Fruit length is an important agricultural trait that directly affects product yield and commercial value.In different cucumber cultivars,there are dramatic variations in fruit length(5～40 cm).Despite several QTLs have been identified to regulate fruit length,the specific genes and the underlying mechanisms of fruit length regulation remain largely unknown in cucumber.Here,we found that a MADS-box gene CsFLR acting as an important repressor of fruit elongation.CsFLR knockdown leads to increased fruit elongation,whereas elevated expression of CsFLR results in significantly shorter fruit length in cucumber.CsFLR regulates fruit elongation through two pathways:one that inhibits PIN-FORMED(PIN1/7)-mediated auxin transport and thus reduces auxin accumulation in the fruit,and the other by repressing CsSUP-mediated cell division and cell expansion.Notably,a 3393 C-A SNP in the K domain of CsFLR appeared specifically in long-fruited North China-type cucumber and affected the in vitro protein interaction,indicating that CsFUL1 is a candidate gene subject to selection over cucumber diversification.