Molecular characterization and functional analysis of barley semi-dwarf mutant Riso no. 9265.

sdw1/denso is one of the most important and useful semi-dwarf genes in barley breeding. At least four sdw1/denso alleles have been reported and HvGA20ox 2 is considered as the candidate gene. Up to date, results of studies have not univocally proven the genetic relationship between sdw1/denso and HvGA20ox 2 . In the present study, a complete deletion of Morex_contig_40861 including both HvGA20ox 2 and Mloc_56463 genes was identified at the sdw1 locus from a semi-dwarf mutant Riso no. 9265. Expression of the genes encoding gibberellin biosynthesis (HvGA20ox 1 and HvGA3ox 2 ) were increased in the mutant compared to the wild type Bomi, while the expression of GA catabolic gene HvGA2ox 3 was decreased. Over-expression of HvGA20ox 2 could rescue the semi-dwarf phenotype and increase GAs concentration. We confirmed that a GA biosynthetic enzyme HvGA20ox2, acted as GA 20-oxidase, is the functional gene for the sdw1/denso semi-dwarfism. Lose of HvGA20ox 2 is partially compensated by HvGA20ox 1 and further feedback is regulated by gibberellin. We also deduced that the sdw1/denso allele itself affects later heading owing to its reduced endogenous GAs concentration.