Coordinated and independent functions of velvet-complex genes in fungal development and virulence of the fungal cereal pathogen Cochliobolus sativus

LaeA and velvet proteins regulate fungal development and secondary metabolism through formation of multimeric complexes in many fungal species, but their functions in the cereal fungal pathogen Cochliobolus sativus are not well understood. In this study, four velvet complex genes (CsLaeA, CsVeA, CsVelB, and CsVeIC) in C. sativus were identified and characterized using knockout mutants generated for each of the genes. Both Delta CsVeA and Delta CsVelB showed significant reduction in aerial mycelia growth. Delta CsVelB also exhibited a hypermorphic conidiation phenotype with indeterminate growth of the conidial tip cells and premature germination of conidia. Delta CsLaeA, Delta CsVeA, and Delta CsVelB produced more conidia under constant dark conditions than under constant light conditions whereas no differences were observed under the two conditions for the wild type. These three mutants also showed significantly reduced conidiation under constant light conditions, but produced more small sized conidia under constant dark conditions compared to the wild type. All knockout mutants (Delta CsLaeA, Delta CsVeA, Delta CsVelB and Delta CsVelC) showed some extent of reduction in virulence on susceptible barley plants compared to the wild type strain. The results revealed the conserved and unique roles of velvet-complex proteins as regulators in mediating fungal development and secondary metabolism in C. sativus. (C) 2016 British Mycological Society. Published by Elsevier Ltd. All rights reserved.