The CsHEC1-CsOVATE module contributes to fruit neck length variation via modulating auxin biosynthesis in cucumber.

Abstract

Fruit neck is the proximal portion of the fruit with undesirable taste that has detrimental effects on fruit shape and commercial value in cucumber. Despite the dramatic variations in fruit neck length of cucumber germplasms, the genes and regulatory mechanisms underlying fruit neck elongation remain mysterious. In this study, we found that <i>Cucumis sativus HECATE1</i> (<i>CsHEC1</i>) was highly expressed in fruit neck. Knockout of <i>CsHEC1</i> resulted in shortened fruit neck and decreased auxin accumulation, whereas overexpression of <i>CsHEC1</i> displayed the opposite effects, suggesting that <i>CsHEC1</i> positively regulated fruit neck length by modulating local auxin level. Further analysis showed that CsHEC1 directly bound to the promoter of the auxin biosynthesis gene <i>YUCCA4</i> (<i>CsYUC4</i>) and activated its expression. Enhanced expression of <i>CsYUC4</i> resulted in elongated fruit neck and elevated auxin content. Moreover, knockout of <i>CsOVATE</i> resulted in longer fruit neck and higher auxin. Genetic and biochemical data showed that CsOVATE physically interacted with CsHEC1 to antagonize its function by attenuating the CsHEC1-mediated <i>CsYUC4</i> transcriptional activation. In cucumber germplasms, the expression of <i>CsHEC1</i> and <i>CsYUC4</i> positively correlated with fruit neck length, while that of <i>CsOVATE</i> showed a negative correlation. Together, our results revealed a CsHEC1-CsOVATE regulatory module that confers fruit neck length variation via <i>CsYUC4</i>-mediated auxin biosynthesis in cucumber.