A CsTu ‐ TS 1 regulatory module promotes fruit tubercule formation in cucumber

Summary The fruit epidermal features such as the size of tubercules are important fruit quality traits for cucumber production. But the mechanisms underlying tubercule formation remain elusive. Here, tubercule size locus Cs TS 1 was identified by map‐based cloning and was found to encode an oleosin protein. Allelic variation was identified in the promoter region of Cs TS 1 , resulting in low expression of Cs TS 1 in all 22 different small‐warty or nonwarty cucumber lines. High Cs TS 1 expression levels were closely correlated with increased fruit tubercule size among 44 different cucumber lines. Transgenic complementation and RNA i‐mediated gene silencing of Cs TS 1 in transgenic cucumber plants demonstrated that Cs TS 1 positively regulates the development of tubercules. Cs TS 1 is highly expressed in the peel at fruit tubercule forming and enlargement stage. Auxin content and expression of three auxin signalling pathway genes were altered in the 35S:Cs TS 1 and Cs TS 1 ‐ RNA i fruit tubercules, a result that was supported by comparing the cell size of the control and transgenic fruit tubercules. CsTu, a C 2 H 2 zinc finger domain transcription factor that regulates tubercule initiation, binds directly to the Cs TS 1 promoter and promotes its expression. Taken together, our results reveal a novel mechanism in which the CsTu‐ TS 1 complex promotes fruit tubercule formation in cucumber.