Genetic Mapping of a Rice Loose Upper Panicle Mutant

We identified a loose upper panicle mutant (lup) from a japonica-type rice variety, Hwacheongbyeo, treated by Ethyl Methane Sulfonate (EMS). The lup mutant displayed an increased distance between spikelets particularly in the first primary branches, and the number of spikelet was reduced. In addition, aborted spikelets in the tip of first primary branches were observed. Besides these morphological changes in the panicle, the lup mutant also displayed overall reduction in culm length, panicle length, grain weight, and tiller number. On the contrary, the chlorophyll content was relatively high in lup mutant in comparison to wild-type plants, and displayed a “stay-green” phenotype even after physiological maturity. Genetic analysis (using F2 population of lup/M.23) revealed that a single recessive gene is involved in the above-mentioned morphological changes in the lup mutant. A candidate genomic region was fine-mapped at an interval of 1.04 Mb flanked by two molecular markers, 18170 and D0052, on the long arm of chromosome 8. In this region, we found a total of 348 mutation points using a slightly modified MutMap method. Based on these results, we expect the candidate genomic region containing a putative LUP gene will provide an important clue in developmental regulation of spikelets and panicle in rice.