Sm. Saporitoirwin et al., PHR1, A PH-REGULATED GENE OF CANDIDA-ALBICANS, IS REQUIRED FOR MORPHOGENESIS, Molecular and cellular biology, 15(2), 1995, pp. 601-613
Candida albicans, like many fungi, exhibits morphological plasticity,
a property which may be related to its biological capacity as an oppor
tunistic pathogen of humans. Morphogenesis and alterations in cell sha
pe require integration of many cellular functions and occur in respons
e to environmental signals, most notably PH aad temperature in the cas
e of C. albicans. In the course of our studies of differential gene ex
pression associated with dimorphism of C. albicans, we have isolated a
gene, designated PHR1, which is regulated in response to the pH of th
e culture medium. PHR1 expression was repressed at pH values below 5.5
and induced at more alkaline pH. The predicted amino acid sequence of
the PHR1 protein was 56% identical to that of the Saccharomyces cerev
isiae Ggp1/Gas1 protein, a highly glycosylated cell surface protein at
tached to the membrane via glycosylphosphatidylinositol. A homozygous
null mutant of PHR1 was constructed and found to exhibit a pH-conditio
nal morphological defect. At alkaline pH, the mutant, unlike the paren
tal type, was unable to conduct apical growth of either yeast or hypha
l growth forms. This morphological aberration was not associated with
defective cytoskeletal polarization or secretion. The results suggest
that PHR1 defines a novel function required for apical cell growth and
morphogenesis.