A cyclin-dependent kinase family member (PHOA) is required to link developmental fate to environmental conditions in Aspergillus nidulans

We addressed the question of whether Aspergillus nidulans has more than one cyclin-dependent kinase gene and identified such a gene, phoA, encoding two PSTAIRE-containing kinases (PHOA(M1) and PHOA(M47)) that probably result from alternative pre-mRNA splicing. PHOA(M47) is 66% identical to Saccharomyces cerevisiae Pho85, The function of this gene was studied using phoA null mutants. It functions in a developmental response to phosphorus-limited growth but has no effect on the regulation of enzymes involved in phosphorus acquisition. Aspergillus nidulans shows both asexual and sexual reproduction involving temporal elaboration of different specific cell types. We demonstrate that developmental decisions in confluent cultures depend upon both the initial phosphorus concentration and the inoculation density and that these factors influence development through phoA. In the most impressive cases, absence of phoA resulted in a switch from asexual to sexual development (at pH 8), or the absence of development altogether (at pH 6), The phenotype of phoA deletion strains appears to be specific for phosphorus limitation. We propose that PHOA functions to help integrate environmental signals with developmental decisions to allow ordered differentiation of specific cell types in A. nidulans under varying growth conditions. The results implicate a putative cyclin-dependent kinase in the control of development.