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

Background: 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). Results: 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. Conclusions: We confirmed that a GA biosynthetic enzyme HvGA20ox(2), 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.