Hybrid sterility is a critical barrier of inter-subspecific crosses in rice. However, hybrid sterility can be overcome by wide compatibility variety. The HWC-line of rice had slender grain shape, tall culm length, wide compatibility with both indica and japonica cultivars. For QTL analysis of HWC-line, two F2 populations were derived from the crosses between the HWC-line and each of two Korean variety, Dasan (Korean Tongil-type cultivar) and Hwacheong (temperate japonica cultivar). In the cross between HWC-line/Dasan (HD), 93 STS markers and 13 SSR markers were mapped on 12 chromosomes. In the population from HWC-line/Hwacheong (HH) cross, 28 STS markers, 29 SSR markers and 1 FNP marker were mapped on 11 chromosomes. Eight agronomic characters were evaluated for QTL analysis in two F2 populations and parents. The F2 population from HD cross revealed 21 M-QTLs and 3 E-QTL for culm length, spikelet per panicle, spikelet fertility, grain length, grain width, grain shape and 100 grains weight. 8 QTLs of culm length, grain length, grain width and grain shape were newly detected in this study. In the F2 population from HH cross, 17 M-QTLs were detected for culm length, panicle length, spikelet fertility, grain length, grain width, grain shape and 100 grains weight. 6 QTLs of culm length, grain length, grain width and grain shape were newly found in this study. These QTLs will be able to provide basic information on putative functional genes related with agronomic characters and promote breeding new rice cultivar. HWC-line could be used as bridge for inter-subspecies crosses and in hybrid breeding.

Rice hulls remain closed throughout the ripening period to maintain internal humidity of the grains. An Open-hull sterile mutant was induced by N-methyl-N-nitrosourea(MNU) treatment on Sinsunchalbyeo rice, a japonica type. This mutant showed open hulls even in the ripening stages and fully mature grains. In addition, several altered characteristics were observed, including of narrowed palea, decreased grain size, partial pollen sterility and erect panicle. Microscopic analysis showed that the palea was positioned slightly inside the lemma, and the size of palea decreased in the mutant. Genetic analysis of F2 and F3 segregation populations derived from the cross between the Open-hull sterile mutant (Oryza sativa ssp. japonica) and Milyang23 (O. sativa ssp. indica) indicated that the Open-hull trait was controlled by a single recessive allele. The fine-mapping with STS (sequence tagged site) markers revealed that the mutant gene was located on the short arm of chromosome 3. We were able to narrow it down until 30.6Kb where three candidate genes were found.

Off-type rice plants occurring in farm fields cause yield loss due to competition with cultivated rice, in addition to hindering field management and harvest work. This study aimed to observe the agronomic characteristics and trace the origins of off-type rice plants using molecular markers. A total of 116 rice accessions, comprising 35 off-type plants collected from Korean farm fields, 19 Korean commercial cultivars, 12 Korean land races, and 50 weedy rice collections, were phenotyped and genotyped using selected SSR and Subspecies Specific (SS)-STS markers. The results showed that the plant height, culm length, and leaf length of off-type rice plants were larger than those of cultivated rice, which is the typical phenotype of weedy rice. However, off-type plants were highly sterile, as opposed to weedy rice, which were highly fertile. Genotype analysis with SSR and SS-STS markers revealed that off-type rice plants were heterozygous at most of the tested marker loci, suggesting that the off-type rice plants may have originated from natural outcrossing. The genotypes of off-type rice plants were closely related to both weedy and cultivated rice, and the phylogenetic analysis revealed that the relationship of the clustered group of offtype rice plants is intermediate between Indica type weedy rice and Japonica type commercial varieties. These results suggested that off-type rice plants collected in Korean farm fields might have originated from natural outcrossing between Indica type weedy rice and the cultivated Japonica type commercial varieties.

As the market demand on functionality rice has been increasing, embryo rice in which embryo residue remains even after milling has come to comsumers’ attention because rice embryo contains several functionality components. Consequently, development of rice varieties for higher rate of embryo adhesion to grains after milling has become one of the breeding objectives for quality improvement. In this study, we observed embryo dent of 49 commercial varieties and analyzed the relationship between embryo dent and grain size and shape. Embryo dent of rice grains varied 0.27 (Keunnun)~0.59 (Daerip 1) mm. Varieties Jinbu, Jinbo, Heugseol, Obong, Unkwang, and Cheongnam showed relatively deeper embryo dent, suggesting that they will be applicable in breeding for embryo rice. Embryo dent was correlated positively with grain width (r=0.53**) and grain size(r=0.34*), and negatively with grain width/length ratio (r= -0.38**). Strategies for breeding embryo rice were discussed in relation to embryo dent, grain size and shape.

