Background: Actinomycete genome sequencing has disclosed a large number of cryptic secondary metabolite biosynthetic gene clusters. However, their unavailable or limited expression severely hampered the discovery of bioactive compounds. The whiB-like (wbl) regulatory genes play important roles in morphological differentiation as well as secondary metabolism; and hence the wblA so gene was probed and set as the target to activate cryptic gene clusters in deepsea-derived Streptomyces somaliensis SCSIO ZH66.Results: wblA so from deepsea-derived S. somaliensis SCSIO ZH66 was inactivated, leading to significant changes of secondary metabolites production in the ΔwblA so mutant, from which α-pyrone compound violapyrone B (VLP B) was isolated. Subsequently, the VLP biosynthetic gene cluster was identified and characterized, which consists of a type III polyketide synthase (PKS) gene vioA and a regulatory gene vioB; delightedly, inactivation of vioB led to isolation of another four VLPs analogues, among which one was new and two exhibited improved anti-MRSA (methicillin-resistant Staphylococcus aureus, MRSA) activity than VLP B. Moreover, transcriptional analysis revealed that the expression levels of whi genes (whiD, whiG, whiH and whiI) and wbl genes (wblC, wblE, wblH, wblI and wblK) were repressed by different degrees, suggesting an intertwined regulation mechanism of wblA so in morphological differentiation and secondary metabolism of S. somaliensis SCSIO ZH66.Conclusions: wblA orthologues would be effective targets for activation of cryptic gene clusters in marine-derived Streptomyces strains, notwithstanding the regulation mechanisms might be varied in different strains. Moreover, the availability of the vio gene cluster has enriched the diversity of type III PKSs, providing new opportunities to expand the chemical space of polyketides through biosynthetic engineering.

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Summary Fruit shape is an important quality and yield trait in melon. Although some fruit shape-related QTLs have been reported in melon, the target genes and the underlying mechanism remain poorly understood. Here, we identified and characterized a gene controlling fruit shape from two melon inbred lines B8 and HP22. Genetic analysis suggests that the fruit shape was controlled by a single and incompletely dominant locus, designated CmFSI8/CmOFP13. The CmFSI8/CmOFP13 gene was finely mapped to a 53.7 kb interval on chromosome 8 based on BSA-seq and map-based cloning strategies. CmFSI8/CmOFP13 encodes an OVATE family protein (OFP) and is orthologous to AtOFP1 and SlOFP20. The transcription level of CmFSI8/CmOFP13 in the ovary of HP22 was significantly higher than that in B8. Sequence analysis showed that a 12.5 kb genomic variation with retrotransposon insertion identified in the promoter was responsible for elevating the expression of CmFSI8/CmOFP13, which ultimately caused the differences in fruit shape. Moreover, ectopic overexpression of CmFSI8/CmOFP13 in Arabidopsis led to multiple phenotypic changes, including kidney-shaped leaves and shortened siliques. Taken together, we have demonstrated the involvement of an OFP protein in regulating melon fruit shape, and understanding the molecular mechanism will enable us to better manipulate melon fruit shape in breeding.