Environmental factors, such as nutrients, light, and pheromones, can induce fungi, such as Aspergillus nidulans, to switch from vegetative growth to reproduction. Aspergillus can reproduce asexually by forming structures called conidia or sexually by forming fruiting bodies. Light favors asexual reproduction, and darkness favors sexual reproduction. The nuclear VelB-VeA-LaeA complex activates genes required for sexual development and secondary metabolism. VelB and VeA together mediate DNA binding, and LaeA is a methyltransferase. Environmental chemical cues control the formation of VelB-VeA heteromers, and light reduces the nuclear import of VeA, so VelB-VeA-LaeA accumulates in the nucleus only when conditions are favorable for sexual reproduction. Using biochemical and genetic techniques, Sarikaya-Bayram et al. delineated a signaling pathway that reduced the nuclear accumulation of VeA and stimulated asexual development. The methyltransferases VipC and VapB formed complexes with the plasma membrane–associated protein VapA, and VipC-VapB heteromers were also present in the nucleus. Whereas plasma membrane–associated VapA-VipC-VapB promoted sexual development, nuclear VipC-VapB reduced sexual development and stimulated the expression of genes required for asexual development. Both VipC and VapB directly interacted with VeA, and release of VipC-VapB from the plasma membrane reduced the expression of veA and nuclear accumulation of VeA, possibly by decreasing VeA nuclear import or by promoting its degradation. The environmental cues that trigger the release of VipC-VapB from VapA have not been identified. These results identify a mechanism whereby controlled localization of methyltransferases influences whether Aspergillus reproduces sexually or asexually and coordinates the developmental program with secondary metabolism.
Ö. Sarikaya-Bayram, Ö. Bayram, K. Feussner, J.-H. Kim, H.-S. Kim, A. Kaever, I. Feussner, K.-S. Chae, D.-M. Han, K.-H. Han, G. H. Braus, Membrane-bound methyltransferase complex VapA-VipC-VapB guides epigenetic control of fungal development. Dev. Cell, 29, 406–420 (2014). [PubMed]