Comparative analyses of linkage maps and segregation distortion of two F₂ populations derived from japonica crossed with indica rice

To facilitate genetic research, we constructed two linkage maps by employing two F? populations derived from rice inter-subspecific crosses, japonica Tainung 67 (TNG67)/indica Taichung Sen 10 (TCS10) and japonica TNG67/indica Taichung Sen 17 (TCS17). We established linkage map lengths of 1481.6 cM and 1267.4 cM with average intervals of 13.8 cM and 14.4 cM by using 107 and 88 PCR markers for coverage of 88% of the rice genome in TNG67/TCS10 and TNG67/TCS17, respectively. The discrepancy in genetic maps in the two populations could be due to different cross combinations, crossing-over events, progeny numbers and/or markers. The most plausible explanation was segregation distortion; 18 markers (16.8%) distributed at nine regions of seven chromosomes and 10 markers (11.4%) at four regions of four chromosomes displayed severe segregation distortion (p < 0.01)in TNG67/TCS10 and TNG67/TCS17, respectively. All segregation-distorted markers in these two populations corresponded to reported reproductive barriers, either gametophytic or zygotic genes but not to hybrid breakdown genes. The observed recombination frequency, which was higher or lower than the intrinsic frequency, revealed the association of segregation distortion skewed to the same or different genotypes at the consecutive markers. The segregation distortion, possibly caused by reproductive barriers, affects the evaluation recombination frequencies and consequently the linkage analysis of QTLs and positional cloning.     

Genetic factors responsible for eating and cooking qualities of rice grains in a recombinant inbred population of an inter-subspecific cross

The eating and cooking qualities of rice grains are the major determinants of consumer preference and, consequently, the economic value of a specific rice variety. These two qualities are largely determined by the physicochemical properties of the starch, i.e. the starch composition, of the rice grain. In our study, we determined the genetic factors responsible for the physicochemical properties of starch in recombinant inbred lines (RILs) of japonica cv. Tainung 78 × indica cv. Taichung Sen 17 (TCS 17) cultivated over two crop seasons by examining palatability characteristics and several Rapid Viscosity Analyzer (RVA) parameters. Thirty-four quantitative trait loci (QTLs), each explaining between 1.2 and 78.1 % phenotypic variation, were mapped in clusters on eight chromosomes in 190 RILs genotyped with 139 markers. Ten pairs of QTLs were detected in the two environments, of which seven were in agreement with previous findings, suggesting that these QTLs may express stable experimental populations across various environments. Waxy (Wx), which controls amylose synthesis, was determined to be a primary gene regulating the physicochemical properties of cooked rice grains, as indicated by the presence of a major QTL cluster on chromosome 6 and by marker regression analysis. Six starch synthesis-related genes (SSRGs) which were located in the QTL intervals significantly differed in terms of gene expression between the two parents during grain-filling and were important genetic factors affecting physicochemical properties. The expression of four genes, PUL, ISA2, GBSSI, and SSII-3, was significantly upregulated in TCS 17, and this expression was positively correlated with six traits. The effects of the six SSRGs and gene interaction depended on genetic background and environment; grain quality may be fine tuned by selecting for SBE4 for japonica and PUL for indica. We provide valuable information for application in the breeding of new rice varieties as daily staple food and for use in industrial manufacturing by marker-assisted selection.     

A high-density genetic recombination map of sequence-tagged sites for sorghum, as a framework for comparative structural and evolutionary genomics of tropical grains and grasses

We report a genetic recombination map for Sorghum of 2512 loci spaced at average 0.4 cM ( approximately 300 kb) intervals based on 2050 RFLP probes, including 865 heterologous probes that foster comparative genomics of Saccharum (sugarcane), Zea (maize), Oryza (rice), Pennisetum (millet, buffelgrass), the Triticeae (wheat, barley, oat, rye), and Arabidopsis. Mapped loci identify 61.5% of the recombination events in this progeny set and reveal strong positive crossover interference acting across intervals of 相似文献   

A Sorghum propinquum BAC library,suitable for cloning genes associated with loss-of-function mutations during crop domestication

A large insert Sorghum propinquum BAC library has been constructed to analyze the physical organization of the sorghum genome and to facilitate positional cloning of sorghum genes and QTLs associated with the early stages of grain crop domestication. This library was established from 12 different ligations using high-molecular-weight DNA generated from either one cycle or two cycles of size selection. This library consists of 38 016 BAC clones with an estimated average insert size of 126 kb and coverage of 6.6 genome equivalents. The 6.6 genome-equivalent BAC library of S. propinquum provides a 99.7% probability of finding one or more BACs that contain genes of interest. Twenty mapped DNA probes, ten homologous and ten heterologous, were used to screen the library, and 121 positive clones were identified, 6.05 per locus or 6.37 per probe.