Transcription Factor STE12α Has Distinct Roles in Morphogenesis, Virulence, and Ecological Fitness of the Primary Pathogenic YeastCryptococcus gattii

Cryptococcus gattii is a primary pathogenic yeast, increasingly important inpublic health, but factors responsible for its host predilection andgeographical distribution remain largely unknown. We have characterizedC. gattii STE12 α to probe its role in biologyand pathogenesis because this transcription factor has been linked tovirulence in many human and plant pathogenic fungi. A full-lengthSTE12 α gene was cloned by colony hybridization andsequenced using primer walk and 3′ rapid amplification of cDNAends strategies, and aste12 αΔ gene knockoutmutant was created byURA5 insertion at the homologous site. Asemiquantitative analysis revealed delayed and poor mating inste12 αΔ mutant; this defect was not reversedby exogenous cyclic AMP.C. gattii parent and mutantstrains showed robust haploid fruiting. Among putative virulencefactors tested, the laccase transcript and enzymatic activity were downregulated in theste12 αΔ mutant, withdiminished production of melanin. However, capsule, superoxidedismutase, phospholipase, and urease were unaffected. Similarly, Ste12deficiency did not cause any auxotrophy, assimilation defects, orsensitivity to a large panel of chemicals and antifungals. Theste12 αΔ mutant was markedly attenuated invirulence in both BALB/c and A/Jcr mice models of meningoencephalitis,and it also exhibited significant in vivo growth reduction and washighly susceptible to in vitro killing by human neutrophils(polymorphonuclear leukocytes). In tests designed to simulate theC. gattii natural habitat, theste12 αΔ mutant was poorly pigmented on woodagar prepared from two tree species and showed poor survival andmultiplication in wood blocks. Thus,STE12 α playsdistinct roles inC. gattii morphogenesis, virulence,and ecologicalfitness.