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Key message: A novel dwarf cucumber mutant, scp- 2, displays a typical BR biosynthesis-deficient phenotype, which is due to a mutation in CsDET2 for a steroid 5-alpha-reductase. Abstract: Brassinosteroids (BRs) are a group of plant hormones that play important roles in the development of plant architecture, and extreme dwarfism is a typical outcome of BR-deficiency. Most cucumber ( Cucumis sativus L.) varieties have an indeterminate growth habit, and dwarfism may have its value in manipulation of plant architecture and improve production in certain production systems. In this study, we identified a spontaneous dwarf mutant, super compact- 2 ( scp- 2), that also has dark green, wrinkle leaves. Genetic analyses indicated that scp- 2 was different from two previously reported dwarf mutants: compact ( cp) and super compact- 1 ( scp- 1). Map-based cloning revealed that the mutant phenotype was due to two single nucleotide polymorphism and a single-base insertion in the CsDET2 gene that resulted in a missense mutation in a conserved amino acid and thus a truncated protein lacking the conserved catalytic domains in the predicted steroid 5 α-reductase protein. Measurement of endogenous hormone levels indicated a reduced level of brassinolide (BL, a bioactive BR) in scp- 2, and the mutant phenotype could be partially rescued by the application of epibrassinolide (EBR). In addition, scp- 2 mutant seedlings exhibited dark-grown de-etiolation, and defects in cell elongation and vascular development. These data support that scp- 2 is a BR biosynthesis-deficient mutant, and that the CsDET2 gene plays a key role in BR biosynthesis in cucumber. We also described the systemic BR responses and discussed the specific BR-related phenotypes in cucumber plants. [ABSTRACT FROM AUTHOR]

We isolated a mutant showing perturbations in the development of male and female floral organs and fruits. Analysis of the single nucleotide polymorphisms from bulked F2 pools identified the causative variant occurring in Csa4G126690. Csa4G126690 shows high homology to Arabidopsis SEPALLATA2 ( SEP2) thus being designated CsSEP2. The causative variant was located on the splicing site of CsSEP2, resulting in the skipping of exon 6 and abolishment of the transcriptional activity. Our data suggest that CsSEP2 is involved in the floral organ and fruits development by conferring transcriptional activity. [ABSTRACT FROM AUTHOR]

Most fruits in our daily diet are the products of domestication and breeding. Here we report a map of genome variation for a major fruit that encompasses ∼3.6 million variants, generated by deep resequencing of 115 cucumber lines sampled from 3,342 accessions worldwide. Comparative analysis suggests that fruit crops underwent narrower bottlenecks during domestication than grain crops. We identified 112 putative domestication sweeps; 1 of these regions contains a gene involved in the loss of bitterness in fruits, an essential domestication trait of cucumber. We also investigated the genomic basis of divergence among the cultivated populations and discovered a natural genetic variant in a β-carotene hydroxylase gene that could be used to breed cucumbers with enhanced nutritional value. The genomic history of cucumber evolution uncovered here provides the basis for future genomics-enabled breeding. [ABSTRACT FROM AUTHOR]