CsTRM5 regulates fruit shape via mediating cell division direction and cell expansion in cucumber.

Fruit shape and size are important appearance and yield traits in cucumber, but the underlying genes and their regulatory mechanisms remain poorly understood. Here we identified a mutant with spherical fruits from an Ethyl Methane Sulfonate (EMS)-mutagenized library, named the mutant. Compared with the cylindrical fruit shape in 32X (wild type), the fruit shape in was round due to reduced fruit length and increased fruit diameter. MutMap analysis narrowed the candidate gene in the 6.47 MB range on Chr2, harboring the locus reported previously. A single-nucleotide polymorphism (SNP) (11359603) causing a truncated protein of , the homolog of tomato fruit shape gene , may underlie the fruit shape variation in the mutant. Knockout of by the CRISPR-Cas9 system confirmed that was the causal gene responsible for . Sectioning analysis showed that the spherical fruit in resulted mainly from increased and reduced cell division along the transverse and longitudinal directions, respectively. Meanwhile, the repressed cell expansion contributed to the decreased fruit length in . Transcriptome profiling showed that the expression levels of cell-wall-related genes and abscisic acid (ABA) pathway genes were significantly upregulated in . Hormone measurements indicated that ABA content was greatly increased in the mutant Exogenous ABA application reduced fruit elongation by inhibiting cell expansion in cucumber. Taken together, these data suggest that regulates fruit shape by affecting cell division direction and cell expansion, and that ABA participates in the CsTRM5-mediated cell expansion during fruit elongation in cucumber.