Single nucleotide substitution in the CsDET2 gene leads to complex alterations in plant architecture and affects brassinosteroid profile in cucumber (Cucumis sativus L.)0.

Most cucumber (Cucumis sativus L.) cultivars are characterized by indeterminate and vigorous growth, which requires a large cultivation area and increased labor for crop maintenance. Manipulating plant architecture may help optimize cucumber production in certain cultivation systems. The objective of this study was to identify the gene associated with phenotypic changes of the short petiole-2 (sp-2) mutant, which was discovered from EI (ethylenimine)-induced mutagenesis population. The line carrying the sp-2 gene was characterized by dwarf growth and dark-green wrinkled leaves with short petioles, while maintaining fertility and reproductive capacity. Genome-wide mapping using the F2:3 population developed from a cross between line B10DH, characterized by an indeterminate type of growth and undisturbed leaf and petiole development, and the line sp-2, revealed that a single nucleotide substitution in the cucumber ortholog of DE-ETIOLATED 2 (CsDET2), encoding 5α-steroid reductase, one of the early step enzymes in the brassinosteroid biosynthesis pathway, is responsible for the line sp-2 phenotype. Observed change in CsDET2 results in arginine to tryptophan substitution in the conserved CsDET2 C-terminal reductase domain. Since brassinosteroids are involved in numerous aspects of plant development, the change in a catalytic domain of a key factor involved in BR metabolism resulted in feedback effects that could be observed as deregulation of other genes involved in BR biosynthesis, as well as profound changes in the accumulation of particular BR forms in the sp-2 line. Our study reveals a role of CsDET2 in shaping plant architecture and demonstrates how a single-nucleotide change can disrupt BR biosynthesis and alter plant growth habit.