The CsSBS1-CsTTG1 module contributes to fruit spine size via <i>CsACO2</i> -mediated ethylene biosynthesis in <i>Cucumis sativus</i> L.

Spines are an important trait of cucumber fruit that affects commercial quality, smoothness, transportation, storage, and pesticide residue retention. Spine Base Size1 (CsSBS1), a C2H2 zinc-finger transcription factor, has been identified as a determinant of cucumber fruit spine size, though its molecular mechanism remains unclear. Here, our study found that exogenous ethylene treatment partially restored the small spine base phenotype in the Cssbs1 near-isogenic line (NIL) S-SB and knockout lines, while the ethylene inhibitor aminoethoxyvinylglycine reduced spine base size in wild-type L-SB plants. Further investigation revealed that CsSBS1 directly bound to the promoter of the ethylene-biosynthesis gene 1-aminocyclopropane-1-carboxylate oxidase 2 (CsACO2) and activated its expression. Silencing CsACO2 through RNA interference inhibited fruit spine base expansion in wild-type plants, whereas enhanced CsACO2 expression resulted in larger spine bases in S-SB plants. Additionally, knockout of CsTTG1 led to smaller fruit spine bases and decreased ethylene release. Genetic and biochemical analyses indicated that CsTTG1 enhances CsSBS1-mediated transcriptional activation of CsACO2. Overall, our results reveal a CsSBS1-CsTTG1 regulatory module that regulates fruit spine base size via CsACO2-mediated ethylene biosynthesis in cucumber.