Light regulation of secondary metabolism in fungi

Abstract

Fungi have evolved unique metabolic regulation mechanisms for adapting to the changing environments. One of the key features of fungal adaptation is the production of secondary metabolites (SMs), which are essential for survival and beneficial to the organism. Many of these SMs are produced in response to the environmental cues, such as light. In all fungal species studied, the Velvet complex transcription factor VeA is a central player of the light regulatory network. In addition to growth and development, the intensity and wavelength of light affects the formation of a broad range of secondary metabolites. Recent studies, mainly on species of the genus Aspergillus, revealed that the dimer of VeA-VelB and LaeA does not only regulate gene expression in response to light, but can also be involved in regulating production of SMs. Furthermore, the complexes have a wide regulatory effect on different types of secondary metabolites. In this review, we discussed the role of light in the regulation of fungal secondary metabolism. In addition, we reviewed the photoreceptors, transcription factors, and signaling pathways that are involved in light-dependent regulation of secondary metabolism. The effects of transcription factors on the production of secondary metabolites, as well as the potential applications of light regulation for the production of pharmaceuticals and other products were discussed. Finally, we provided an overview of the current research in this field and suggested potential areas for future research.

Keywords: LaeA; Light regulation; Secondary metabolites; VeA.

Fig. 1

Model of the light regulation of secondary metabolism in Aspergillus nidulans. The subcellular localization of VeA in fungi is regulated by various factors. A cytoplasmic VeA-VelB dimer is recognized by importin alpha (KapA) and imported through the nuclear pore complex. Once inside the nucleus, a heterotrimeric complex consisting of LaeA, VeA, and VelB activates secondary metabolism. A transient complex between LlmF and VeA plays a role in repressing the nuclear import of VeA, primarily through the putative methylation activity of LlmF [60]. Furthermore, the red light-sensing phytochrome, FphA, also influences the subcellular localization of VeA. However, it remains unknown whether FphA and LlmF share a common pathway or independently regulate VeA’s subcellular localization