YlBMH1 encodes a 14-3-3 protein that promotes filamentous growth in the dimorphic yeast Yarrowia lipolytica.

Most pathogenic fungi have the ability to alternate between a unicellular yeast form and different filamentous forms (hyphae and pseudohyphae). This attribute is generally regarded as an important virulence factor and has also attracted attention because of its implications in the study of eukaryotic cell differentiation. To identify genes that are involved in the regulation of these events, chemical mutagenesis of the dimorphic yeast Yarrowia lipolytica was performed and morphological mutants that were unable to form hyphal cells were isolated. Screening of a Y. lipolytica genomic DNA library for genes able to complement this defect led to the isolation of YlBMH1, a gene encoding a 14-3-3 protein and whose transcription levels are increased during the yeast-to-hypha transition. Remarkably, overexpression of YlBMH1 was able to enhance pseudohyphae formation in a strain lacking functional YlRAC1 but caused no visible effects in deltamhy1 and deltabem1 cells, thus suggesting that YlBMH1 is involved in the regulation of both hyphal and pseudohyphal growth in Y. lipolytica. The identification of YlBMH2, a gene encoding a second 14-3-3 protein (YlBmh2p) that contains a 19 aa insertion absent in all other members of the 14-3-3 family, is also reported. Differently from YlBMH1, the transcription levels of YlBMH2 do not show any apparent variation during the induction of hyphal growth, and its overexpression has no effects on cells lacking functional MHY1, YlRAC1 or YlBEM1. Taken together, these observations suggest that, in spite of their high conservation, YlBmh1p and YlBmh2p have different cellular functions.