Ste12 and Ste12-like proteins, fungal transcription factors regulating development and pathogenicity

Abstract

Ste12 and Ste12-like proteins are transcription factors found exclusively in the fungal kingdom. In the yeast model Saccharomyces cerevisiae, where the first member was identified, Ste12p was shown to regulate mating and invasive/pseudohyphal growth. In recent literature, there have been several reports of Ste12-like factors in multiple fungal systems, yeasts or filamentous fungi, with saprophytic or parasitic life-styles. In all these models, Ste12 and Ste12-like factors are involved in the regulation of fungal development and pathogenicity. In this review, we discuss the features, the regulation, and the role of Ste12 and Ste12-like factors by highlighting the similarities and dissimilarities that occur within this group.

Fig. 1.

Regulation of Ste12p activity in S. cerevisiae. In response to pheromone, the Fus3 MAPK pathway (Ste11-Ste7-Fus3) relays a phosphorylation signal to reach the Dig1p/2p complex, leading to dissociation and Ste12p phosphorylation. Ste12p homodimerization allows the transcription of mating genes containing PRE sequences. Stimulation by the mating pheromone promotes the SUMOylation of Ste12p. In the case of prolonged pheromone treatment, Ste12p is subjected to degradation through a proteasome-mediated mechanism. Upon phosphorylation by Fus3p, Tec1p is rapidly degraded via a ubiquitin-mediated mechanism (SCF Ub. Ligase). In response to filamentation signals, a phosphorylation cascade is transduced via the Kss1 MAPK pathway (Ste11p-Ste7p-Kss1p), leading to the phosphorylation of Ste12p and the dissociation of the Dig1p/2p complex from FRE sequences. The dimerization of phosphorylated Ste12p with Tec1p allows the transcription of filamentation responsive genes. P, phosphorylation; S, SUMOylation; U, ubiquitination.

Fig. 2.

Regulation of STE12-like genes by alternative splicing. STE12-like genes from filamentous fungi display a conserved intron-exon organization at the 3′ ends of their coding sequences. This part encodes two zinc finger domains (red and green circles). In the plant pathogens C. lindemuthianum and B. cinerea, an alternative splicing event corresponding to exon skipping has been identified. This results in the production of a protein with only one new zinc finger displaying an inhibitory effect on pathogenesis when overexpressed in wild-type strains (45, 51). HD, homeodomain; Zn, zinc finger.