Genetic Mapping of Giant Embryo Mutant and Varietal Variation of Rice Embryo

Abstract

Rice embryo provides many essential nutrients for human health as well as other valuable industrial materials, and the embryo size is also positively correlated with the contents of such salutary compounds as γ-aminobutyric acid (GABA), α-tocopherol and vitamins. Thus controlling embryo size is becoming more and more important in the field of rice breeding. We obtained three giant embryo mutants derived from Hwacheongbyeo (Korean japonica cultivar) by N-methyl-N-nitrosourea (MNU). These three mutants, embryo size of all of which were larger than that of wild type (Hwacheongbyeo), were named according to different embryo size as ge-m, ge and ge-s, from the smallest to the largest, respectively. The result of allelism test among wild type, ge-m, ge and ge-s revealed that the embryo size of ge and ge-s was controlled by the same gene (GIANT EMBRYO, GE). Through GE locus sequencing of three mutants, we found that each of ge and ge-s had a point mutation in GE locus, causing amino acid substitution in the coding region, but ge-m had no sequence alteration in the locus. We performed genetic mapping of the gene controlling ge-m phenotype and identified that the gene is located in chromosome 3 between S03p28781 and RM15758 markers. In spite of high nutritional value, most of embryos, in general, are detached from grain and lost during milling process. Therefore, increasing unstripped embryo rate (UER) is important during milling process. We conducted comparative analysis on grain and embryo traits among 49 rice varieties in order to select desirable candidates of embryo rice and to collect basic data for developing high UER variety. Correlation analysis among traits collected showed that embryo dent, which in turn is expected to affect UER was positively correlated with grain width(r=0.53**) and grain area(r=0.34*), while negative correlation with grain length to width ratio(r=-0.38**), revealing that the attached shape of embryo was influenced by the shape of grain. Likewise, it was noted that the embryo dent was mainly affected by grain width, not by grain length, and embryo dent affected to the position of embryonic shoot and radicle. Daerip 1, Jinbu, Jinbo, Heugseol, Obong, Unkwang, Cheongnam, Koshihikari, Cheonghaejinmi and Boramchan showed high embryo dent. These data and the varieties identified by this study could be useful in selecting promising varieties with high UER and developing new variety of higher UER.