β-carotene hydroxylase (BCH) has been implicated as a key enzyme conferring a stress tolerant mechanism in plants by production of carotenoids, which serve as protectants against photoinhibition and precursor of ABA biosynthesis. We previously cloned a gene encoding a novel cytosolic form of BCH (GmBCH1) from soybean (Glycine max) whose expression increased during nodulation with Bradyrhizobium japonicum. In the present work we extended our study to three GmBCHs as soybean is an allotetraploid, and examined their possible role(s) in nodule development. In situ hybridization revealed the expression of three GmBCHs (GmBCH1, GmBCH2, and GmBCH3) in the infected cells of root nodules, and their enzymatic activities were confirmed by functional assays in E. coli. Localization of GmBCHs by transfecting Arabidopsis protoplasts with GFP fusions and by EM immunogold detection in soybean nodules indicated that GmBCH2 and GmBCH3 were present in plastids while GmBCH1 appeared to be cytosolic. RNAi of the GmBCHs severely impaired nitrogen fixation as well as nodule development. Surprisingly, we failed to detect zeaxanthin, a product of GmBCH, or any other carotenoids, in nodules. We therefore examined the possibility that most of the carotenoids in nodules are converted or cleaved to other compounds. We detected the expression of some carotenoid cleavage dioxygenases (GmCCDs) in wild-type nodules, and also a reduced amount of zeaxanthin in GmCCD8-expressing E. coli, suggesting cleavage of the carotenoid. In view of these findings we propose that carotenoids such as zeaxanthin synthesized in root nodules are cleaved by GmCCDs, and we discuss the possible roles of the carotenoid cleavage products in nodulation.

Recent global warming and climate change has presented greater challenge to the global agriculture of having to cope with more severe adversaries from various abiotic stress conditions including drought, cold, and heat. As a preliminary step towards developing a heat-tolerant japonica rice variety through molecular breeding, we examined and compared expression of several genes that have been reported being expressed specifically during rice panicle development in different rice varieties after subjecting them heat stress. Although the induction of these transcripts upon heat treatment was invariably observed in all rice varieties tested, the magnitude and kinetics of the induction were found to be different among these varieties, suggesting possible functional implication of these genes in conferring heat tolerant phenotype during reproductive organ development of these plants. General protein synthesis activity as well as pollen viability incurred by the heat stress treatment were also monitored in these plants and the result showed a close correlation overall with the induction dynamic of these transcripts under heat stress. Therefore, these genes, together with the ones involved in the regulatory network for the expression of them, could serve as candidates for useful markers with which molecular breeding of heat tolerant japonica rice can be facilitated.

The early senescence mutant was isolated from the japonica rice Koshihikari through Ethyl-methane-sulfonate (EMS) mutagenesis. The early senescence phenotype was controlled by a single recessive gene, tentatively symbolized as es-k. Using an F2 population derived from a cross between the mutant and Milyang23 and molecular markers, we mapped the es-k locus to the long arm of chromosome 7 between STS markers 147-1 and 147-2 with a physical distance of 66-kb. The symptom of early senescence appeared even before heading, while appeared during ripening in wild-type. Physiological characteristics of the es-k mutant before initiation of senescence was similar to the wild-type. However, after heading, es-k mutants started to exhibit a significant decrease in chlorophyll and soluble protein content compared to the wild-type. The wild-type leaf color appeared normal irrespective of temperature treatment, while the leaf of es-k mutant appeared pale-green at the low temperature and dark-green at the high temperature. During dark-induced senescence, mutant did not show significant differences compared to normal type. The results show that es-k is sensitive to temperature but not to light.

This study aims to identify major quantitative trait loci (QTL) for yield components under low-input systems in tropical regions in rice. A total of 156 highly advanced recombinant inbred lines (RILs) have been developed from a cross between two temperate rice varieties, Dasanbyeo (Tongil-type indica) and TR22183 (japonica). Both parental lines and RILs were tested under two different regimes of irrigation and phosphorus (P) application levels. During the wet season of 2012, under mild drought conditions, TR22183 showed more vigorous root growth at 15 days after sowing than Dasanbyeo. The early root establishment of TR22183 may have contributed to the enhanced P uptake from the top soil in the early growth stage. The linkage map for DT-RILs was constructed with 312 single nucleotide polymorphism markers aided by 384-plex platform of BeadXpress high-throughput genotyping system. For the vegetative growth, major QTLs on chromsome 6 for plant height and tiller numbers were identified. For the grain yield related traits, major QTLs on chromsome 2 were closely linked to each other. On the other hand, panicle length QTLs were identified on chromsomes 2 and 9. We are currently analyzing phenotypic data and the experiment is being repeated in dry season and temperate region.

