A farnesoic acid‐responsive transcription factor, Hot1, regulates yeast‐hypha morphogenesis in Candida albicans

Abstract

Candida albicans hyphal formation is inhibited by a quorum-sensing molecule, farnesoic acid, which accumulates in the medium as the cells proliferate. We recently showed that Pho81 is essential for the inhibition of hyphal growth by farnesoic acid. Here, we describe a newly identified regulator, Hot1, which increases the expression of PHO81. The binding site of Hot1 in the PHO81 promoter region was identified by DNase I protection assay. The hot1Δ mutant grows extensively as filaments. Furthermore, the inhibition of hyphal formation and the repression of major signaling pathway components in response to farnesoic acid are defective in hot1Δ mutant cells. These data suggest an important role for HOT1 in the inhibition of hyphal development by farnesoic acid in this fungus.

Quorum sensing in Candida albicans: farnesol versus farnesoic acid

“…The pho81Δ mutant cells existed exclusively as filaments and were insensitive to inhibition by FA. Second, the mRNA abundance of HOT1 and PHO81 increased dramatically between 40 and 240 min following treatment with FA, but remained unchanged following treatment with FOH [6]. Similar to the pho81Δ strain from their previous work, the hot1Δ mutant cells grew exclusively as filaments and were insensitive to FA inhibition of hyphal morphogenesis.…”

“…Pho81p was identified as a cyclin-dependent kinase inhibitor, and its activation by phosphate-limiting conditions leads to a decrease in Pho80/Pho85 activity, leading to dephosphorylation and activation of Pho4. If we assume that it is the hypophosphorylated, nuclear-localized form of Pho4p that is active in the regulation of filamentation, this raises a conflict with the data presented by Chung et al [8] and Ahn et al [6]. Pho4p is a basic helix-loop-helix transcription factor that binds to and activates genes involved with phosphate acquisition and polyphosphate mobilization, and the work of Ikeh et al [12] showed that a pho4Δ mutant strain fails to form hyphal germ tubes under hyphae-inducing conditions.…”

“…A pho81Δ mutant strain would be expected to accumulate hyperphosphorylated Pho4p, which is actively excluded from the nucleus and thus inactive as a transcriptional regulator. If we assume that it is the hypophosphorylated, nuclear-localized form of Pho4p that is active in the regulation of filamentation, this raises a conflict with the data presented by Chung et al [8] and Ahn et al [6]. Specifically, a pho81Δ mutant strain would be expected to favor the inactive form of Pho4p.…”

“…This question has now been partially answered by Ahn et al [6], who explored how FA blocks mycelial development of C. albicans SC5314. Previously, the same authors had shown that CaPHO81, a key component of the phosphate starvation response signal transduction pathway [7], is required for inhibition of hyphal development by FA [8].…”

“…First, the hot1Δ mutant cells had lost their sensitivity to FA but remained sensitive to FOH. Second, the mRNA abundance of HOT1 and PHO81 increased dramatically between 40 and 240 min following treatment with FA, but remained unchanged following treatment with FOH [6]. Indeed the study of PH081 and HOT1 was driven in part by the previous finding that these genes were among those induced in C. albicans 10231 following the addition of FA [9].…”