Changes in catechin contents and expression of catechin biosynthesis-associated genes during early cucumber fruit development

Cucumber (Cucumis sativus L.), a biologically, agriculturally, and economically important vegetable crop consumed worldwide. Catechins (Cs) are the main astringent substances that affect the oral sensory quality of cucumber fruit, and they exhibit potential human health benefits in the amelioration of chronic diseases. However, little is known about the primary components of Cs or their regulatory mechanisms in cucumber. In this study, dynamic changes in C levels and the expression patterns of C-related genes in the peel and flesh of cucumber inbred line ‘YB’, which is strongly astringent during the early fruit development period, were examined. Only three types of Cs, gallocatechin, C and epigallocatechin gallate, were detectable in cucumber fruit, and their contents decreased with fruit development. Gallocatechin was the major C and was present in significantly greater concentrations in peel than in flesh. The expression profiles of 38 genes related to C biosynthesis were investigated by qRT-PCR. We hypothesized that CsPAL3, CsPAL5, CsC4H1, Cs4CL2, CsCHS2, CsCHI2, CsDFR2, CsF3H3, and CsANS are the important C biosynthesis regulators in cucumber fruit. The isolation of genes encoding biosynthetic enzymes provides important molecular resources for further genetic manipulations of C biosynthesis in cucumber.