Pestalotiopsis Diversity: Species, Dispositions, Secondary Metabolites, and Bioactivities

Pestalotiopsis species have gained attention thanks to their structurally complex and biologically active secondary metabolites. In past decades, several new secondary metabolites were isolated and identified. Their bioactivities were tested, including anticancer, antifungal, antibacterial, and nematicidal activity. Since the previous review published in 2014, new secondary metabolites were isolated and identified from Pestalotiopsis species and unidentified strains. This review gathered published articles from 2014 to 2021 and focused on 239 new secondary metabolites and their bioactivities. To date, 384 Pestalotiopsis species have been discovered in diverse ecological habitats, with the majority of them unstudied. Some may contain secondary metabolites with unique bioactivities that might benefit pharmacology.

A Fungal Diterpene Synthase Is Responsible for Sterol Biosynthesis for Growth

A conserved open reading frame, dps, is described in Pestalotiopsis microspora, sharing a remarkable similarity with fungal diterpene synthases whose function is less studied. Loss-of-function approach manifested that dps was necessary for the growth and the development of the fungus. A deletion strain, dpsΔ, showed a fundamental retardation in growth, which could deliberately be restored by the addition of exogenous sterols to the media. Gas chromatography-mass spectrometry analysis confirmed the loss of the ability to produce certain sterols. Thus, the tolerance and the resistance of dpsΔ to several stress conditions were impaired. Secondary metabolites, such as the polyketide derivative dibenzodioxocinones, were significantly diminished. At the molecular level, the deletion of dps even affected the expression of genes in the mevalonate pathway. This report adds knowledge about fungal diterpene synthases in Pestalitiopsis microspora.

Distinct Roles of Velvet Complex in the Development, Stress Tolerance, and Secondary Metabolism in Pestalotiopsis microspora, a Taxol Producer

The velvet family proteins have been shown to play critical roles in fungal secondary metabolism and development. However, variations of the roles have been observed in different fungi. We report here the observation on the role of three velvet complex components VeA, VelB, and LaeA in Pestalotiopsis microspora, a formerly reported taxol-producing fungus. Deletion of individual members led to the retardation of vegetative growth and sporulation and pigmentation, suggesting critical roles in these processes. The mutant strain △velB appeared hypersensitive to osmotic stress and the dye Congo red, whereas △veA and △laeA were little affected by the pressures, suggesting only velB was required for the integrity of the cell wall. Importantly, we found that the genes played distinct roles in the biosynthesis of secondary metabolites in P. microspora. For instance, the production of pestalotiollide B, a previously characterized polyketide, required velB and laeA. In contrast, the veA gene appeared to inhibit the pestalotiollide B (PB) role in its biosynthesis. This study suggests that the three components of the velvet complex are important global regulators, but with distinct roles in hyphal growth, asexual production, and secondary metabolism in P. microspora. This work provides information for further understanding the biosynthesis of secondary metabolism in the fungus.

The AMP-Activated Protein Kinase Homolog Snf1 Concerts Carbon Utilization, Conidia Production and the Biosynthesis of Secondary Metabolites in the Taxol-Producer Pestalotiopsis microspora

Highly conserved, the Snf1/AMPK is a central regulator of carbon metabolism and energy production in the eukaryotes. However, its function in filamentous fungi has not been well established. In this study, we reported functional characterization of Snf1/AMPK in the growth, development and secondary metabolism in the filamentous fungus Pestalotiopsis microspora. By deletion of the yeast SNF1 homolog, we found that it regulated the utilization of carbon sources, e.g., sucrose, demonstrating a conserved function of this kinase in filamentous fungus. Importantly, several novel functions of SNF1 were unraveled. For instance, the deletion strain displayed remarkable retardation in vegetative growth and pigmentation and produced a diminished number of conidia, even in the presence of the primary carbon source glucose. Deletion of the gene caused damages in the cell wall as shown by its hypersensitivities to Calcofluor white and Congo red, suggesting a critical role of Snf1 in maintaining cell wall integrity. Furthermore, the mutant strain Δsnf1 was hypersensitive to stress, e.g., osmotic pressure (1 M sorbitol), drug G418 and heat shock, though the mechanism remains to be illustrated. Significantly, disruption of the gene altered the production of secondary metabolites. By high-performance liquid chromatography (HPLC) profiling, we found that Δsnf1 barely produced secondary metabolites, e.g., the known product pestalotiollide B. This study suggests that Snf1 is a key regulator in filamentous fungus Pestalotiopsis microspora concerting carbon metabolism and the filamentous growth, conidiation, cell wall integrity, stress tolerance and the biosynthesis of secondary metabolites.

