Abstract
Aspergillus nidulans asexual sporulation (conidiation) is triggered by different environmental signals and involves the differentiation of specialized structures called conidiophores. The elimination of genes flbA-E, fluG, and tmpA results in a fluffy phenotype characterized by delayed conidiophore development and decreased expression of the conidiation essential gene brlA. While flbA-E encode regulatory proteins, fluG and tmpA encode enzymes involved in the biosynthesis of independent signals needed for normal conidiation. Here we identify afeA and tmpB as new genes encoding members the adenylate-forming enzyme superfamily, whose inactivation cause different fluffy phenotypes and decreased conidiation and brlA expression. AfeA is most similar to unknown function coumarate ligase-like (4CL-Lk) enzymes and consistent with this, a K544N active site modification eliminates AfeA function. TmpB, identified previously as a larger homolog of the oxidoreductase TmpA, contains a NRPS-type adenylation domain. A high degree of synteny in the afeA-tmpA and tmpB regions in the Aspergilli suggests that these genes are part of conserved gene clusters. afeA, tmpA, and tmpB double and triple mutant analysis as well as afeA overexpression experiments indicate that TmpA and AfeA act in the same conidiation pathway, with TmpB acting in a different pathway. Fluorescent protein tagging shows that functional versions of AfeA are localized in lipid bodies and the plasma membrane, while TmpA and TmpB are localized at the plasma membrane. We propose that AfeA participates in the biosynthesis of an acylated compound, either a p-cuomaryl type or a fatty acid compound, which might be oxidized by TmpA and/or TmpB, while TmpB adenylation domain would be involved in the activation of a hydrophobic amino acid, which in turn would be oxidized by the TmpB oxidoreductase domain. Both, AfeA-TmpA and TmpB signals are involved in self-communication and reproduction in A. nidulans.
Highlights
Cell-cell communication is a process central to environmental sensing and development
We reported that inactivation of the tmpA gene, encoding a putative membrane oxidoreductase involved in the production of a sporulation signal, results in a fluffy phenotype (SoidRaggi et al, 2006). tmpA (AN0055) and afeA (AN0054) genes were found located next to each other in an inverse orientation (Soid-Raggi et al, 2006), an arrangement that is conserved in several Aspergilli
We have shown that AfeA and TmpA are enzymes that participate in a single pathway involved in the biosynthesis of a yet unknown chemical signal that regulates cell communication, brlA expression and asexual reproduction in A. nidulans
Summary
Cell-cell communication is a process central to environmental sensing and development. Filamentous fungi use different extracellular chemical signals for self and non-self communication during their life cycle. Some signals function as auto-inhibitors of spore germination to prevent spore overcrowding, others coordinate growth through regulation of cell-cell fusion events and the establishment of a mycelial network, while others regulate asexual and sexual reproduction. In filamentous fungi development and secondary metabolism are often interrelated. That is the case in Aspergillus nidulans, where asexual and sexual development (Butnick et al, 1984), as well as secondary metabolism (Tsitsigiannis and Keller, 2006), are regulated by oxylipins, collectively called the psi factor, derived from fatty acid oxidation (Tsitsigiannis and Keller, 2007). The partial inactivation of the phosphopantetheinyl transferase CfwA/NpgA, required for activation of all polyketide synthases (PKSs) and non-ribosomal peptide synthetases (NRPSs), results in an almost complete lack of asexual reproduction (Márquez-Fernández et al, 2007)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
