[show abstract][hide abstract] ABSTRACT: Crop domestications are long-term selection experiments that have greatly advanced human civilization. The domestication of cultivated rice (Oryza sativa L.) ranks as one of the most important developments in history. However, its origins and domestication processes are controversial and have long been debated. Here we generate genome sequences from 446 geographically diverse accessions of the wild rice species Oryza rufipogon, the immediate ancestral progenitor of cultivated rice, and from 1,083 cultivated indica and japonica varieties to construct a comprehensive map of rice genome variation. In the search for signatures of selection, we identify 55 selective sweeps that have occurred during domestication. In-depth analyses of the domestication sweeps and genome-wide patterns reveal that Oryza sativa japonica rice was first domesticated from a specific population of O. rufipogon around the middle area of the Pearl River in southern China, and that Oryza sativa indica rice was subsequently developed from crosses between japonica rice and local wild rice as the initial cultivars spread into South East and South Asia. The domestication-associated traits are analysed through high-resolution genetic mapping. This study provides an important resource for rice breeding and an effective genomics approach for crop domestication research.
[show abstract][hide abstract] ABSTRACT: A high-density haplotype map recently enabled a genome-wide association study (GWAS) in a population of indica subspecies of Chinese rice landraces. Here we extend this methodology to a larger and more diverse sample of 950 worldwide rice varieties, including the Oryza sativa indica and Oryza sativa japonica subspecies, to perform an additional GWAS. We identified a total of 32 new loci associated with flowering time and with ten grain-related traits, indicating that the larger sample increased the power to detect trait-associated variants using GWAS. To characterize various alleles and complex genetic variation, we developed an analytical framework for haplotype-based de novo assembly of the low-coverage sequencing data in rice. We identified candidate genes for 18 associated loci through detailed annotation. This study shows that the integrated approach of sequence-based GWAS and functional genome annotation has the potential to match complex traits to their causal polymorphisms in rice.
[show abstract][hide abstract] ABSTRACT: The extent of and accessibility to genetic variation in a large germplasm collection are of interest to biologists and breeders. Construction of core collections (CC) is a favored approach to efficient exploration and conservation of novel variation in genetic resources. Using 4,310 Chinese accessions of Oryza sativa L. and 36 SSR markers, we investigated the genetic variation in different sized sub-populations, the factors that affect CC size and different sampling strategies in establishing CC. Our results indicated that a mathematical model could reliably simulate the relationship between genetic variation and population size and thus predict the variation in large germplasm collections using randomly sampled populations of 700-1,500 accessions. We recommend two principles in determining the CC size: (1) compromising between genetic variation and genetic redundancy and (2) retaining the main types of alleles. Based on the most effective scheme selected from 229 sampling schemes, we finally developed a hierarchical CC system, in which different population scales and genetic diversities allow a flexible use of genetic resources. The CC, comprising 1.7% (932) of the accessions in the basic collection, retained more than 85% of both the SSR and phenotypic variations. A mini core collection, comprising 0.3% (189) of the accessions in the basic collection, retained 70.65% of the SSR variation and 76.97% of the phenotypic variation, thus providing a rational framework for intensive surveys of natural variation in complex traits in rice genetic resources and hence utilization of variation in rice breeding.
Theoretical and Applied Genetics 01/2011; 122(1):49-61. · 3.66 Impact Factor
[show abstract][hide abstract] ABSTRACT: Copy number variations (CNVs) can create new genes, change gene dosage, reshape gene structures, and modify elements regulating gene expression. As with all types of genetic variation, CNVs may influence phenotypic variation and gene expression. CNVs are thus considered major sources of genetic variation. Little is known, however, about their contribution to genetic variation in rice.
To detect CNVs, we used a set of NimbleGen whole-genome comparative genomic hybridization arrays containing 718,256 oligonucleotide probes with a median probe spacing of 500 bp. We compiled a high-resolution map of CNVs in the rice genome, showing 641 CNVs between the genomes of the rice cultivars 'Nipponbare' (from O. sativa ssp. japonica) and 'Guang-lu-ai 4' (from O. sativa ssp. indica). The CNVs identified vary in size from 1.1 kb to 180.7 kb, and encompass approximately 7.6 Mb of the rice genome. The largest regions showing copy gain and loss are of 37.4 kb on chromosome 4, and 180.7 kb on chromosome 8. In addition, 85 DNA segments were identified, including some genic sequences. Contracted genes greatly outnumbered duplicated ones. Many of the contracted genes corresponded to either the same genes or genes involved in the same biological processes; this was also the case for genes involved in disease and defense.
