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.

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.

Rice is the major food for half of the world population. The nutrition component in rice is critical for improvement of people’s health. Vitamin E serves as important antioxidant by quenching the free radical intermediates and thus protects the cell membrane. Because of the high nutritional value and the benefits of vitamin E in human health, increasing the tocochromanol content of major agricultural crops has long been in the focus of breeding programs and genetic engineering approaches. The key genes involved in tocopherol biosynthesis have been elucidated in Arabidopsis and other model organisms. Quantitative trait locus (QTL) study performed in Arabidopsis suggested that some of these key genes and a few additional loci contribute to natural tocopherol variations. Identifying such genetic variations in rice, enrich our understanding of the genetic mechanisms controlling tocopherol variation, which can be directly applied to rice breeding programs. In this study, we used genome-wide association mapping with high-resolution density SNPs of rice core set to identify natural allelic variations, which contribute to tocopherol increase in rice

Chloroplast (cp) DNA sequence data are a versatile tool for plant identification, barcoding and establishing genetic relationships among plant species. Different chloroplast loci have been utilized to infer evolutionary relationship of plant species. Although the overall structure of the chloroplast genome is generally well conserved, a number of mutations have been observed. Thus, documentation of chloroplast sequence variation has also been an valuable asset in plant population and evolutionary studies for over two decades. Recently, advance in chloroplast genome assembly from whole genome NGS data has become available. In the present study, chloroplast variations among 295 diverse origin accessions were detected based on Oryza rufipogon, which thought to be the progenitor of cultivated rice.. Variation calling was carried out using the whole genome re-sequencing data of those accessions along with the five rice reference cp genomes. Phylogenetic and evolution analysis of the six references and 295 accessions were performed using the whole reference genome sequence and the variation data, respectively. Also, nucleotide polymorphisms of 295 rice accessions were validated by using previously characterized 50 ecotypes. Differential SNP frequency across the rice cp genome suggests a regional dependent preferential high variation occurrence during the evolution of chloroplast

As one of the most important crop, rice is not only a staple food of half world’s population but a wonderful model plant, which has been leading the evolution and functional genomics study. The next-generation sequencing technology are expediting rice genomic study, by providing a simple but powerful way. In this study, we re-sequenced a core collection of 137 rice accessions from all over the world along with 158 Korean breeding varieties. Finally, 6.3G uniquely mapped reads were obtained, and about 10 million SNPs and ~1.2 million InDels were identified with average sequencing depth of 7.5X. These will help us to maximize our germplasm utilization and assists all the deep research in population dynamics and functional studies. Here, we’d like to show the approaches applied to resequencing data mining and on-going activities.