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Enhanced production of perylenequinones in the endophytic fungus Shiraia sp. Slf14 by calcium/calmodulin signal transduction

Liu, Bin, Bao, Jianying, Zhang, Zhibin, Yan, Riming, Wang, Ya, Yang, Huilin, Zhu, Du
Applied microbiology and biotechnology 2018 v.102 no.1 pp. 153-163
biosynthesis, calcium, calcium signaling, calmodulin, endophytes, gene expression regulation, genes, mycotoxins, plant pathogenic fungi, polyketides, reactive oxygen species
Perylenequinones (PQ) that notably produce reactive oxygen species upon exposure to visible light are a class of photoactivated polyketide mycotoxins produced by fungal plant pathogens such as Shiraia sp. The involvement of Ca²⁺/calmodulin (CaM) signalling in PQ biosynthesis was investigated by submerged culturing of Shiraia sp. Slf14, a species that produces hypocrellins HA and HB and elsinochromes EA, EB, and EC. Our results showed that the total content of PQ reached 1894.66 ± 21.93 mg/L under optimal conditions of Ca²⁺ addition, which represents a 5.8-fold improvement over controls. The addition of pharmacological Ca²⁺ sensor inhibitors strongly inhibited PQ production, which indicates that Ca²⁺/CaM signalling regulates PQ biosynthesis. The expression levels of Ca²⁺ sensor and PQ biosynthetic genes were downregulated following addition of inhibitors but were upregulated upon addition of Ca²⁺. Inhibition was partially released by external Ca²⁺ supplementation. Fluo-3/AM experiments revealed that similar cytosolic Ca²⁺ variation occurred under these conditions. These results demonstrated that Ca²⁺ signalling via the CaM transduction pathway plays a pivotal role in PQ biosynthesis.