We detected CNVs in rice by array-based comparative genomic hybridization. These CNVs contain known genes. Further discussion of CNVs is important, as they are linked to variation among rice varieties, and are likely to contribute to subspecific characteristics.
[show abstract][hide abstract] ABSTRACT: Uncovering the genetic basis of agronomic traits in crop landraces that have adapted to various agro-climatic conditions is important to world food security. Here we have identified ∼ 3.6 million SNPs by sequencing 517 rice landraces and constructed a high-density haplotype map of the rice genome using a novel data-imputation method. We performed genome-wide association studies (GWAS) for 14 agronomic traits in the population of Oryza sativa indica subspecies. The loci identified through GWAS explained ∼ 36% of the phenotypic variance, on average. The peak signals at six loci were tied closely to previously identified genes. This study provides a fundamental resource for rice genetics research and breeding, and demonstrates that an approach integrating second-generation genome sequencing and GWAS can be used as a powerful complementary strategy to classical biparental cross-mapping for dissecting complex traits in rice.
[show abstract][hide abstract] ABSTRACT: With 2 figures and 1 tableAbstractThis study used a double haploid (DH) population of ‘Maybelle’, a USA japonica variety susceptible to sheath blight (ShB), and ‘Baiyeqiu’, a Chinese indica landrace resistant to ShB, to identify quantitative trait loci (QTL) controlling rice ShB resistance. The DH population (251 lines) was inoculated with R. solani strain RH-9. A molecular linkage map saturated with 227 markers was constructed. We detected a total of four QTL located on four different chromosomes (qShB1, qShB2, qShB3 and qShB5). The qShB1 QTL explained 8.9% of the phenotypic variation in 2007 and 13.2% in 2008.
[show abstract][hide abstract] ABSTRACT: China is one of the largest centers of genetic diversity of Oryza sativa L. in the world. Using a genetically representative primary core collection of 3,024 rice landraces in China, we analyzed the genetic structure and intraspecific differentiation of O. sativa, and the directional evolution of SSR. The genetic structure was investigated by model-based structure analysis and construction of neighbor-joining phylogenetic tree. Comparison between genetic structure and predefined populations according to Ting's taxonomic system revealed a hierarchical genetic structure: two distinct subspecies, each with three ecotypes and different numbers of geo-ecogroups within each ecotype. Two subspecies evidently resulted from adaptation to different environments. The different cropping systems imposed on the subspecies led to further differentiation, but the variation within each subspecies resulted from different causes. Indica, under tropical-like or lowland-like environments, exhibited clear differentiation among seasonal ecotypes, but not among soil-watery ecotypes; and japonica showed clear differences between soil water regime ecotypes, but not among seasonal ecotypes. Chinese cultivated rice took on evident directional evolution in microsatellite allele size at several aspects, such as subspecies and geographical populations. Japonica has smaller allele sizes than indica, and this may partly be the result of their different domestication times. Allele size was also negatively correlated with latitude and altitude, and this may be interpreted by different mutation rates, selection pressures, and population size effects under different environments and cropping systems.
Theoretical and Applied Genetics 09/2009; 119(6):1105-17. · 3.66 Impact Factor
[show abstract][hide abstract] ABSTRACT: Forty simple sequence repeats (SSRs) were used to assess the changes of diversity in 310 major Chinese rice cultivars grown during the 1950s-1990s. Of the 40 SSR loci, 39 were polymorphic. A total of 221 alleles were detected with an average of 5.7 alleles per locus (Na). The Nei's genetic diversity index (He) varied drastically among the loci (0.207 to 0.874, mean 0.625). Comparing the temporal changes in Na and He, the cultivars from the 1950s had more alleles and higher He scores than the cultivars from the other four decades. Analysis of molecular variance (AMOVA) indicated that the genetic differentiation among the five decades was not significant in the whole set, but significant within indica and japonica. More changes among the decades were revealed in indica cultivars than in japonica cultivars. Some alleles had been lost in current rice cultivars in the 1990s, occurring more frequently in indica. These results suggest that more elite alien genetic resources should be explored to widen the genetic backgrounds of rice cultivars currently grown in China.
