Functional diversification of sterol regulatory element binding proteins following gene duplication in a fungal species

The sterol regulatory element binding proteins (SREBPs) are functionally well conserved and have been shown to regulate ergosterol synthesis in fungi. However, the distribution and evolution of the SREBPs in fungi, especially in the Pezizomycotina which comprised of a great many of animal and plant pathogens, are unexplored. In this study, we identified 641 SREBPs from 367 out of 530 fungi species. Reconstruction of their evolutionary history showed evidence of gene duplication and gene loss at multiple evolutionary scales. Especially, SREBPs undergo a gene duplication event in the common ancestor of Pezizomycotina, resulting in the formation of two clades of SREBPs. Besides, the conserved motifs in the bHLH domain of both clades within Eurotiomycetes are highly diverged. To better understand the evolutionary diversification of this biologically significant regulator, we performed a series of experiments using Penicillium digitatum, a member of the lineage of Eurotiomycetes, to investigate how the evolutionary process of gene duplication shaped its function. qRT-PCR analysis showed that although PdsreA and PdsreB can be induced by imazalil, they showed different expression pattern; the electrophoretic mobility shift assay showed that PdSreA but not PdSreB can directly bind to the PdMLE1 sequence, an element that leads to the increased resistance to demethylation inhibitors (DMI) fungicides in P. digitatum. These results demonstrated that functions of duplicated SREBPs have largely diverged in P. digitatum, which may be a major feature of the long-term adaptive evolution of a particular group of fungi.