Abstract
The basidiomycete fungal pathogen Cryptococcus neoformans requires the PUF protein, Pum1, for hyphal morphogenesis during sexual development. In this study we found that Pum1 was auto-repressive under growth as yeast, but that auto-repression was relieved during filamentous growth through utilization of an alternative transcription start site driven by the master filamentation regulator Znf2. In addition, Pum1 was required to stabilize the ZNF2 mRNA through an indirect mechanism suggesting that Znf2 and Pum1 each positively regulate the expression of the other to achieve the filamentous morphotype required for sexual development in Cryptococcus.
Highlights
The basidiomycete fungal pathogen Cryptococcus neoformans requires the PUF protein, Pum[1], for hyphal morphogenesis during sexual development
Leaf polarity in Arabidopsis, sexual development in the malarial parasite Plasmodium falciparum, and organelle biogenesis in Saccharomyces cerevisiae constitute some of the other diverse functions performed by PUF proteins[1,5,6]
Analogous to the known roles of PUF proteins implicated in development of diverse organisms, Pum[1] in C. neoformans is required for hyphae formation and extension during sexual development after mate recognition and cell fusion[7]
Summary
Pum[1] is auto-regulatory in C. neoformans. Pum[1] is required for sexual development in C. neoformans after mate recognition and cell fusion, at the point of post-fusion hyphal extension[7]. We observed the appearance of two smaller bands in the PGAL7ZNF2 lanes in addition to the larger band seen in the wild type control that hybridized to a probe in the PUM1 RNA binding domain coding sequence (Fig. 5a) To determine if these bands encoded alternative transcripts, we performed 5′ RACE using c-DNA from PGAL7ZNF2 and two prominent bands were observed (SupplementaryFig. S3a). The identification of a shorter mRNA that begins downstream of the 5′ UTR P3E explains how under conditions of filamentation, Pum[1] auto-repression is relieved It does not account for the appearance of two shorter transcripts in the northern blot analysis. Continued investigation into mechanisms of Pum[1] de-repression could reveal a role for environmental conditions priming yeast cells for the initiation of sexual development promoting escape, environmental dissemination and survival
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