Journal of Genetics and Genomics 07/2009; 36(6):363-70. · 2.08 Impact Factor
[show abstract][hide abstract] ABSTRACT: To study how changes in gene regulation shape phenotypic variations in rice, we performed a comparative analysis of genome expression in the heading-stage panicle from six lineages of cultivated and wild rice, including Oryza sativa subsp. indica, japonica and javanica, O. nivara , O. rufipogon and O. glaberrima. While nearly three-quarters of the genes are expressed at a constant level in all six lineages, a large portion of the genome, ranging from 1767 to 4489 genes, exhibited differential expression between Asian domesticated and wild rice with repression or down-regulation of genome expression in Asian cultivated rice as the dominant trend. Importantly, we found this repression was achieved to a large extent by the differential expression of a single member of paralogous gene families. Functional analysis of the differentially expressed genes revealed that genes related to catabolism are repressed while genes related to anabolism up-regulated. Finally, we observed that distinct evolutionary forces may have acted on gene expression and the coding sequences in the examined rice lineages.
[show abstract][hide abstract] ABSTRACT: Preserving many kinds of rice resources and rich variations, Guizhou Province is one of the districts with the highest genetic
diversity of cultivated rice (Oryza sativa L.) in China. In the current research, genetic diversity and structure of 537 accessions of cultivated rice from Guizhou
were studied using 36 microsatellite markers and 39 phenotypic characters. The results showed that the model-based genetic
structure was the same as genetic-distance-based one using SSRs but somewhat different from the documented classification
(mainly based on phenotype) of two subspecies. The accessions being classified into indica by phenotype but japonica by genetic structure were much more than that being classified into japonica by phenotype but indica by genetic structure. Like Ding Ying’s taxonomic system of cultivated rice, the subspecific differentiation was the most
distinct differentiation within cultivated rice. But the differentiation within indica or japonica population was different: japonica presented clearer differentiation between soil-watery ecotypes than indica, and indica presented clearer differentiation between seasonal ecotypes than japonica. Cultivated rices in Guizhou revealed high genetic diversity at both DNA and phenotypic levels. Possessing the highest genetic
diversity and all the necessary conditions as a center of genetic diversity, region Southwestern of Guizhou was suggested
as the center of genetic diversity of O. sativa L. from Guizhou.
Chinese Science Bulletin 01/2007; 52(3):343-351. · 1.32 Impact Factor
[show abstract][hide abstract] ABSTRACT: To understand geographical distribution of the genetic diversity of rice cultivars (Oryza sativa L.) and its trends in recent fifty years in China, 453 accessions were analyzed by 36 microsatellites loci and 42 phenotypic
traits. Results revealed that the genetic diversity by SSRs is highly consistent with that by phenotypic traits and the genetic
diversity of indica cultivars was higher than that of japonica cultivars; the genetic diversity of cultivars declined from 1950s to 1980s and then increased greatly; among the six rice
ecological zones (REZs), genetic diversity of REZ II was the highest and those of REZ V and REZ VI were the lowest at both
DNA and phenotypic level. Jiangsu and Jiangxi provinces in the middle and lower reaches of Yangtze River and Sichuan province
in southwest of China were the areas with the highest genetic diversity. Breeders in REZ V which is an important japonica rice area but with very low genetic diversity should explore more gene resources to widen the genetic backgrounds of cultivars.
Chinese Science Bulletin 02/2006; 51(6):681-688. · 1.32 Impact Factor
[show abstract][hide abstract] ABSTRACT: In this paper, the effects of transgenes insertion on the outcross potentiality of rice varieties were assessed by pollen vigor and hybrid seed set. The in vitro pollen germination rates of five transgenic rice lines transformed respectively with bar, crylAb, BADH and Xa21 gene were investigated, and compared with their relative receptor rice varieties. The results showed that there existed a significant difference in in vitro pollen germination rates between receptor rice varieties, but no significant difference was found between transgenic rice varieties and their relative receptors. The in vitro pollen germination rate for transgenic rice varieties varied from 0.416 to 0.584, similar to that of their relative receptors (0.400-0.574). Investigation on the hybrid seed set of 26 hand-crosses showed that the inserted bar or crylAb gene had a significant effect on the hybrid seed set of receptors, while the effect of Xa21 gene was smaller. The hybrid seed set rate of non-transgenic rice in crosses with transgenic rice (pollen donor) was from 0.056 to 0.413, not different from that in crosses with their relative receptors (0.052-0.417). It's suggested that transgenes insertion had little effect on the outcross potentiality of rice varieties.
Ying yong sheng tai xue bao = The journal of applied ecology / Zhongguo sheng tai xue xue hui, Zhongguo ke xue yuan Shenyang ying yong sheng tai yan jiu suo zhu ban 02/2005; 16(1):115-8.