Indica is not only an important rice subspecies widely planted in Asia and the rest of the world,but it is also the genetic background of the majority of hybrid varieties in China.Studies on genetic structure and genetic diversity in indica germplasm resources are important for the classification and utilization of cultivated rice in China.Using a genetically representative core collection comprising 1482 Chinese indica landraces,we analysed the genetic structure,geographic differentiation and diversity.Model-based structure analysis of varieties within three ecotypes revealed nine eco-geographical types partially accordant with certain ecological zones in China.Differentiation of eco-geographical types was attributed to local ecological adaption and physical isolation.These groups may be useful for developing heterotic groups of indica.To facilitate the identification of different ecotypes and eco-geographical types,we identified characteristic SSR alleles of each ecotype and eco-geographical type and a rapid index of discrimination based on characteristic alleles.The characteristic alleles and rapid discrimination index may guide development of heterotic groups,and selection of hybrid parents.
Awnness is a key trait in rice domestication, yet no studies have been conducted on fine mapping or association mapping of the rice awn gene. In this study, we investigated the awnness and genotype of a core collection of 303 cultivated rice varieties and a BC5F2 segregating population of 200 individuals. Combining association and linkage analyses, we mapped the awnness related genes to chromosome 4. Primary association analysis using 24 SSR markers revealed five loci significantly associated with awnness on chromosome 4. The associated markers cover previously identified regions. Fine association mapping was conducted using another 29 markers within a 4-Mb region, covering the associated marker in34, which is close to the awn gene Awn4.1. Seven associated markers were revealed, distributed over an 870-kb region. Combining the fine association mapping and linkage analysis of awnness in the 200 BC5F2 segregating population, we finally identified a 330-kb region as the candidate region for Awn4.1. The results indicate that combining association mapping and linkage mapping provides an efficient and precise approach to both genome-wide mapping and fine mapping of rice genes.
China is one of the largest centers of genetic diversity of Oryza sativa L. and is the original centers of Oryza sativa L. subspecies japonica. Using a genetically representative core collection of 1 442 rice landraces of japonica in China, the genetic structure, differentiation, and geographic diversity were analyzed. The model-based structure analysis on varieties within three ecotypes revealed 16 eco-geographical types, which are partially accorded with some of the ecological zones in China. The differentiation of eco-geographical types contributed to the local ecological adaption and physical isolation, and maybe could be used to develop the heterotic groups of japonica. To facilitate the identification of different ecotypes and eco-geographical types, we provided the SSR character alleles of each ecotype or geographical eco-group and a rapid discriminated method based on these character alleles. Lastly, investigation on genetic diversity, genetic differentiation indicated that southwest region of China, including south of Yunnan Province, northwest of Guangxi Zhuang Autonomous Region, and southwest of Guizhou Province, possessed the highest genetic diversity and all the necessary conditions as a center of genetic diversity and should be the center of genetic diversity of rice landraces of japonica in China.
Grain number per-panicle is one of the most important components for rice yield. Spikelets on the primary and secondary branches determine the grain number per-panicle in rice. In this study, we identified a natural mutant, gnp4, lack of lateral spikelet on the secondary branches in the field condition. In addition, the Gnp4 and Lax1-1 double mutant showed dramatically reduced secondary branches and spikelets in panicle at reproductive stage, and tillers at vegetative stage. By map-based cloning approach, and using four F2 segregating populations, the Gnp4 gene was finally mapped to a 10.7-kb region on the long arm of chromosome 4 in rice. In this region, only one gene was predicted, and genomic DNA sequencing of the 10.7-kb region showed no nucleotide differences between the mutant and wild type. Interestingly, we found that the methylation level of several cytosines in the promoter CpG islands region of the predicted gene in gnp4 were different from the wild type. Thus, we propose that the DNA methylation changes at these sites may induce to decrease expression level of Gnp4, consequently, resulting in phenotypic variation.
ZHANG Zhan-ying LI Jin-jie YAO Guo-xin ZHANG Hong-liang DOU Hui-jing SHI Hong-li SUN Xing-ming LI Zi-chao
Oryza sativa and Oryza latifolia belong to the AA and CCDD genomes of Oryza, respectively. In this study, amphiploids were obtained from the tube seedlings of O. sativa × O. latifolia F1 hybrids by treatment with colchicine, an agent for chromosome doubling. Subse- quently, amphiploids were investigated using the methods of morphology, genomic in situ hybridization, and molec- ular markers. Amphiploids were characterized by a shorter plant height, larger diameter of stem, longer and wider leaves, darker leaf color, decreased spikelets per panicle and panicle length, and larger spikelets and anthers than the original F1 hybrid. Based on the mitotic metaphase chro- mosome number of the investigated root tips, the somatic chromosome number of the amphiploid is 2n = 72. Additionally, the amphiploid is an allohexaploid, and its genomic constitution is AACCDD by genomic in situ hybridization analysis. Finally, the amphiploids were identified to be true using 37 polymorphic markers at the DNA level.
