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 qiu mutant.Compared with the cylindrical fruit shape in 32X(wild type),the fruit shape in qiu 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 FS2.1 locus reported previously.A single-nucleotide polymorphism(SNP)(11359603)causing a truncated protein of CsaV3_2G013800,the homolog of tomato fruit shape gene SlTRM5,may underlie the fruit shape variation in the qiu mutant.Knockout of CsTRM5 by the CRISPR-Cas9 system confirmed that CsaV3_2G013800/CsTRM5 was the causal gene responsible for qiu.Sectioning analysis showed that the spherical fruit in qiu 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 qiu.Transcriptome profiling showed that the expression levels of cell-wall-related genes and abscisic acid(ABA)pathway genes were significantly upregulated in qiu.Hormone measurements indicated that ABA content was greatly increased in the qiu mutant.Exogenous ABA application reduced fruit elongation by inhibiting cell expansion in cucumber.Taken together,these data suggest that CsTRM5 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.

CsRAXs negatively regulate leaf size and fruiting ability through auxin glycosylation in cucumber

Leaves are the main photosynthesis organ that directly determines crop yield and biomass.Dissecting the regulatory mechanism of leaf development is crucial for food security and ecosystem turn-over.Here,we identified the novel function of R2R3-MYB transcription factors CsRAXs in regulating cucumber leaf size and fruiting ability.Csrax5 single mutant exhibited enlarged leaf size and stem diameter,and Csrax1/2/5 triple mutant displayed further enlargement phenotype.Overexpression of CsRAX1 or CsRAX5 gave rise to smaller leaf and thinner stem.The fruiting ability of Csrax1/2/5 plants was significantly enhanced,while that of CsRAX5 overexpression lines was greatly weakened.Similarly,cell number and free auxin level were elevated in mutant plants while decreased in overexpression lines.Biochemical data indicated that CsRAX1/5 directly promoted the expression of auxin glucosyltransferase gene CsUGT74E2.Therefore,our data suggested that CsRAXs function as repressors for leaf size development by promoting auxin glycosylation to decrease free auxin level and cell division in cucumber.Our findings provide new gene targets for cucumber breeding with increased leaf size and crop yield.