Comparative genomics of aspergillus flavus s and l morphotypes yield insights into niche adaptation

Authors: OHKURA, MANA - University Of Arizona; Cotty, Peter; ORBACH, MARC - University Of Arizona

Submitted to: G3, Genes/Genomes/Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/15/2018
Publication Date: 10/25/2018
Citation: Ohkura, M., Cotty, P.J., Orbach, M.J. 2018. Comparative genomics of aspergillus flavus s and l morphotypes yield insights into niche adaptation. G3, Genes/Genomes/Genetics. 8(12):3915-3930.

Interpretive Summary: Aflatoxin is a potent carcinogen that contaminates food and feed when agriculture commodities are infected with the plant pathogen, Aspergillus flavus. Two morphologies, L and S, of A. flavus have been observed that differ in sporulation patterns and in the level of aflatoxin production. To identify genomic changes between these morphotypes the sequences of three S and three L morphotype isolates were compared. Differences in genome structure and gene content were identified between the morphotypes. Numerous differences in metabolism genes were identified. These findings indicate the genomes of the two morphotypes differ beyond developmental genes and have diverged as they adapted to their respective niches.

Technical Abstract: Aspergillus flavus, the primary causal agent for aflatoxin contamination on crops, consists of isolates with two distinct morphologies: isolates of the S morphotype produce numerous small sclerotia and lower numbers of conidia while isolates of the L morphotype produce fewer large sclerotia and abundant conidia. The morphotypes also differ in aflatoxin production with S isolates consistently producing high concentrations of aflatoxin, whereas L isolates range from atoxigenic to highly toxigenic. The production of abundant sclerotia by the S morphotype suggests adaptation for long-term survival in the soil, whereas the production of abundant conidia by the L morphotype suggests adaptation for aerial dispersal to the phyllo- sphere. To identify genomic changes that support differential niche adaption, the sequences of three S and three L morphotype isolates were compared. Differences in genome structure and gene content were identified between the morphotypes. A .530 kb inversion between the morphotypes affect a secondary metabolite gene cluster and a cutinase gene. The morphotypes also differed in proteins predicted to be involved in carbon/nitrogen metabolism, iron acquisition, antimicrobial defense, and evasion of host im- munity. The S morphotype genomes contained more intact secondary metabolite clusters indicating there is higher selection pressure to maintain secondary metabolism in the soil and that it is not limited to aflatoxin production. The L morphotype genomes were enriched in amino acid transporters, suggesting efficient nitrogen transport may be critical in the nutrient limited phyllosphere. These findings indicate the genomes of the two morphotypes differ beyond developmental genes and have diverged as they adapted to their respective niches.