title: Alternaria alternata transcription factor CmrA controls melanization and spore development.
abstract: Melanin is a black pigment widely distributed across the kingdoms, from bacterial to human. The filamentous fungus Alternaria alternata is a typical 'black fungus', which produces melanin in its hyphal and especially its asexual spore cell walls. Its biosynthesis follows the dihydroxynaphthalene (DHN) pathway with 1,8-DHN as an intermediate. Two genes, encoding a polyketide synthase (pksA) and a 1,3,8-trihydroxynaphthalene (THN) reductase (brm2), along with a putative transcription factor, CmrA, comprise a small gene cluster. Here we show that CmrA controls the expression of pksA and brm2, but that it also controls the expression of a scytalone dehydratase encoding gene (brm1) located elsewhere in the genome. The regulatory function of CmrA was shown in a reporter assay system. Al. alternata CmrA was expressed in the filamentous fungus Aspergillus nidulans where it was able to induce the expression of a reporter construct under the control of the putative pksA promoter. This suggests direct binding of CmrA to the promoter of pksA in the heterologous system. Likewise, silencing of cmrA in Al. alternata led to white colonies due to the lack of melanin. In addition, hyphal diameter and spore morphology were changed in the mutant and the number of spores reduced. Silencing of brm2 and inhibition of melanin biosynthesis by tricyclazole largely phenocopied the effects of cmrA silencing, suggesting a novel regulatory function of melanin in morphogenetic pathways.
authors: Karlsruhe Institute of Technology (KIT) - South Campus, Dept. of Microbiology, Hertzstrasse 16, D-76187 Karlsruhe, Germany.
authors: Ramona
authors: R
authors: Fetzner
authors: Karlsruhe Institute of Technology (KIT) - South Campus, Dept. of Microbiology, Hertzstrasse 16, D-76187 Karlsruhe, Germany.
authors: Kristin
authors: K
authors: Seither
authors: Karlsruhe Institute of Technology (KIT) - South Campus, Dept. of Microbiology, Hertzstrasse 16, D-76187 Karlsruhe, Germany.
authors: Maximilian
authors: M
authors: Wenderoth
authors: Karlsruhe Institute of Technology (KIT) - South Campus, Dept. of Microbiology, Hertzstrasse 16, D-76187 Karlsruhe, Germany.
authors: Andreas
authors: A
authors: Herr
authors: Karlsruhe Institute of Technology (KIT) - South Campus, Dept. of Microbiology, Hertzstrasse 16, D-76187 Karlsruhe, Germany.
authors: Reinhard
authors: R
authors: Fischer
mesh_terms: D000528:Alternaria / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism*; D001233:Aspergillus nidulans / Q000235:genetics; D003001:Cloning, Molecular; D004271:DNA, Fungal / Q000737:chemistry / Q000235:genetics; D015966:Gene Expression Regulation, Fungal; D008543:Melanins / Q000378:metabolism*; D008969:Molecular Sequence Data; D005810:Multigene Family; D017422:Sequence Analysis, DNA; D013172:Spores, Fungal / Q000254:growth & development*; D014157:Transcription Factors / Q000378:metabolism*
chemical_list: D004271:DNA, Fungal; D008543:Melanins; D014157:Transcription Factors