Sesame is queen of oil seed crops and widely cultivated in Asia and Africa. The aim of this study was to develop a mini sub core set representing the diverse germplasm of sesame and to assess the genetic diversity, population structure and phylogenetic relationship of the resulted sub core set to be used in whole genome resequencing platform. One hundred twelve accessions out of 277 accessions were selected by the PowerCore program. A total of 155 alleles were captured from the 158 alleles detected in the primary core population, and rare alleles and specific alleles were also maintained in the sub core set accessions representing almost 100% of the primary core population. Among the sub core set accessions, four sub populations were observed with some admixture accessions. Although the genetic diversity of Pop-1 which includes most accessions from Korea is relatively lower than that of other three sub populations, it can maintain maximum number of accessions in the sub core set with the same percentage as in the primary core set probably because of the specific features of these accessions. Based on this framework of genetically defined populations, the effective use and conservation management of Sesamum indicum for crop improvement might be possible.

Magnesium is important not only for the growth of rice itself, but also as an essential micronutrient component of half of the world population who are supported by rice. Here, we performed genome-wide association study (GWAS) with high-resolution density SNPs to identify natural allelic variation in Mg2+ increase from rice set, which is derived from a total 24,368 rice germplasms. The range of the concentration and distribution of Mg2+ in 295 core accessions of brown rice grain were wide, from 18.17mg/L to 57.11mg/L, with mean 39.71mg/L. In particular, GWAS result shows that the high peak found on chromosomes 3 and 11. The new natural variants identified through haplotyping analysis would be useful to develop new rice varieties with improved storage ability of the valuable mineral through the future molecular breeding.

Objective of this study was to investigate the difference of cadmium (Cd) levels in rice grains from non-polluted fields and to define the gene associated with Cd uptake for producing safety food. Cd was analyzed by Inductively Coupled Plasma Mass Spectrometer (ICP-MS). The average concentration of Cd in rice grains was 0.943 μg/kg and Cd levels ranged from 0.050 to 5.699 μg/kg. Genome-Wide Association study (GWAS) based on phenotype data for Cd levels was performed. However, results of GWAS were affected by subpopulation structure and caused false positive. Therefore, GWAS for rice ecotypes (temperate Japonica, tropical Japonica, Indica, Aus, Aromatic, and Admixture) was performed to minimize false positive. GWAS results showed that Os01g0611300, Os01g0611900, Os01g0611950, Os01g0612000, Os01g0612200, Os11g0444400, Os11g0444700, Os11g0444800, and Os11g0444900 genes have significant correlation with Cd levels in rice grains. The sequences of these genes were compared to sequence positions of each other gene (haplotype analysis). According to the results of haplotype analysis, Cd levels of non-synonymous group were higher than other groups and sequence of non-synonymous group was similar to that of Indica. These results were corresponding to the previous research result that Cd levels of Indica were higher than Japonica. Therefore, candidate genes detected through GWAS need to be examined by knock-out or cross breeding.

Rice (Oryza sativa L.) is one of the most important staple crops in the world, providing main energy source for more than half of the world’s population. It is even closely associated with economic and political stability in many developing countries of Asia and Africa. These days, moreover, amount of land suitable for the agriculture is shrinking due to a variety factors, such as rapid climate changes and industrializations, while rice eating human populations keeps growing. To meet the nutritional and socio-economic demands worldwide, dedicated efforts in developing superior rice varieties need to be reinforced, accumulating and combining beneficial alleles as much as possible from rice germplams. Here, we propose a pipeline for genome assisted breeding where new genomic technologies including GWAS, omics and evolutionary studies together with follow-up breeding programs are integrated. Once pinpointing candidates genes, the integrated genomics approach allows informed choice of parents for the following breeding program based on the haplotype information, in addition to providing precise molecular marker information. We also conducted proof-of-concept analysis, using various agriculturally important phenotypes for rice improvements.

