Secondary Metabolites of the Rice Blast Fungus Pyricularia oryzae: Biosynthesis and Biological Function

Abstract

Plant pathogenic fungi produce a wide variety of secondary metabolites with unique and complex structures. However, most fungal secondary metabolism genes are poorly expressed under laboratory conditions. Moreover, the relationship between pathogenicity and secondary metabolites remains unclear. To activate silent gene clusters in fungi, successful approaches such as epigenetic control, promoter exchange, and heterologous expression have been reported. Pyricularia oryzae, a well-characterized plant pathogenic fungus, is the causal pathogen of rice blast disease. P. oryzae is also rich in secondary metabolism genes. However, biosynthetic genes for only four groups of secondary metabolites have been well characterized in this fungus. Biosynthetic genes for two of the four groups of secondary metabolites have been identified by activating secondary metabolism. This review focuses on the biosynthesis and roles of the four groups of secondary metabolites produced by P. oryzae. These secondary metabolites include melanin, a polyketide compound required for rice infection; pyriculols, phytotoxic polyketide compounds; nectriapyrones, antibacterial polyketide compounds produced mainly by symbiotic fungi including endophytes and plant pathogens; and tenuazonic acid, a well-known mycotoxin produced by various plant pathogenic fungi and biosynthesized by a unique NRPS-PKS enzyme.

Phytotoxic Secondary Metabolites from Fungi

“…Pyricuol (247) exhib-ited stronger phytotoxic activity toward rice than pyriculol (244) and dihydropyriculol (245) [182]. It has been shown that aldehyde derivatives induced lesion-like necrosis on rice leaves, while alcohol derivatives were inactive [183]. Epipyriculol (246) was isolated from the cultures of Pyricularia oryzae.…”

The zinc finger protein StMR1 affects the pathogenicity and melanin synthesis of Setosphaeria turcica and directly regulates the expression of DHN melanin synthesis pathway genes

“…The secondary metabolites in Pyricularia oryzae, including melanin and phytotoxic pyriculols, are both required for the infection (Motoyama, 2020). Glyoxylate and dicarboxylate metabolism and lipid metabolism can provide important metabolic intermediates and energy for the development of fungi.…”

“…Secondary metabolites produced by plant pathogenic fungi play an important role in pathogenicity during pathogenic interactions with plants (Macheleidt et al., 2016). The secondary metabolites in Pyricularia oryzae , including melanin and phytotoxic pyriculols, are both required for the infection (Motoyama, 2020). Glyoxylate and dicarboxylate metabolism and lipid metabolism can provide important metabolic intermediates and energy for the development of fungi.…”

Three New Derivatives of Zopfinol from Pseudorhypophila Mangenotii gen. et comb. nov.

“…The structures of these compounds are related to zopfinol, but most of them were not active, except for one of the salicylaldehyde derivatives, which showed weak activity against Mycobacterium tuberculosis and Bacillus cereus [ 54 ]. Other compounds with structures related to zopfinol and its derivatives are the salicylaldehyde sordarial produced by Neurospora crassa , which also belongs to the order Sordariales [ 55 ], and the pyriculols, which are phytotoxic polyketides produced by the sordariomycete phytopathogenic fungus Pyricularia oryzae [ 56 ]. Since the phytotoxic pyriculol [ 57 ] differs from 2 only in the length of its aliphatic side chain, it would be highly interesting to test the phytotoxicity of zopfinols.…”