MYB transcription factor regulates the development of fruit spines through the ethylene pathway in cucumber

The spine, which is usually composed of a base and stalk, is an important economic trait in cucumber fruits. Although previous studies have reported that genes regulate the size of the cucumber fruit spines, the regulatory mechanism is not clear, and the genes that regulate stalk formation have not been identified. Here, we obtained Csmyb36 mutant by inducing mutagenesis using ethylmethylsulfone. This mutant exhibited two phenotypes of spines. First, in the Csmyb36 mutant, the spine base became smaller. Second, a new type of 'spine-like' trichome appeared on the mutant fruit peel. Similar results were obtained after the knockout of CsMYB36, which had the mutant trichome phenotype. The complementation line restored the spine-like phenotype, but the spine base size phenotype was not restored. pCsMYB36-GUS analysis showed that CsMYB36 was highly expressed in the fruit spine, and the expression of CsMYB36 in large spine-based cucumber varieties was higher than that in small spine-based cucumber varieties. Biochemical analyses showed that CsMYB36 interacted with CsSBS1 to regulate fruit spine size through the ethylene pathway. Two ethylene-activated signalling pathway genes were identified as candidate genes involved in spine-like formation. In conclusion, our findings indicated that CsMYB36 regulated the development of cucumber fruit spines via the ethylene pathway. Our findings provide valuable genetic resources for cucumber breeders to cultivate cucumber varieties by developing different types of fruit spines.