LaeA Control of Velvet Family Regulatory Proteins for Light-Dependent Development and Fungal Cell-Type Specificity

Abstract

VeA is the founding member of the velvet superfamily of fungal regulatory proteins. This protein is involved in light response and coordinates sexual reproduction and secondary metabolism in Aspergillus nidulans. In the dark, VeA bridges VelB and LaeA to form the VelB-VeA-LaeA (velvet) complex. The VeA-like protein VelB is another developmental regulator, and LaeA has been known as global regulator of secondary metabolism. In this study, we show that VelB forms a second light-regulated developmental complex together with VosA, another member of the velvet family, which represses asexual development. LaeA plays a key role, not only in secondary metabolism, but also in directing formation of the VelB-VosA and VelB-VeA-LaeA complexes. LaeA controls VeA modification and protein levels and possesses additional developmental functions. The laeA null mutant results in constitutive sexual differentiation, indicating that LaeA plays a pivotal role in inhibiting sexual development in response to light. Moreover, the absence of LaeA results in the formation of significantly smaller fruiting bodies. This is due to the lack of a specific globose cell type (Hülle cells), which nurse the young fruiting body during development. This suggests that LaeA controls Hülle cells. In summary, LaeA plays a dynamic role in fungal morphological and chemical development, and it controls expression, interactions, and modification of the velvet regulators.

Fungal S-adenosylmethionine synthetase and the control of development and secondary metabolism in Aspergillus nidulans

“…SasA is not restrictively localized during asexual development to a distinct cell type but is visible in the cytoplasm of entire conidiophores including the conidiospores. During sexual development, SasA is localized to the ascospores but not to the Hülle cells, which are the nursing cells surrounding the cleistothecium (Sarikaya Bayram et al, 2010).…”

“…During illumination, primarily green asexual spores (conidia) are formed on conidiophores, whereas the sexual structures are repressed by light and primarily formed in dark and under limited oxygen levels (Adams et al, 1998;Bayram et al, 2010;Braus et al, 2010Braus et al, , 2002Purschwitz et al, 2008). The closed sexual fruiting bodies (cleistothecia) are surrounded by nursing Hülle cells (Sarikaya Bayram et al, 2010) and contain the red ascospores. Light is sensed by photoreceptors that transmit the signal to recipients like the velvet regulators.…”

“…A. nidulans LaeA is required for secondary metabolite expression of the sterigmatocystin (ST) or penicillin clusters (Bok and Keller, 2004;Bok et al, 2006). An additional role of LaeA is its requirement for Hülle cell formation (Sarikaya Bayram et al, 2010). LaeA carries a conserved SAM-binding site typical for nuclear protein methyltransferases (Bok and Keller, 2004;Kozbial and Mushegian, 2005) and there is accumulating evidence for an epigenetic control function of LaeA by chromatin remodeling (Reyes-Dominguez et al, 2010).…”

Role of the Alternaria alternata Blue-Light Receptor LreA (White-Collar 1) in Spore Formation and Secondary Metabolism

“…The function of this protein is not well analyzed in A. nidulans, and it is not yet clear whether light perception via this protein is possible at all (our unpublished studies). In addition to the light receptors, we found a 604-aa homologue to the VeA protein which coordinates light signaling with fungal development and secondary metabolism in A. nidulans by taking part in a complex with the light receptors FphA, LreA, and LreB as well as in the velvet complex with VeB and LaeA (24)(25)(26)(27). It contains a potential PEST domain like that in A. nidulans VeA, but a nuclear localization signal (NLS) or nuclear export signal (NES) was not found.…”

Quantitative proteomics reveals the mechanism and consequence of gliotoxin-mediated dysregulation of the methionine cycle in Aspergillus niger

“…In A. nidulans, VeA and LaeA form a trimeric complex with another member of the velvet protein family, VelB, and this complex is responsible for the regulation of secondary metabolism and development [56]. Apart from functionality in secondary metabolism, LaeA in A. nidulans also controls expression of carbohydrate metabolism enzymes such as Hülle cell specific α-mutanase, which is involved in establishment of fully mature fruiting bodies [57]. In Trichoderma reesei, LAE1 (A. nidulans LaeA ortholog) has been shown to regulate the expression of genes involved in lignocellulose degradation whereby in a lae1 deletion mutant, a number of cellulases and xylanases were no longer expressed.…”