Plant height is an important agronomic trait that affects grain yield. Previously, we reported a novel semi-dominant dwarf mutant, D-h, derived from chemical mutagenesis using N-methyl-N-nitrosourea(MNU) on a japonica rice cultivar, Hwacheongbyeo. In this study, we cloned the gene responsible for the dwarf mutant using the map-based approach. Fine mapping revealed that the mutant gene was located on the short arm of chromosome 1 in a 48 kb region. Sequencing of the candidate genes and rapid amplification of cDNA ends-polymerase chain reaction(RACE-PCR) analyses identified the gene, d-h, which encodes a protein of unknown function, but whose sequence is conserved in other cereal crops. Real-time (RT)-PCR analysis and promoter activity assay showed that the d-h gene was primarily expressed in the nodes and the panicle. In the D-h mutant plant, the gene was found to carry a 63-bp deletion in the ORF region, which was confirmed to be directly responsible for the mutant’s gain of a functional phenotype by subsequent transgenic experiments. Since the mutant plants exhibit a defect in the GA response, but not in the GA synthetic pathway, it appears that the d-h gene may be involved in a GA signaling pathway.

The architecture of rice panicle is primarily determined by the arrangement of branches and spikelets, and it directly affects grain yield. We identified a mutant for panicle apical abortion from a japonica cultivar Hwacheongbyeo treated with N-methyl-N-nitrosourea. Under normal growth conditions, the mutant had multiple abnormal phenotypes, such as a slight reduction in plant height, narrow and dark green leaf blades, and small erect panicles with clear panicle apical abortion compared to the wild-type plants. Genetic analysis revealed that the panicle apical abortion was controlled by a single recessive gene, which is tentatively designated as paa. The paa gene was fine mapped at an interval of 71 kb flanked by STS markers aptn3 and S6685-1 at the long arm of chromosome 4. Sequence analysis of the candidate genes within the delimited region showed a single base-pair change corresponding to an amino acid substitution from glycine to glutamic acid. We expect that the paa gene will be a clue to uncover the molecular mechanism of panicle apical abortion and to maintain the panicle identity for grain yield in rice breeding programs.

근래 쌀의 건강기능성에 대한 관심이 고조되면서 백미상태에서도 배아의 일부가 부착된 배아미의 이용을 위한 기술적 품종적 연구가 착수되고 있다. 본 연구는 다양한 종자형태를 보이는 49개의 품종에 대하여 현미 상태에서의 배아함몰도 및 종자형태와의 관련성에 대해 조사 분석한 것이다. 배아함몰도는 0.27(큰눈벼)～0.59(대립벼1) mm의 변이를 보였다. 49개의 품종 중 진부, 진보, 흑설, 오봉, 운광, 청남 등이 배아함몰도가 상대적으로 높은 품종이었다. 배아함몰도는 현미의 폭과는 정의 상관관계가 있었고 장폭비와는 부의 상관관계를 보여주었다. 배아함몰도가 높은 품종 육성을 위한 방향을 논의하였다.

