Genetic and molecular analysis of utility of sd1 alleles in rice breeding

The widespread adoption of the high-yielding semi-dwarf rice variety, IR8, led to the "green revolution" in Asia in the 1960s. The short stature of this variety is due to a loss-of-function of the SD1 gene that encodes a GA20 oxidase-2 (GA20ox-2) which catalyzes late steps of gibberellin biosynthesis. In this study, we investigated how widely sd1 mutations have been employed in the generation of semi-dwarf varieties of rice. Genetic and molecular analyses revealed that the sd1 allele of IRS has been used in the production of japonica varieties. Sequence analysis of the SD1 locus of 57 semi-dwarf varieties showed that at least 7 sd1 alleles have been used in the breeding of semi-dwarf rice varieties in China, USA and Japan. The utilization of such a high number of different alleles all controlling the same target trait highlights that mutations in GA20ox-2 induce an agronomically advantageous architecture in rice.