Variation in CRABS CLAW (CsCRC) contributes to fruit length modulation in cucumber

Fruit length is a key domestication trait that affects crop yield and appearance quality. Cucumber fruits vary from 5~60 cm in length. Despite multiple fruit length QTLs have been identified, the underlying genes and regulatory mechanisms are poorly understood. Map-based cloning identified a nonsynonymous SNP (G to A) in CRABS CLAW (CsCRC) confers the major effect fruit length QTL FS5.2. CsCRCA is a rare allele only exist in Xishuangbanna cucumber with round fruits. Construction of near-isogenic line (NIL) of CsCRCA led to 34~39% reduction in fruit length. Introduction of CsCRCG into the NIL rescued the short-fruit phenotype, and knockdown of CsCRCG resulted in reduced fruit length and decreased cell size. RNA-seq results showed that an auxin responsive protein CsARP1 expressed decreased in CsCRC-RNAi lines. Further, an auxin responsive protein Further, CsARP1 is the downstream target gene of CsCRCG, instead of CsCRCA. Knockout of CsARP1 produced decreased fruit length with smaller cells. Hence, our work suggested that CsCRCG positively regulates fruit elongation through transcriptional activation of CsARP1 and thus enhanced cell expansion. Utilization of CsCRC alleles provides a new strategy to manipulate fruit length in cucumber breeding. Fruits at anthesis from R1461 and Ci transgenic plants were used as samples for RNA sequencing. Two biological replicates were prepared for each sample