Secondary Metabolism and Development Is Mediated by LlmF Control of VeA Subcellular Localization in Aspergillus nidulans

Abstract

Secondary metabolism and development are linked in Aspergillus through the conserved regulatory velvet complex composed of VeA, VelB, and LaeA. The founding member of the velvet complex, VeA, shuttles between the cytoplasm and nucleus in response to alterations in light. Here we describe a new interaction partner of VeA identified through a reverse genetics screen looking for LaeA-like methyltransferases in Aspergillus nidulans. One of the putative LaeA-like methyltransferases identified, LlmF, is a negative regulator of sterigmatocystin production and sexual development. LlmF interacts directly with VeA and the repressive function of LlmF is mediated by influencing the localization of VeA, as over-expression of llmF decreases the nuclear to cytoplasmic ratio of VeA while deletion of llmF results in an increased nuclear accumulation of VeA. We show that the methyltransferase domain of LlmF is required for function; however, LlmF does not directly methylate VeA in vitro. This study identifies a new interaction partner for VeA and highlights the importance of cellular compartmentalization of VeA for regulation of development and secondary metabolism.

A Novel Automethylation Reaction in the Aspergillus nidulans LaeA Protein Generates S-Methylmethionine

“…Such a function has been supported by the loss of LaeA function in vivo in a double mutation in motif I (23). Furthermore, it has been shown that LaeA can bind AdoMet in vitro (31). These data all suggest that LaeA could be a bona fide methyltransferase.…”

“…Strains harboring a single integration of the complementation vector at the pyroA locus were subsequently crossed to RJW130.1 (pyroA4 and ⌬laeA) and/or RJMP260.28 (pyroA4, hhoA-mCherry, and ⌬laeA) to generate prototrophic strains. Analysis of sterigmatocystin production was done from point-inoculated cultures grown for 4 days in dark and light conditions, and sterigmatocystin was extracted and visualized via thin layer chromatography (31). Analysis of asexual and sexual sporulation was conducted as described previously (34) with the minor modification of using Champe's media for sexual developmental induction (35).…”

“…Analysis of asexual and sexual sporulation was conducted as described previously (34) with the minor modification of using Champe's media for sexual developmental induction (35). Visualizing the cellular localization of LaeA-GFP fusion proteins was conducted as described previously in Palmer et al (31) using a Zeiss AxioVision A10 microscope. Protein Extraction from Aspergillus-Extracts were prepared from cells in vegetative, asexual, and sexual growth stages.…”

Fungal Morphogenesis, from the Polarized Growth of Hyphae to Complex Reproduction and Infection Structures

“…The absence of LaeA results directly or indirectly in increased repressive trimethylation marks at histone 3 in A. nidulans (372) or Trichoderma atroviride (373). VeA is a hub for several interacting methyltransferases, including LaeA, VipC/LlmB, VapB, or LlmF in A. nidulans or P. chrysogenum (374)(375)(376). The A. nidulans VipC-VapB methyltransferase heterodimer acts as negative regulator of sexual development and as a positive regulator of asexual development and is part of an epigenetic methyltransferase signal transduction pathway.…”

Key Players in the Regulation of Fungal Secondary Metabolism

“…Once assembled in the nucleus of A. nidulans, the velvet complex drives sexual development and production of SMs, whereas these processes are repressed under illuminating conditions resulting from a dissociated velvet complex [81]. Consequently, when localization of members of this complex is compromised, such as with VeA via interacting with the newly described LaeA-like methyltransferase LlmF, neither sexual development nor SM production can proceed normally [98]. The LlmF mechanism of VeA control appears conserved in other ascomycetes as well [99].…”