Requirement of LaeA, VeA, and VelB on Asexual Development, Ochratoxin A Biosynthesis, and Fungal Virulence in Aspergillus ochraceus

Abstract

<i>Aspergillus ochraceus</i> is reported to be the major contributor of ochratoxin A (OTA), classified as one of the possible human carcinogen (group 2B) by the International Agency for Research on Cancer. The heterotrimeric velvet complex proteins, LaeA/VeA/VelB, have been most studied in fungi to clarify the relation between light-dependent morphology and secondary metabolism. To explore possible genetic targets to control OTA contamination, we have identified laeA, veA, and velB in <i>A. ochraceus</i>. The loss of <i>laeA</i>, <i>veA</i>, and <i>velB</i> yielded mutants with differences in vegetative growth and conidial production. Especially, ΔlaeA almost lost the ability to generate conidiaphore under dark condition. The deletion of <i>laeA</i>, <i>veA</i>, and <i>velB</i> drastically reduced the production of OTA. The wild-type <i>A. ochraceus</i> produced about 1 and 7 μg/cm² OTA under light and dark conditions on media, whereas the three gene deletion mutants produced less than 20 ng/cm² OTA, which was correlated with a down regulation of OTA biosynthetic genes. Pathogenicity studies of ΔlaeA, ΔveA, and ΔvelB showed their reduction in disease severity in pears. Furthermore, 66.1% of the backbone genes in secondary metabolite gene cluster were significantly regulated, among which 81.6% were downregulated. Taking together, these results revealed that velvet complex proteins played crucial roles in asexual development, secondary metabolism, and fungal virulence in <i>A. ochraceus</i>.