In order to cope with the recent global warming and climate change that is projected to have a grave impact on agriculture worldwide, we will direct our focus on developing crops tolerant to multiple abiotic stresses including drought, cold and heat, with the following research activities conducted by three different research groups including an international research team at IRRI. 1) Development of heat/cold tolerant rice variety : Major genes conferring heat tolerance and cold resistance in rice will be identified by comparative transcriptome analyses and new molecular markers will be developed based upon these data. EMS mutagenesis and proteomics analyses will accompany this approach to supplement this gene identification and marker development efforts. Once reliable markers are obtained in this way, new varieties of heat/cold tolerant japonica rice will be bred through introgression of these genes. 2) Development of drought/heat tolerant rice variety : Through QTL mapping conducted on RILs between a drought resistant line and an elite line, genes conferring drought/heat tolerance will be identified and molecular markers will be developed using SNP/GBS genotyping methods. Using these markers, new rice varietis with drought/heat tolerance will be bred by employing marker assisted selection (MAS) as well as marker assisted backcross (MABC). 3) Identification of genes involved in multiple stress responses in ginseng and brassica : Molecular breeding of stress tolerance traits in ginseng and brassica is not well established to date. Taking advantage of the ginseng whole genome sequence data information and other comparative genomics approaches, members of the stress-response transcription factor family CBF/DREB will be identified and their functional analyses will be performed in ginseng and brassica using transcriptome profiling of both wild type and transgenic plants including the adventitious root-derived transgenic ginseng. Major Publications: - Lee, J., W. Jiang, et al. (2011). “Shotgun proteomic analysis for detecting differentially expressed proteins in the reduced culm number rice.” Proteomics 11(3): 455-468. - Ji, H., S. R. Kim, et al. (2010). “Inactivation of the CTD phosphatase-like gene OsCPL1 enhances the development of the abscission layer and seed shattering in rice.” The Plant journal 61(1): 96-106. - Chin JH, Gamuyao R, Dalid C, Bustamam M, Prasetiyono J, Moeljopawiro S, Wissuwa M, Heuer S (2011) Developing rice with high yield under P-deficiency: Pup1 sequence and application. Plant Physiology 156: 1-15. - Hong-Il Choi, Nam Hoon Kim et al. (2011) Development of Reproducible EST-derived SSR Markers and their application for genomics and breeding of Panax ginseng Journal of Ginseng Research 35(4): 399-412.

Hybrid sterility is one of the major barrier to the application of wide crosses in plant breeding and is commonly encountered in crosses between indica and japonica rice varieties. Ten mapping populations comprised of two reciprocal F2 and eight BC1F1 populations generated from the cross between Ilpumbyeo (japonica) and Dasanbyeo (indica) were used to identify QTLs and to interpret the gametophytic factors involved in hybrid fertility or sterility between two subspecies. Frame maps were constructed using a total of 107 and 144 STS markers covering 12 rice chromosomes in two reciprocal F2 and eight BC1F1 populations, respectively. A total of 15 main-effect QTLs and 17 significant digenic- epistatic interactions controlling spikelet fertility (SF) were resolved in the the entire genome map of F2 BC1F1 populations . Among detected QTLs responsible for hybrid ferility, four QTLs, qSF5.1 and and qS F5.2 on chromosome 5, qSF6.2 on chromosome 6, and qSF12.2 on chromosome 12 were identified as major QTLs since they were located at corresponding position in at least three mapping populations. Loci qSF5.1, qSF6.1 and qSF6.2 were responsible for both female and male sterility, whereas qSF3.1, qSF7 and qSF 12.2 affected the spikelet fertility only through embryosac factors, and qSF9.1 did through pollen factors. Five new QTLs identified in this study will be helpful for understanding the hybrid sterility and for breeding programs via inter-subspecific hybridization.

Hybrid sterility is one of the major barrier to the application of wide crosses in plant breeding and is commonly encountered in crosses between indica and japonica rice varieties. Ten mapping populations comprised of two reciprocal F2 and eight BC1F1 populations generated from the cross between Ilpumbyeo (japonica) and Dasanbyeo (indica) were used to identify QTLs and to interpret the gametophytic factors involved in hybrid fertility or sterility between two subspecies. Frame maps were constructed using a total of 107 and 144 STS markers covering 12 rice chromosomes in two reciprocal F2 and eight BC1F1 populations, respectively. A total of 15 main-effect QTLs and 17 significant digenic- epistatic interactions controlling spikelet fertility (SF) were resolved in the the entire genome map of F2 BC1F1 populations . Among detected QTLs responsible for hybrid ferility, four QTLs, qSF5.1 and and qS F5.2 on chromosome 5, qSF6.2 on chromosome 6, and qSF12.2 on chromosome 12 were identified as major QTLs since they were located at corresponding position in at least three mapping populations. Loci qSF5.1, qSF6.1 and qSF6.2 were responsible for both female and male sterility, whereas qSF3.1, qSF7 and qSF 12.2 affected the spikelet fertility only through embryosac factors, and qSF9.1 did through pollen factors. Five new QTLs identified in this study will be helpful for understanding the hybrid sterility and for breeding programs via inter-subspecific hybridization.