Salt is the major factor limiting crop productivity in saline soils. Development of genetic basis of high salt-tolerant rice is necessary to satisfy urgent needs in rice breeding. In this study, 295 rice accessions from a Korean authentic core set were used to identify the evolution associated genes regarding salt tolerance. By using McDonald-Kreitman Test (MKT), we detected orthologous genes in rice (Oryza sativa) using Brachypodium as an outgroup to investigate fast evolved genes that express differentially based on distinct phenotypic groups. Three groups which represented the salt sensitive (group 1), salt medium tolerant (group 2) and salt tolerant (group 3) were separated and each group was examined with the outgroup in neutral and non-neutral polymorphism together with the divergence levels. Total 53 fast evolutionary genes that have a positive selection with FDR ≤ 0.05 were found in the three groups. Among them, 15, 31 and 7 genes were included exclusively in group 1, 2 and 3, respectively. Annotation of these genes showing the predicted functions were checked. Two genes were found to be related to high salt tolerance based on the previous studies. Besides, association study of the candidate gene alleles and salt tolerance phenotype was carried out, indicating that these genes were correlated with salt tolerance. All these result support that using this type of evolution study, we may find some important candidate genes which are related to important traits in rice, such as the salt tolerance, providing important information for future gene based molecular breeding and functional analysis in rice.

In rice (Oryza sativa L.), there is a diversity in flowering time that is strictly genetically regulated by plenty of genes. The floral transition from vegetative to reproductive development is a very important step in the life cycle of a flowering plant. Orthologous genes, which are homologous genes that diverged after a speciation event, generally maintain a similar function in different species. with a McDonald-Kreitman Test (MKT), we examined more than 10,000 orthologous genes between rice (Oryza sativa) and Brachypodium (outgroup), based on different phenotypic groups, to find some fast evolutionary genes of rice flowering time. Three groups with early flowering time (group 1), midium flowering time (group 2) and late flowering time (group 3) were separated and each group was examined for McDonald-Kreitman Test (MKT). Total 70 fast evolutionary genes under a positive selection were found in the three groups, and 14, 42 and 14 genes were specific existed in group 1, 2 and 3, respectively. Annotation of these genes were conducted and the predicted functions were also surveyed. In addition, network analysis of these characterized genes were also investigated to infer related pathways. And also, the association study between the one early flowering factor and the flowering time phenotype was performed and indicated that this gene is significantly correlated with flowering time in rice. These results suggest that using this orthologous based method, we could find some important candidate genes underlying flowering time regulations.

Iron is an essential mineral found in every cell of the human body to make the oxygen-carrying proteins hemoglobin and myoglobin. More than 2 billion people face Fe deficiency. Rice can be a potentially valuable source to supplement that mineral since it is staple food for two-thirds of the world’s population. To bring the nutritional level of the milled product up to that of the whole grain (brown), rice should be enriched with thiamin, niacin and iron. Also iron has important role that absorption from the photosynthetic cells proceeds, chlorophyll synthesis and the growth process of the plant. Orthologous genes, which are homologous genes that diverged after a speciation event, generally maintain a similar function in different species. We applied a McDonald-Kreitman Test (MKT) to examine more than 10,000 orthologous genes between rice (Oryza sativa) and Brachypodium (outgroup) based on different phenotypic groups. This analysis was undertaken to find fast evolutionary genes in rice iron uptake. Three groups were separated based on the phenotype and each group was examined with the outgroup for MKT. Fast evolutionary genes that have a positive selection with FDR ≤ 0.05 were detected at each groups. Annotation of these genes were conducted and the predicted functions were also discussed here. And also, the association study between the candidate gene related to iron uptake phenotype was performed. These results support that using this orthologous based method, we may find some important candidate genes underlying the ion uptake in rice.

