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

Gang Wang,Li Li,Yulong Wang,Erfeng Li,Junning Ma,Fei Liu,Chenxi Zhang,Bolei Yang,Yang Liu,Haiyong Zhang

doi:10.3389/fmicb.2019.02759

Abstract

Aspergillus ochraceus 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 A. ochraceus. The loss of laeA, veA, and velB 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 laeA, veA, and velB drastically reduced the production of OTA. The wild-type A. ochraceus 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 A. ochraceus.

Highlights

Ochratoxin A (OTA) is the secondary metabolite of Aspergillus and Penicillium species (Wang et al, 2016a,b)
We have identified and deleted the members of velvet complex in A. ochraceus and explored their regulatory role in growth morphology, ochratoxin A (OTA) biosynthesis and fungal virulence on pears
A phylogenetic tree of evolutionary relationship of LaeA proteins from various species including OTA producing fungi was constructed (Figure 1), revealing that LaeA was conserved among the Aspergillus species

Summary

Introduction

Ochratoxin A (OTA) is the secondary metabolite of Aspergillus and Penicillium species (Wang et al, 2016a,b). That poses a serious health hazard according to its mycotoxic properties (Taniwaki et al, 2018). It is classified as a possible human carcinogen (group 2B) by the International Agency for Research on Cancer (IARC, 1993). OTA was first isolated from A. ochraceus in 1965 (van der Merwe et al, 1965). It was reported to be the major contributor of OTA in cereal, Zea mays, coffee, fruits, and beverage (Mantle, 2002).

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