Heterosis describes the increased performance of F1 hybrid plants in terms of increased biomass, yield, vegetative growth rate, and tolerance against biotic and abiotic stresses as compared with their inbred parents. Two sets of rice materials, 166 RILs derived from a cross between Milyang 23 (Korean indica-type rice) and Tong 88-7 (japonica Rice), and BC1F1 hybrids derived from crosses between the RILs and the female parent, Milyang 23, were produced to identify QTLs for heterosis of yield and yield-related traits. The QTLs were detected from three different phenotype data sets including the RILs, BC1F1 hybrids, and mid-parental heterosis data set. A total of 57 QTLs were identified for nine traits. Of eight QTLs detected for yield heterosis, five overlapped with other heterosis QTLs for yield-related traits such as spikelet number per panicle, days to heading, and spikelet fertility. Four QTLs for yield heterosis, gy1.1, py6, gy10, and py11, were newly identified in this study. We identified a total of 17 EpQTLs for yield heterosis that explain 21.4 ~ 59.0 % of total phenotypic variation, indicating that epistatic interactions may play an important role in heterosis.

The HWC-line of rice showed wide compatibility with both indica and japonica cultivars, tall culm length, long and slender grain shape. For QTL analysis, two F2 populations were derived from the crosses between the HWC-line and each of two Korean variety, Dasanbyeo (Korean Tongil-type cultivar) and Hwacheongbyeo (temperate japonica cultivar), respectively. A total of 190 F2 plants were evaluated in each of two F2 populations. Eight agronomic characters were measured for QTL analysis in F2 populations and parents. Two molecular linkage maps were constructed. In the F2 population from cross between HWC-line / Dasanbyeo (HD) cross, 93 STS markers and 13 SSR markers were mapped on 12 chromosomes, covering a total length of 1942.6 cM, with an average distance of 18.33cM between adjacent markers. In the F2 population from HWC-line / Hwacheongbyeo (HH) cross, 28 STS markers, 29 SSR markers and 1 FNP marker were mapped on 11 chromosomes, spanning a total length of 925.53cM, with an average distance of 15.96cM between adjacent markers. In the F2 population from HD cross, 16 M-QTLs and 1 E-QTL were detected for culm length, spikelets per panicle, spikelet fertility, grain length, grain width, grain shape and 100 grains weight. 7 QTLs of spikelet fertility, grain length, grain width and grain shape were newly identified in this study. In the F2 population from HH cross, 15 M-QTLs were detected for culm length, panicle length, spikelet fertility, grain length, grain width, grain shape and 100 grains weight. 6 QTLs of culm length, grain length, grain width and grain shape were newly identified in this study. The QTLs identified in this study would provide basic information on putative functional genes related agronomic characters and facilitate breed new rice cultivar.

In this study, we were conducted the construction of the framework map using SSR markers in the F2 population derived from a cross between waxy corn inbred line (02S6140) and sweet corn inbred line (KSS22), and also identifying of QTLs associated with eating quality traits by employing genetic linkage map of F2:3 population. The linkage map was constructed using 295 SSR markers on the 158 F2 individuals derived from a cross of 02S6140 and KSS22. The map comprised a total genomic length of 2,626.5cM in ten linkage groups and an average distance between markers of 8.9cM. Chi-square test revealed that 254 markers (86.1%) associating with all ten chromosomes exhibited a segregation of 1:2:1 Mendelian ratio. A total of 10 QTLs each for pericarp thickness (PER), amylose content (AMY), dextrose content (DEX), and sucrose content (SUC) were detected in the 158 F2 families. The number of QTL per each trait was ranged from 2 to 4, and also phenotypic variance was ranged from 4.26 to 30.71%. For PER, 4 QTLs were found to be controlled by four genomic regions at locations chromosomes 4, 5, 8, and 9 contributing 10.43, 6.71, 6.74, and 7.79% of phenotypic variance, respectively. While 2 QTLs for AMY, DEX, SUC traits, were found to be controlled by two genomic regions at locations chromosomes 4, 6, 8, and 9 contributing between 4.26 and 30.71% of phenotypic variance, respectively. Among them, 4 QTLs, such as qAMY4 (10.43%), qAMY9 (19.33%), qDEX4 (21.31%), and qSUC4 (30.71%), may be considered as a major QTLs, while the remaining six QTLs might be regarded as minor QTLs. In our study, qAMY9 for amylase content was detected on chromosome 9 in marker intervals phi027-umc1634, which was the same locus as encoding wx1 gene. Thus qAMY9 may be thought very useful molecular marker for selecting amylase content trait. The other QTLs may be thought very useful molecular marker for eating quality traits. The resulting genetic map will be useful in dissection of quantitative traits and the identification of superior QTLs from the waxy hybrid corn, and also this study may provide valuable information for the further identification and characterization of genes responsible for eating quality-related traits in waxy corn and sweet corn.

