Oxylipins called psi factors have been shown to alter the ratio of asexual to sexual sporulation in the filamentous fungus Aspergillus nidulans. Analysis of the A. nidulans genome has led to the identification of three fatty acid oxygenases (PpoA, PpoB and PpoC) predicted to produce psi factors. Here, it is reported that deletion of ppoB (DppoB) reduced production of the oleic-acid-derived oxylipin psiBb and increased the ratio of asexual to sexual spore development. Generation of the triple mutant DppoADppoBDppoC resulted in a strain deficient in producing oleic-and linoleic-acid-derived 89-hydroxy psi factor and caused increased and mis-scheduled activation of sexual development. Changes in asexual to sexual spore development were positively correlated to alterations in the expression of brlA and veA, respectively. PpoB and/or its products antagonistically mediate the expression levels of ppoA and ppoC, thus revealing regulatory feedback loops among these three genes. Phylogenetic analyses showed that ppo genes are present in both saprophytic and pathogenic Ascomycetes and Basidiomycetes, suggesting a conserved role for Ppo enzymes in the life cycle of fungi.

The ability of fungi to produce both meiospores and mitospores has provided adaptive advantages in survival and dispersal of these organisms. Here we provide evidence of an endogenous mechanism that balances meiospore and mitospore production in the model filamentous fungus Aspergillus nidulans. We have discovered a putative dioxygenase, PpoC, that functions in association with a previously characterized dioxygenase, PpoA, to integrate fatty acid derived oxylipin and spore production. In contrast to PpoA, deletion of ppoC significantly increased meiospore production and decreased mitospore development. Examination of the PpoA and PpoC mutants indicate that this ratio control is associated with two apparent feedback loops. The first loop shows ppoC and ppoA expression is dependent upon, and regulates the expression of, nsdD and brlA, genes encoding transcription factors required for meiospore or mitospore production, respectively. The second loop suggests Ppo oxylipin products antagonistically signal the generation of Ppo substrates. These data support a case for a fungal "oxylipin signature-profile" indicative of relative sexual and asexual spore differentiation.

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