A PKS gene, pks-1, is involved in chaetoglobosin biosynthesis, pigmentation and sporulation in Chaetomium globosum

Abstract

Chaetomium globosum is one of the most common fungi in nature. It is best known for producing chaetoglobosins; however, the molecular basis of chaetoglobosin biosynthesis is poorly understood in this fungus. In this study, we utilized RNA interference (RNAi) to characterize a polyketide synthase gene, pks-1, in C. globosum that is involved in the production of chaetoglobosin A. When pks-1 was knocked down by RNAi, the production of chaetoglobosin A dramatically decreased. Knock-down mutants also displayed a pigment-deficient phenotype. These results suggest that the two polyketides, melanin and chaetoglobosin, are likely to share common biosynthetic steps. Most importantly, we found that pks-1 also plays a critical role in sporulation. The silenced mutants of pks-1 lost the ability to produce spores. We propose that polyketides may modulate cellular development via an unidentified action. We also suggest that C. globosum pks-1 is unique because of its triple role in melanin formation, chaetoglobosin biosynthesis and sporulation. This work may shed light on chaetoglobosin biosynthesis and indicates a relationship between secondary metabolism and fungal morphogenesis.

QTL mapping of fungicide sensitivity reveals novel genes and pleiotropy with melanization in the pathogen Zymoseptoria tritici

“…This pattern follows the general paradigm that fungal isolates with greater melanization are less sensitive to fungicides (Butler and Day, 1998;Nosanchuk and Casadevall, 2006;Taborda et al, 2008), with the underlying mechanism thought to be direct binding of melanin to the fungicide (Nosanchuk and Casadevall, 2006). Although the involvement of PKS1 in DHN melanin biosynthesis and the association between melanin and fungicide resistance was already established (Butler and Day, 1998;Hu et al, 2012), we are not aware of previous work finding a direct association between PKS1 and fungicide resistance in a filamentous ascomycete. We postulate that mutations in PKS1 may explain the emergence of azole resistance in other ascomycete fungi.…”

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

“…Knock-down of a polyketide (DHN)-melanin PKS gene by RNAi or inhibition of melanin biosynthetic pathway by tricyclazole in Chaetomium globosum led to full defects in both melanin production and conidia formation (Hu et al, 2012). Similar phenotype was also observed in the maize pathogen Cochliobolus heterotrophus, in which melanization and conidiation were both under the negative control of the LaeA and VeA complexes (Wu et al, 2012).…”

Translating biosynthetic gene clusters into fungal armor and weaponry

“…In radiotrophic fungi, some evidence suggests that melanins function to enhance fungal growth via capture of ionizing radiation for energy conversion 59 . Spore pigments can also be critical in the development of normal asexual and sexual spore structures 60,61 . Deletion of sporulation-specific BGC genes can result in absolute loss of sexual development in fungi, as seen in the requirement for a polyketide for fertile structures in Sordaria macrospora 62 or the contribution of numerous SMs to development of sclerotia (sites of sexual sporulation and resistance structures to insect feeding) in Aspergillus flavus 63–65 .…”