A Plastic Vegetative Growth Threshold Governs Reproductive Capacity in Aspergillus nidulans.

Ontogenetic phases separating growth from reproduction are a common feature of cellular life. Long recognized for flowering plants and animals, early literature suggests this life-history component may also be prevalent among multicellular fungi. We establish the basis of developmental competence-the capacity to respond to induction of asexual development-in the filamentous saprotroph Aspergillus nidulans, describing environmental influences, including genotype-by-environment interactions among precocious mutants, gene expression associated with wild type and precocious competence acquisition, and the genetics of competence timing. Environmental effects are consistent with a threshold driven by metabolic rate and organism density, with pH playing a particularly strong role in determining competence timing. Gene expression diverges significantly over the competence window, despite a lack of overt morphological change, with differentiation in key metabolic, signaling, and cell trafficking processes. We identify five genes for which mutant alleles advance competence timing, including the conserved GTPase RasB (AN5832) and ambient pH sensor PalH (AN6886). In all cases examined, inheritance of competence timing is complex and non-Mendelian, with F