Melanin is required for the formation of the multi-cellular conidia in the endophytic fungus Pestalotiopsis microspora

Abstract

Melanin plays an important role in regulating various biological processes in many fungi. However, its biological role in conidiation remains largely elusive. We report here that conidia production, morphogenesis, integrity, germination and their viability in Pestalotiopsis microspora require the polyketide-derived melanin. A polyketide synthase gene, pks1, was identified and demonstrated responsible for melanin biosynthesis in this fungus. A targeted deletion mutant strain Δpks1 displayed a defect in pigmentation of conidia and had an albino colonial phenotype. Interestingly, Δpks1 produced approximately 6-fold as many conidia as the wild type did, suggesting a negative modulation of melanin on conidia production in this fungus. Moreover, the conidia failed to develop into the normal five-cell morphology, rather the three main-body cells separated via constriction at the original septum position to generate three independent mutant conidia. This result suggests a novel role of melanin in the formation of the multi-cellular conidia. Germ tubes could develop from the three different types of mutant conidia and kept elongating, despite a significantly lower germination rate was observed for them. Still more, the unpigmented conidia became permeable to Calcofluor White and DAPI, suggesting the integrity of the conidia was impaired. Deliberate inhibition of melanin biosynthesis by a specific inhibitor, tricyclazole, led to a similar phenotypes. This work demonstrates a new function of fungal melanin in conidial development.

A cryptic pigment biosynthetic pathway uncovered by heterologous expression is essential for conidial development in Pestalotiopsis fici

“…S3) and LC‐MS (data not shown) but no difference in metabolites was identified. The same situation also happened in the disruptions of MrPKS1 in M. robertsii (Chen et al ., ), PKS12 and PKS13 in B. cinerea (Schumacher, ) as well as PKS1 in P. microspora (Yu et al ., ). All of these PKS are involved in the pigment formation but no identified compounds were found.…”

“…Searching the genome for pigment biosynthetic genes in P. fici genome, we found a putative PKS with considerable homology to other melanin encoding enzymes. Deletion of the PKS encoding gene PfmaE led to colorless conidia and serious fractures on conidial surfaces in P. fici which is consistent with the deletion of pks1 in P. microspora (Yu et al ., ). As different extraction methods and analyses by HPLC and LC‐MS analysis could not distinguish chemical differences between WT and the PfmaE mutant, we explored an alternative approach to address this problem.…”

“…DHN melanin is a critical virulence factor for this fungus and important for spore integrity (Jahn et al, 1997(Jahn et al, , 2000(Jahn et al, , 2002Langfelder et al, 1998). Recently, studies of Alternaria alternata and the endophytic fungus Pestalotiopsis microspora demonstrated a role for melanin in multicellular spore formation by deletion of PKSs respectively (Yu et al, 2015;Wenderoth et al, 2017). These findings led to our interest in studying which pigments and how the pigments function in species with multicellular conidia.…”

Melanin production by a yeast strain XJ5-1 of Aureobasidium melanogenum isolated from the Taklimakan desert and its role in the yeast survival in stress environments

“…The reason for this is still unknown. In fungi, many PKS genes encoding the melanin biosynthesis have been cloned and characterized Loppnau et al 2004;Eisenman and Casadevall 2012;Yu et al 2015). It has been reported that the transcriptional activators Gat1, Gln3 and AreA and the transcriptional repressors Deh1, Dal80 and AreB are involved in nitrogen repression in fungi (Rød-kaer and Faergeman 2014).…”

“…6). Melanin in the conidia of an endophytic fungus P. microspora also plays an important role in resistance to the oxidative stress of H 2 O 2 (Yu et al 2015). The melanized cells of a wild-type Sporothrix schenckii were less susceptible to killing by a chemically generated oxygen from H 2 O 2 than its non-melanized cells (Romero-Martinez et al 2000).…”