The formation of propagules (conidia and ascospores) is the critical stage for the transmission of the pathogenic fungus Stemphylium eturmiunum. However, how the development of these propagules is regulated remains to be fully understood. Here, we show that nitric oxide (NO) is necessary for the formation of conidia and pseudothecia in S. eturmiunum. Application of NO scavenger carboxy-CPTIO (cPTIO) or soluble guanylate cyclase (sGC) inhibitor NS2028 abolishes the formation of conidia and pseudothecia. In the culture of S. eturmiunum, supplement of NO-releasing compound sodium nitroprusside (SNP) results in an increased formation of conidia at 0.2 mmol/L, and pseudothecia at 2 mmol/L. SNP supplement also triggered increased biosynthesis of melanin, which can be inhibited partially upon the addition of either arbutin or tricyclazole, the specific inhibitors for 3,4-dihydroxyphenylalanine (DOPA) and dihydroxynaphthalene (DHN) synthetic pathway, respectively. Intriguingly, enhanced melanin biosynthesis triggered an increased formation of propagules; while its inhibition impaired their formation. The SNP-induced increment in the formation of propagules can be also compromised upon supplement of cPTIO or NS-2028. RT-PCR analysis showed that SNP at 0.2 mmol/L promoted transcription of the genes encoding the conidiation co-regulators brlA, abA, and wetA, and inhibited at 2 mmol/L. In contrast, application of SNP at 2 mmol/L increased transcription of the genes encoding mat1, and mat2, the genes related to sexual reproduction, and the transcription of two DNH melanin synthetic genes pks1 and pks2, and the key gene tyr for DOPA melanin biosynthesis. However, the increased transcription of these genes is down-regulated or blocked upon supplement of cPTIO or NS-2028. Thus, NO regulates asexual and sexual development, as well as melanin synthesis in S. eturmiunum possibly through NO-sGC-GMP signaling pathway.

Talarolactone C (1), Talarolactone A (2), Talarolactone B (3, sulfoxide derivative), and Talarolactone D (4, sulfone derivative) were isolated from Talaromyces sp. which was cultured in rice medium with sodium butyrate. The structures of talarolactone analogs above were characterized by a combination of spectroscopic, X-ray crystallographic, and computational methods. These talarolactones and Talarolactone A sodium (5) with the same carbon skeleton showed different fluorescence characteristics.