Amino Acid Sensor Kinase Gcn2 Is Required for Conidiation, Secondary Metabolism, and Cell Wall Integrity in the Taxol-Producer Pestalotiopsis microspora

The canonical Gcn2/Cpc1 kinase in fungi coordinates the expression of target genes in response to amino acid starvation. To investigate its possible role in secondary metabolism, we characterized a gcn2 homolog in the taxol-producing fungus Pestalotiopsis microspora. Deletion of the gene led to severe physiological defects under amino acid starvation, suggesting a conserved function of gcn2 in amino acid sensing. The mutant strain Δgcn2 displayed retardation in vegetative growth. It generated dramatically fewer conidia, suggesting a connection between amino acid metabolism and conidiation in this fungus. Importantly, disruption of the gene altered the production of secondary metabolites by HPLC profiling. For instance, under amino acid starvation, the deletion strain Δgcn2 barely produced secondary metabolites including the known natural product pestalotiollide B. Even more, we showed that gcn2 played critical roles in the tolerance to several stress conditions. Δgcn2 exhibited a hypersensitivity to Calcofluor white and Congo red, implying a role of Gcn2 in maintaining the integrity of the cell wall. This study suggests that Gcn2 kinase is an important global regulator in the growth and development of filamentous fungi and will provide knowledge for the manipulation of secondary metabolism in P. microspora.

The Gα1-cAMP signaling pathway controls conidiation, development and secondary metabolism in the taxol-producing fungus Pestalotiopsis microspora

G-protein-mediated signaling pathways regulate fungal morphogenesis, development and secondary metabolism. In this study, we report a gene, pgα1, that putatively encodes the α-subunit of a group I G protein in Pestalotiopsis microspora NK17, which is known to produce various secondary metabolites, including the antitumor drug taxol and pestalotiollide B (PB). Mutants of pgα1 showed retarded vegetative growth, aging of the mycelium, premature conidiation, deformed conidia, significantly increased melanin production, and a sharp decrease in PB production. The introduction of extra copies of pgα1 led to a different phenotype that was characterized by enhanced production of PB. qRT-PCR revealed that the expression of pks1, which encodes melanin polyketide synthase, an enzyme that is involved in 1, 8-dihydroxynaphthalene (DHN) melanin biosynthesis, was up regulated by 55-fold in the absence of pgα1. Changes in conidiation and PB production in pgα1 mutants were able to be restored by the addition of exogenous cAMP. The deficiencies of PB production and conidiation in Δpgα1 were not able to be rescued by deletion or overexpression of a previously reported histone deacetylase gene (hid1), suggesting that pgα1 is able to override the effect of hid1 on PB production and conidiation. Our results suggested that the G protein-cAMP pathway plays a critical role in vegetative growth as well as in asexual development of P. microspora.

Improved pestalotiollide B production by deleting competing polyketide synthase genes in Pestalotiopsis microspora

Pestalotiollide B, an analog of dibenzodioxocinones which are inhibitors of cholesterol ester transfer proteins, is produced by Pestalotiopsis microspora NK17. To increase the production of pestalotiollide B, we attempted to eliminate competing polyketide products by deleting the genes responsible for their biosynthesis. We successfully deleted 41 out of 48 putative polyketide synthases (PKSs) in the genome of NK17. Nine of the 41 PKS deleted strains had significant increased production of pestalotiollide B (P < 0.05). For instance, deletion of pks35, led to an increase of pestalotiollide B by 887%. We inferred that these nine PKSs possibly lead to branch pathways that compete for precursors with pestalotiollide B, or that convert the product. Deletion of some other PKS genes such as pks8 led to a significant decrease of pestalotiollide B, suggesting they are responsible for its biosynthesis. Our data demonstrated that improvement of pestalotiollide B production can be achieved by eliminating competing polyketides.

A B-type histone acetyltransferase Hat1 regulates secondary metabolism, conidiation, and cell wall integrity in the taxol-producing fungus Pestalotiopsis microspora

In filamentous fungi, many gene clusters for the biosynthesis of secondary metabolites often stay silent under laboratory culture conditions because of the absence of communication with its natural environment. Epigenetic processes have been demonstrated to be critical in the expression of the genes or gene clusters. Here, we report the identification of a B-type histone acetyltransferase, Hat1, and demonstrate its significant roles in secondary metabolism, conidiation, and the cell wall integrity in the fungus Pestalotiopsis microspora. An hat1 deletion strain shows a dramatic decrease of SMs in this fungus, suggesting hat1 functions as a global regulator on secondary metabolism. Moreover, the mutant strain hat1Δ delays to produce conidia with significantly decreased number of conidia, while shows little effect on vegetative growth, suggesting that it plays a critical role in conidiation. The hypersensitivity of hat1Δ to Congo red demonstrates that disruption of hat1 impairs the integrity of cell wall. Overexpression of the wild-type hat1 allele enhances conidiation by boosting the number of conidia. This is the first report on the role of a B-type histone acetyltransferase in fungal secondary metabolism and cell wall integrity.