Characterization and fine mapping of a shortened uppermost internode mutant in rice

Internode elongation is an important agronomic trait in rice that is associated with lodging, yield, flooding adaptation, and hybrid seed production. We identified a novel rice mutant line showing a shortened uppermost internode among the rice Ac/Ds insertional mutant population and named it shortened uppermost internode 4 (sui4). Interestingly, T1 plants of this line segregated into three phenotypes: extremely shortened uppermost internode-type, normal wild-type, and intermediate-type. The phenotypes of F1 plants and F2 plants from the cross of sui4 with its original variety, Dongjin, indicated that the SUI4 gene shows incomplete dominance or semidominance. Because the Ds genotypes did not co-segregate with the sui4 phenotypes, we performed mapping of this gene with 273 F2 plants from a cross between sui4 and Milyang23. Primary mapping revealed that the SUI4 locus was located between the S07012 and S07015 markers on rice chromosome 7. Further fine mapping with 36 F3 lines derived from F2 plants that have recombination in this region narrowed down the location of SUI4 to the 1.1-Mbp interval of RM1253-S07015.