Detection of Drought-Related Loci in Rice at Reproductive Stage Using Selected Introgressed Lines

The present study was carried out to illustrate high-efficient detection of quantitative trait loci （QTLs） with selected introgression lines （ILs） and the existence of ＇hidden genes＇ conferring drought tolerance （DT）. 52 selected DT ILs, derived from BC2Fz population developed by crossing and backcrossing the susceptible recurrent parent （RP） IR64 with the susceptible donor Khazar were planted under irrigation and drought condition. Four important agronomic traits, e.g., grain yield （GY）, heading date （HD）, panicle numbers per plant （PN）, and plant height （PH） were evaluated and 83 SSR polymorphic molecular markers were used for genotypic analysis. Chi-square test based on genetic hitch-hiking and one-way analysis of variances （ANOVA） were used to detect drought-related loci. Nine and 36 loci were detected by chi-square test and one-way ANOVA, respectively. Five common loci were observed by comparing the results of the two methods, among which two QTLs linked with RM7, and RM241 were detected under irrigation condition, both of the favorable alleles were from RP and explained 13% phenotypic variation （PV） for GY and 28% PV for PH, respectively. The other three QTLs linked with RM 163, RM 18, and RM270 were detected under drought condition, the favorable alleles were all from the donor and explained 10, 24, and 19% PV for HD, PH, and PH, respectively. Five common loci were observed by comparing the results of chi-square test and one-way ANOVA including two QTLs （one for GY and one for PH） under irrigation condition and three QTLs （one for HD and two for PH） under drought condition. By combining phenotypic and genotypic analysis, drought escape could be inferred as the main mechanism for drought tolerance in the present study. The results in present study suggested that the selected ILs population analyzed by chi-square test and one-way ANOVA was quite effective for DT QTL detection with low inputs and could also produce useful materials for breeding with wide genetic diversity for drought tolerance.

Identification and validation of root-specific promoters in rice

Novel promoters that confer root-specific expression would be useful for engineering resistance against problems of nutrient and water absorption by roots. In this study, the reverse transcriptase polymerase chain reaction was used to identify seven genes with root-specific expression in rice. The isolation and characterization of upstream promoter regions of five selected genes rice root-specific promoter （rRSP） 1 to 5 （rRSP1-rRSP5） and A2P （the promoter of OsAct2） revealed that rRSP1, rRSP3, and rRSP5 are particularly important with respect to root-specific activities. Furthermore, rRSP1, rRSP3, and rRSP5 were observed to make different contributions to root activities in various species. These three promoters could be used for root-specific enhancement of target gene（s）.

Construction of the Primary Physical Map of Rice Chromosome 12

A primary physical map of rice chromosome 12 was constructed using marker-based chromosome landing and chromosome walking. A BAC library from IR64 was screened using 84 RFLP markers, 4 STS markers and 6 microsatellite markers on chromosome 12 by colony hybridization and polymerase chain reaction (PCR) amplification. A total of 59 contigs consisting of 419 BAC clones including 5 single-clones were physically aligned on rice chromosome 12 with the largest BAC contig covering 855 kb. The whole physical map had a size of ～16 Mb and covered about 52% of rice chromosome 12. This physical map will be certainly helpful for map-based gene cloning of agronomically and biological important genes and understanding the genome structure of the chromosome.