The mutation of CsSUN, an IQD family protein, is responsible for the short and fat fruit (sff) in cucumber (Cucumis sativus L.).

The fruit shape of cucumber is an important agronomic trait, and mining regulatory genes, especially dominant ones, is vital for cucumber breeding. In this study, we identified a short and fat fruit mutant, named sff, from an EMS mutagenized population. Compared to the CCMC (WT), sff (MT) exhibited reduced fruit length and increased dimeter. Segregation analysis revealed that the sff phenotype is controlled by a semi-dominant single gene with dosage effects. Through map-based cloning, the SFF locus was narrowed down to a 52.6 kb interval with two SNPs (G651A and C1072T) in the second and third exons of CsaV3_1G039870, which encodes an IQD family protein, CsSUN. The G651A within the IQ domain of CsSUN was identified as the unique SNP among 114 cucumber accessions, and it was the primary cause of the functional alteration in CsSUN. By generating CsSUN knockout lines in cucumber, we confirmed that CsSUN was responsible for sff mutant phenotype. The CsSUN is localized to the plasma membrane. CsSUN exhibited the highest expression in the fruit with lower expression in sff compared to WT. Histological observations suggest that the sff mutant phenotype is due to increased transverse cell division and inhibited longitudinal cell division. Transcriptome analysis revealed that CsSUN significantly affected the expression of genes related to cell division, expansion, and auxin signal transduction. This study unveils CsSUN's crucial role in shaping cucumber fruit and offers novel insights for cucumber breeding.

A mutation in CsDWF7 gene encoding a delta7 sterol C-5(6) desaturase leads to the phenotype of super compact in cucumber (Cucumis sativus L.).

KEY MESSAGE: A novel super compact mutant, scp-3, was identified using map-based cloning in cucumber. The CsDWF7 gene encoding a delta7 sterol C-5(6) desaturase was the candidate gene of scp-3. Mining dwarf genes is important in understanding stem growth in crops. However, only a small number of dwarf genes have been cloned or characterized. Here, we characterized a cucumber (Cucumis sativus L.) dwarf mutant, super compact 3 (scp-3), which displays shortened internodes and dark green leaves with a wrinkled appearance. The photosynthetic rate of scp-3 is significantly lower than that of the wild type. The dwarf phenotype of scp-3 mutant can be partially rescued by the exogenous brassinolide (BL) application, and the endogenous brassinosteroids (BRs) levels in the scp-3 mutant were significantly lower compared to the wild type. Microscopic examination revealed that the reduced internode length in scp-3 resulted from a decrease in cell size. Genetic analysis showed that the dwarf phenotype of scp-3 was controlled by a single recessive gene. Combined with bulked segregant analysis and map-based cloning strategy, we delimited scp-3 locus into an 82.5 kb region harboring five putative genes, but only one non-synonymous mutation (A to T) was discovered between the mutant and its wild type in this region. This mutation occurred within the second exon of the CsGy4G017510 gene, leading to an amino acid alteration from Leu156 to His156. This gene encodes the CsDWF7 protein, an analog of the Arabidopsis DWF7 protein, which is known to be involved in the biosynthesis of BRs. The CsDWF7 protein was targeted to the cell membrane. In comparison to the wild type, scp-3 exhibited reduced CsDWF7 expression in different tissues. These findings imply that CsDWF7 is essential for both BR biosynthesis as well as growth and development of cucumber plants.