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 tha n one cyclin-dependent kinase gene and identified such a gene, phoA, e ncoding two PSTAIRE-containing kinases (PHOA(M1) and PHOA(M47)) that p robably result from alternative pre-mRNA splicing. PHOA(M47) is 66% id entical to Saccharomyces cerevisiae Pho85, The function of this gene w as studied using phoA null mutants. It functions in a developmental re sponse to phosphorus-limited growth but has no effect on the regulatio n of enzymes involved in phosphorus acquisition. Aspergillus nidulans shows both asexual and sexual reproduction involving temporal elaborat ion of different specific cell types. We demonstrate that developmenta l decisions in confluent cultures depend upon both the initial phospho rus concentration and the inoculation density and that these factors i nfluence development through phoA. In the most impressive cases, absen ce of phoA resulted in a switch from asexual to sexual development (at pH 8), or the absence of development altogether (at pH 6), The phenot ype of phoA deletion strains appears to be specific for phosphorus lim itation. We propose that PHOA functions to help integrate environmenta l signals with developmental decisions to allow ordered differentiatio n of specific cell types in A. nidulans under varying growth condition s. The results implicate a putative cyclin-dependent kinase in the con trol of development.