In order to clarify the chromosomal location of quantitative trait loci (QTL) associated with the yield and agronomic traits in waxy corn and sweet corn (Zea maysL.), we were conducted identifying of QTLs associated with yield and agronomic traits by employing genetic linkage map of F2:3 population. A total of 14 QTLs each for days to silking (DTS), plant height (PH), ear height (EH), ear height ratio (ER), ear length (L-Ear) and kernel setting length (L-Sear) were detected in the 158 F2 families. The number of QTL per each trait was ranged from 1 to 6, and also phenotypic variance was ranged from 3.55 to 16.86%. For DTS, one QTLs was found to be controlled by genomic regions at locations chromosomes 1 contributing 9.21% of phenotypic variance. While three QTLs for PH, were found to be controlled by 3 genomic regions at locations chromosomes 1 and 2 contributing 6.68, 6.85 and 8.17% of phenotypic variance, respectively. For EH, six QTLs were found to be controlled by 6 genomic regions at locations chromosomes 1, 7, 8 and 10 range from 3.55 to 11.44% of phenotypic variance. The one QTLs for ER was found at locations chromosomes 1 contributing 7.25% of phenotypic variance. For L-Ear, two QTLs were found to be controlled by 2 genomic regions at location chromosome 7 and 10 contributing 7.40 and 11.63% of phenotypic variance, respetively. The one QTLs for L-Sear was found at locations chromosomes 3 contributing 16.86% of phenotypic variance. Among them, three QTLs, such as qEH8 (11.44%), qLEar10 (11.63%), and qLSear3 (16.86%) may be considered as a major QTLs, while the remaining 11 QTLs might be regarded as minor QTLs. This study may provide valuable information for the further identification and characterization of genes responsible for agronomic traits in waxy corn and sweet corn.

The earth has been facing a rapid warming during past several decades. To figure out the impact of high temperature on agronomic performance of rice especially on yield, we cultivated 89 rice varieties of various origin in Suwon Korea, Shanghai China and IRRI Philippines(Wet season and Dry season). Days to heading, culm length, panicle length, panicle number, spikelet number, spikelet fertility, grain weight and grain yield were comparatively investigated. Overall grain yield displayed significantly lower values in Shanghai and IRRI(wet and dry) compared with in Suwon. Meanwhile minimum values were much lower in Shanghai and IRRI than in Suwon. However, some varieties such as Keunseom, Taichung178 showed similar performance for grain yield in both Suwon and IRRI(wet season), and some varieties such as Hangangchal, Dasan showed similar performance for grain yield in Suwon, Shanghai and IRRI(wet season), Nampung showed very high yield in Suwon comparing to other two locations. For most varieties, grain yield was the highest in Suwon and followed by in Shanghai and at IRRI(wet season). However, in dry season at IRRI, yield trend was quite different from the expectation. Further studies are in progress to find out the genotype by environment interactions in order to obtain basic information for breeding high temperature tolerant rice.

Two sugary mutants, Hwacheong sugary-1 (Hsu1) and Hwacheong sugary-2 (Hsu2) were obtained by chemical mutagenesis from japonica cultivar, Hwacheongbyeo. Sugary mutants exhibited wrinkled and translucent grain with high soluble sugar content. In addition, amber-colored endosperm of sugary mutants was loosely packed due to abnormal starch granules compared to densely packed wild-type. Especially, the grain of Hsu2 mutant was less wrinkled than that of Hsu1, thus Hsu2 can be polished easily. Previous studies reveal that su1 mutant was resulted from mutation in gene for a debranching enzyme, isoamylase but the sequence of the mutated gene has not been identified. To identify the sequence of sugary genes, the map-based cloning strategy was applied. The genetic study revealed that the phenotype of Hsu2 mutant was controlled by two recessive genes. Interestingly, one of the genes was located on chromosome 8 at the position of isoamylase which was known as su-1. This indicates that mutation in isoamylase gene causes sugary endosperm characteristics. However we found different mutation points between the Hsu1 and Hsu2. The point mutation in Hsu1 was occurred at 10th exon whereas the other mutation related with Hsu2 was occurred at 15th exon. As mentioned above, the Hsu2 mutant has less wrinkled shape and less soluble sugar content than the Hsu1 mutant. Thus, we hypothesize that the other gene controlling Hsu2 mutant phenotype may have a role in weakening the effect of the su-1. Further study on the other gene associated with the Hsu2 phenotype is in progress.