RESEARCH ARTICLE Fusarium verticillioides chitin synthases CHS5 and CHS7 are required for normal growth and pathogenicity Troy M. Larson • David F. Kendra • Mark Busman • Daren W. Brown Received: 29 September 2010 / Revised: 21 December 2010 / Accepted: 3 January 2011 / Published online: 19 January 2011 Ó Springer-Verlag (outside the USA) 2011 Abstract Fusarium verticillioides is both an endophyte and a pathogen of maize and is a health threat in many areas of the world because it can contaminate maize with fumonisins, a toxic secondary metabolite. We identified eight putative chitin synthase (CHS) genes in F. verticil- lioides genomic sequence, and phylogenetic evidence shows that they group into seven established CHS gene classes. We targeted two CHSs (CHS5 and CHS7) for deletion analysis and found that both are required for normal hyphal growth and maximal disease of maize seedlings and ears. CHS5 and CHS7 encode a putative class V and class VII fungal chitin synthase, respectively; they are located adjacent to each other and are divergently transcribed. Fluorescent microscopy found that both CHS deficient strains produce balloon-shaped hyphae, while growth assays indicated that they were more sensitive to cell wall stressing compounds (e.g., the antifungal com- pound Nikkomycin Z) than wild type. Pathogenicity assays on maize seedlings and ears indicated that both strains were significantly reduced in their ability to cause disease. Our results demonstrate that both CHS5 and CHS7 are neces- sary for proper hyphal growth and pathogenicity of F. verticillioides on maize. Keywords Chitin synthase Á CHS Á Fusarium spp. Á Cell wall Á Endophyte Á Fumonisin Introduction Fusarium verticillioides (teleomorph Gibberella monili- formis) is an endophyte of maize as well as a pathogen capable of causing seedling diseases, and ear and stalk rots. Although the physical damage to some maize may be significant, the overriding health and economic concern centers on the ability of the fungus to produce fumonisins, which may contaminate maize and maize products (Bacon et al. 2008; Munkvold and Desjardins 1997). The fungus is capable of producing several mycotoxins, including fumonisins, which are associated with liver and kidney cancers and neural tube defects (Bacon et al. 2008; Howard et al. 2001; Seefelder et al. 2003). As an endophyte, F. verticillioides can colonize maize during all stages of the plant’s life cycle and provide pro- tection from other, more virulent fungal pathogens (Wicklow et al. 1988; Yates et al. 1997). Although non- specialized hyphae are involved in nutrient absorption during endophytic growth, nothing is known about cell wall biosynthesis and morphogenesis during this phase (Bacon and Hinton 1996). Conversion from an endophyte to a pathogen is influenced by both abiotic and biotic factors, as well as morphological and genetic attributes of the maize plant. High contamination levels of fumonisins and other fungal toxins are often associated with the most diseased seeds. To develop strategies that limit fumonisin Communicated by B. Cormack. Names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by USDA implies no approval of the product to the exclusion of others that may also be suitable. Electronic supplementary material The online version of this article (doi:10.1007/s00294-011-0334-6) contains supplementary material, which is available to authorized users. T. M. Larson (&) Á D. F. Kendra Á M. Busman Á D. W. Brown Bacterial Foodborne Pathogens and Mycology Research Unit, Agricultural Research Service, U.S. Department of Agriculture, 1815 North University Street, Peoria, IL 61604-3999, USA e-mail: troy.larson@ars.usda.gov 123 Curr Genet (2011) 57:177–189 DOI 10.1007/s00294-011-0334-6 10236