Characteristic Analysis Of The "Super Compect-2" Mutant In Cucumber(Cucumis Sativus L.)

Plant type characteristics such as plant height and compact play an important role in plant lodging resistance and crop yield,and dwarfism may have its value in manipulation of plant architecture and improve production in certain production systems.Most cucumber(Cucumis sativus L.)varieties have an indeterminate growth habit.However,in this study a spontaneous dwarf mutant,super compact-2(scp-2),is identified,which provides an important test material for the study of cucumber dwarf phenotype.Through the systematic research of the mutation material,the main results are as following:1.The scp-2 mutant was different from the previously reported dwarf mutant: compact(cp).Both hypocotyl length and internode length in the scp-2 mutant are shorter than the cp mutant,and the mutant leaves are shrinking and dark green in the whole growth stages.Microscopic observation of the hypocotyl of 10-day old seedlings showed that the average cell size in the scp-2 mutant was significantly smaller than that of the WT plants;whereas no obvious difference was observed in the number of cells along the length and cross-sections of hypocotyls in the WT and scp-2 mutant.Irregular growth of the vascular system and cell shapes were also observed in the mutant,which are the typical features of BR-deficient mutants in previous studies.2.Map-based cloning revealed that the scp-2 gene is located in the cucumber genome chromosome Ⅲ.The mutant phenotype was due to two single nucleotide polymorphism and a 1-bp insertion in the CsDET2 gene.Studies have shown that CsDET2 gene can encode steroid 5α-reductase protein that is an important enzyme in early BR biosynthetic pathway.Thus the CsDET2 gene mutations cause a missense mutation in a conserved amino acid and thus a truncated protein lacking the conserved catalytic domains in the predicted steroid 5α-reductase protein.3.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.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.