Young-Il Cho

Development of a microsatellite framework map providing genome-wide coverage in rice ( Oryza sativa L.)

Abstract Ninety-four newly developed microsatellite markers were integrated into existing RFLP framework maps of four rice populations, including two doubled haploid, a recombinant inbred, and an interspecific backcross population. These simple sequence repeats (SSR) were predominantly poly(GA) motifs, targetted because of their abundance in rice. They were isolated from a previously described sheared library and a newly constructed enzyme-digested library. Differences in the average length of poly(GA) tracts were observed for clones isolated from the two libraries. The length of GA motifs averaged 21 repeat units for clones isolated from the Tsp-509-digested library, while motifs averaged 17 units for clones from the sheared library. There was no evidence of clustering of microsatellite markers near centromeres or telomeres. Mapping of the 94 newly developed markers as well as of 27 previously reported microsatellites provided genome-wide coverage of the 12 chromosomes, with an average distance of 1 SSLP (simple sequence repeat polymorphism) per 16–20 cM.

Characterization and Mapping of a Shattering Mutant in Rice That Corresponds to a Block of Domestication Genes

Easy shattering reduces yield due to grain loss during harvest in cereals. Shattering is also a hindrance in breeding programs that use wild accessions because the shattering habit is often linked to desirable traits. We characterized a shattering mutant line of rice, Hsh, which was derived from a nonshattering japonica variety, Hwacheong, by N-methyl-N-nitrosourea (MNU) treatment. The breaking tensile strength (BTS) of the grain pedicel was measured using a digital force gauge to evaluate the degree of shattering of rice varieties at 5, 10, 15, 20, 25, 30, 35, and 40 days after heading (DAH). The BTS of Hwacheong did not decrease with increasing DAH, maintaining a level of 180–240 gf, while that of Hsh decreased greatly during 10–20 DAH and finally stabilized at 50 gf. Optical microscopy revealed that Hsh had a well-developed abscission layer similar to the wild rice Oryza nivara (accession IRGC105706), while Hwacheong did not produce an abscission layer, indicating that the shattering of Hsh was caused by differentiation of the abscission layer. On the basis of the BTS value and morphology of the abscission layer of F1 plants and segregation data in F2 populations, it was concluded that the easy shattering of Hsh was controlled by the single recessive gene sh-h. The gene sh-h was determined to be located on rice chromosome 7 by bulked segregant analysis. Using 14 SSR markers on rice chromosome 7, the gene sh-h was mapped between the flanking markers RM8262 and RM7161 at distances of 1.6 and 2.0 cM, respectively. An SSR marker Rc17 cosegregated with the gene sh-h. The locus sh-h for shattering was tightly linked to the Rc locus conferring red pericarp, as well as a QTL qSDs-7-1 for seed dormancy, implying that this region might represent a domestication block in the evolutionary pathway of rice.

Discovery of single nucleotide polymorphisms in soybean using primers designed from ESTs

Discovery of single nucleotide polymorphisms (SNPs), including small insertions and deletions (indels), is one of the hot topics in genetic research. SNPs were surveyed using nine soybean genotypes from Korea. Sequence variations in a total of 110 genes from GenBank among the nine genotypes were studied using genomic DNA as a template. Direct fluorescent dideoxynucleotide sequencing data of PCR products from primers designed from soybean ESTs were analyzed by SeqScape software to ensure high accuracy. Approximately 70% of the primer sets produced a single PCR product from which reliable sequence data were obtained, and 23.6% of these had at least one SNP. Overall, a total of 110 ESTs for SNPs were screened in 33,262 bp, consisting of 16,302 bp from coding regions and 16,960 bp from adjacent non-coding regions (5′ UTR, 3′ UTR and introns). SNPs in coding and non-coding regions occurred at a frequency of 1 per 3,260 bp, corresponding to a nucleotide diversity (θ) of 0.00011, and 1 per 278 bp (θ = 0.00128), respectively. This suggested that the higher level of sequence variation in non-coding regions would make them good regions in which to search for SNPs. The SNPs in partial cDNA sequences could be valuable for gene-targeted map construction in soybean.

Shotgun proteomic analysis for detecting differentially expressed proteins in the reduced culm number rice

To survey protein expression patterns in the reduced culm number (RCN) rice, a comparative shotgun proteomic analysis was conducted. For large‐scale protein identification, multidimensional protein identification technology (MudPIT) coupled with pre‐fractionation of plant shoot proteins led to the identification of 3004 non‐redundant rice proteins. By statistically comparing relative amounts of 1353 reproducibly identified proteins between the RCN rice and the wild‐type rice, 44 differentially expressed proteins were detected, where 42 proteins were increased and 2 proteins were decreased in the RCN rice. These proteins appear to have roles in glycolysis, trichloroacetic acid cycle, secondary metabolism, nutrient recycling, and nucleotide metabolism and repair. Consequently, we hypothesized that the RCN rice might fail to maintain sugar nutrient homeostasis. This was confirmed with the observation that the sucrose concentration was increased significantly in the RCN rice compared with the wild‐type rice. Also, the RCN rice showed a hypersensitive response to exogenous sucrose treatment.

Identification of QTLs for hybrid fertility in inter-subspecific crosses of rice (Oryza sativa L.)

Two subspecies in rice, japonica and indica, have their own ecotypic traits. However, reproductive barriers such as spikelet sterility in hybrid progenies between subspecies have been an obstacle in breeding programs for combining desirable traits from both subspecies through inter-subspecific hybridization. The 166 F9 RILs and two BC1F1s’ were analyzed for spikelet and pollen fertility with the parents and F1 between Dasanbyeo (DS, indica) / TR22183 (TR, japonica). A frame map was constructed using a total of 218 polymorphic STS and SSR markers. In both BC1F1s’ of DS//DS/TR and TR//DS/TR, clusters of significant QTLs for spikelet and pollen fertility were identified on the short arm of chromosome 5 and chromosome 8. Nine and ten digenic epistatic interactions for DS//DS/TR and TR//DS//TR were identified, respectively. HF-QTLs were detected at the similar position with subspecies-specific markers and segregation distortion loci, implying that HF-QTLs might be associated with the differentiation of indica and japonica. Hybrid fertility/sterility and its relationship with other traits are discussed in relation to the reproductive barriers between subspecies of rice.