Although the overall structure of the chloroplast genome is generally conserved, a number of sequence variations have been identified, which are valuable for plant population and evolutionary studies. Here, we constructed a chloroplast variation map of 30 landrace rice strains of Korean origin, using the Oryza rufipogon chloroplast genome (Genbank: NC_017835) as a reference. Differential distribution of single nucleotide polymorphisms (SNPs) and indels across the rice chloroplast genome is suggestive of a region-specific variation. Population structure clustering revealed the existence of two clear subgroups (indica and japonica) and an admixture group (aus). Phylogenetic analysis of the 30 landrace rice strains and six rice chloroplast references suggested and supported independent evolution of O. sativa indica and japonica. Interestingly, two “aus” type accessions, which were thought to be indica type, shared a closer relationship with the japonica type. One hypothesis is that “Korean aus” was intentionally introduced and may have obtained japonica chloroplasts during cultivation. We also calculated the nucleotide diversity of 30 accessions and compared to six rice chloroplast references, which shown a higher diversity in the indica and aus groups than in the japonica group in lower level substitution diversity.

Pre-harvest sprouting (PHS) results in lower yields for rice and other crops, especially in rainy season before harvest. By using gene based functional studies to reveal the mechanism of PHS related pathways can be a good way in breeding for more PHS resistant accessions. Orthologous genes, which are homologous genes that diverged after a speciation event, generally maintain a similar function in different species to that of the ancestral gene in which they evolved from. Applied with a McDonald-Kreitman Test (MKT), we examined more than 10,000 orthologous genes between rice (Oryza sativa) and Brachypodium (outgroup) based on different phenotypic groups in order to find some fast evolutionary genes in rice PHS. Three groups which represented the PHS susceptible (group 1), PHS medium (group 2) and PHS resistant (group 3) were separated based on the phenotype and each group was examined with the outgroup for MKT. Total 60 fast evolutionary genes that have a positive selection with FDR ≤ 0.05 were found in the three groups, and 19, 5 and 8 genes were specific existed in group 1, 2 and 3, respectively. Annotation of these genes were conducted and the predicted functions were investigated, leading that one Ethylene receptor-like gene that may related to PHS based on the previous studies, which need to be validated later, however. In addition, network analysis of these characterized genes were also investigated, which could reveal the connection of genes between each other. Moreover, the association study between the candidate gene ethylene receptor and the PHS phenotype was performed and indicated that this gene is significantly correlated with PHS in rice. All these above indicated that with this orthologous based method, we can find some important candidate genes that may play an important role in some traits.

Ratio of functional changes from orthologous genes is being widely used for detecting the signature for natural selection between species. However, one to one orthologous genes allows only for the analysis due to methodological limitation. A number of genes have in-paralogs as a result of gene expansion in crops. Here, we report a new approach for detecting accelerated evolution, which includes in-paralogs as well as one to one orthologs. This new approach can detect many novel accelerated genes among rice in-paralogs, which have not been investigated yet.

Rice germplasm collections continue to grow in number and size around the world. Since maintaining and screening such massive resources remain as a great challenge, it is important to establish piratical ways to manage them. A core collection, by definition, refers to a subset of entire population but preserves most of the possible genetic diversity, enhancing the efficiency for germplasm utilizations. Here we reports the whole genome resequencing of the 137 Korean rice core set (KRICE_CORE) that represents 25,604 rice germplasms deposited in Korean genebank of Rural Development Administration (RDA). We implemented the Illumna HiSeq 2000 and 2500 platform to produce short reads and then assembled those with 9.8x depth using Nipponbare as a reference. Comparisons of the sequences with the reference genome yield more than 15 million(M) single nucleotide polymorphisms (SNPs) and 1.3M insertion/deletion (INDELs). Phylogenetic and population analyses using 2,046,529 high quality SNPs successfully assigned each rice accessions to the relevant subgroups, suggesting those SNPs comprehensively capture evolutionary signatures accumulated in rice subpopulations. Furthermore, genome-wide association studies (GWAS) for 4 exemplary agronomic traits from the KRIC_CORE manifest the utility of KRICE_CORE, identifying previously defined gene or novel genetic polymorphisms that potentially regulate the important phenotypes. This study provides strong evidences that the size of KRICE_CORE is small but contains such a high genetic and functional diversity across the genome. Thus those resequencing results will be useful for future breeding, functional and evolutionary studies in the post-genomic era.