Affiliation:
1. Department of Biology, Texas A&M University, College Station, Texas, USA
Abstract
ABSTRACT
Aspergillus fumigatus
produces heavily melanized infectious conidia. The conidial melanin is associated with fungal virulence and resistance to various environmental stresses. This 1,8-dihydroxynaphthalene (DHN) melanin is synthesized by enzymes encoded in a gene cluster in
A. fumigatus
, including two laccases, Abr1 and Abr2. Although this gene cluster is not conserved in all aspergilli, laccases are critical for melanization in all species examined. Here we show that the expression of
A. fumigatus
laccases Abr1/2 is upregulated upon hyphal competency and drastically increased during conidiation. The Abr1 protein is localized at the surface of stalks and conidiophores, but not in young hyphae, consistent with the gene expression pattern and its predicted role. The induction of Abr1/2 upon hyphal competency is controlled by BrlA, the master regulator of conidiophore development, and is responsive to the copper level in the medium. We identified a developmentally regulated putative copper transporter, CtpA, and found that CtpA is critical for conidial melanization under copper-limiting conditions. Accordingly, disruption of CtpA enhanced the induction of
abr1
and
abr2
, a response similar to that induced by copper starvation. Furthermore, nonpigmented
ctpA
Δ conidia elicited much stronger immune responses from the infected invertebrate host
Galleria mellonella
than the pigmented
ctpA
Δ or wild-type conidia. Such enhancement in eliciting
Galleria
immune responses was independent of the
ctpA
Δ conidial viability, as previously observed for the DHN melanin mutants. Taken together, our findings indicate that both copper homeostasis and developmental regulators control melanin biosynthesis, which affects conidial surface properties that shape the interaction between this pathogen and its host.
Publisher
American Society for Microbiology
Subject
Molecular Biology,General Medicine,Microbiology
Cited by
59 articles.
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