title: Morphological transitions governed by density dependence and lipoxygenase activity in Aspergillus flavus.
abstract: Aspergillus flavus differentiates to produce asexual dispersing spores (conidia) or overwintering survival structures called sclerotia. Results described here show that these two processes are oppositely regulated by density-dependent mechanisms and that increasing the cell density (from 10(1) to 10(7) cells/plate) results in the lowest numbers of sclerotial and the highest numbers of conidial. Extract from spent medium of low-cell-density cultures induced a high-sclerotium-number phenotype, whereas high-cell-density extract increased conidiation. Density-dependent development is also modified by changes in lipid availability. Exogenous linoleic acid increased sclerotial production at intermediate cell densities (10(4) and 10(5) cells/plate), whereas oleic and linolenic acids inhibited sclerotium formation. Deletion of Aflox encoding a lipoxygenase (LOX) greatly diminished density-dependent development of both sclerotia and conidia, resulting in an overall increase in the number of sclerotia and a decrease in the number of conidia at high cell densities (>10(5) cells/plate). Aflox mutants showed decreased linoleic acid LOX activity. Taken together, these results suggest that there is a quorum-sensing mechanism in which a factor(s) produced in dense cultures, perhaps a LOX-derived metabolite, activates conidium formation, while a factor(s) produced in low-density cultures stimulates sclerotium formation.
authors.affiliation: Department of Medical Microbiology and Immunology and Department of Plant Pathology, UW-Madison, 1550 Linden Dr., Madison, WI 53706, USA. npk@plantpath.wisc.edu
authors.forename: S
authors.initials: S
authors.lastname: Horowitz Brown
authors.forename: R
authors.initials: R
authors.lastname: Zarnowski
authors.forename: W C
authors.initials: WC
authors.lastname: Sharpee
authors.forename: N P
authors.initials: NP
authors.lastname: Keller
mesh_terms: D000595:Amino Acid Sequence; D001231:Aspergillus flavus / Q000201:enzymology / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism*; D015169:Colony Count, Microbial; D003470:Culture Media; D004271:DNA, Fungal / Q000096:biosynthesis; D017353:Gene Deletion; D005800:Genes, Fungal; D005816:Genetic Complementation Test; D019787:Linoleic Acid / Q000378:metabolism; D008084:Lipoxygenase / Q000378:metabolism*; D008969:Molecular Sequence Data; D010802:Phylogeny; D053038:Quorum Sensing; D012331:RNA, Fungal / Q000096:biosynthesis; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013172:Spores, Fungal / Q000201:enzymology / Q000235:genetics / Q000254:growth & development / Q000378:metabolism
chemical_list: D003470:Culture Media; D004271:DNA, Fungal; D012331:RNA, Fungal; D019787:Linoleic Acid; D008084:Lipoxygenase