Gene regulatory network of carpel number variation in cucumber

Abstract

The WUSCHEL-CLAVATA3 pathway genes play essential role in shoot apical meristem maintenance and floral organ development, and under intense selection during crop domestication. The carpel number is an important fruit trait affecting fruit shape, size, and internal quality in cucumber, but the molecular mechanism remains elusive. Here, we found that CsCLV3 expression was negatively correlated with carpel number in cucumber cultivars. CsCLV3-RNAi led to increased number of petals and carpels, whereas overexpression of CsWUS resulted in more sepals, petals and carpels, suggesting that CsCLV3 and CsWUS function as a negative and a positive regulator for carpel number variation, respectively. Biochemical analyses indicated that CsWUS directly binds to the promoter of CsCLV3 and activates its expression. Overexpression of CsFUL1A, a FRUITFULL-like MADS-box gene, resulted in more petals and carpels. CsFUL1A can directly bind to CsWUS promoter to stimulate its expression. Further, we found that auxin participates in carpel number variation in cucumber through interaction of CsARF14 with CsWUS. Therefore, we identified a gene regulatory pathway involving CsCLV3, CsWUS, CsFUL1A and CsARF14 in determining carpel number variation in an important vegetable crop-cucumber.