Functional Analysis of All Nonribosomal Peptide Synthetases in <i>Cochliobolus heterostrophus</i> Reveals a Factor, NPS6, Involved in Virulence and Resistance to Oxidative Stress

<jats:title>ABSTRACT</jats:title> <jats:p> Nonribosomal peptides, made by nonribosomal peptide synthetases, have diverse biological activities, including roles as fungal virulence effectors. Inspection of the genome of <jats:italic>Cochliobolus heterostrophus</jats:italic> , a fungal pathogen of maize and a member of a genus noted for secondary metabolite production, revealed eight multimodular nonribosomal peptide synthase ( <jats:italic>NPS</jats:italic> ) genes and three monomodular <jats:italic>NPS</jats:italic> -like genes, one of which encodes a nonribosomal peptide synthetase/polyketide synthase hybrid enzyme presumed to be involved in synthesis of a peptide/polyketide molecule. Deletion of each <jats:italic>NPS</jats:italic> gene and phenotypic analyses showed that the product of only one of these genes, <jats:italic>NPS6</jats:italic> , is required for normal virulence on maize. NPS6 is also required for resistance to hydrogen peroxide, suggesting it may protect the fungus from oxidative stress. This and all other <jats:italic>nps</jats:italic> mutants had normal growth, mating ability, and appressoria. Real-time PCR analysis showed that expression of all <jats:italic>NPS</jats:italic> genes is low (relative to that of actin), that all (except possibly <jats:italic>NPS2</jats:italic> ) are expressed during vegetative growth, and that expression is induced by nitrogen starvation. Only <jats:italic>NPS6</jats:italic> is unfailingly conserved among euascomycete fungi, including plant and human pathogens and saprobes, suggesting the possibility that NPS6 activity provides oxidative stress protection during both saprobic and parasitic growth. </jats:p>