulation of OTA synthesis gene expression.In pathogenicity experiments,no significant difference was found between the wild-type and ΔAoOTAbZIP mutant strains on grapevine,suggesting that deletion of the AoOTAbZIP gene has no significant effect on the pathogenicity of A.ochraceus.