Genotypic differences and inheritance of ozone (O 3 ) resistance in rice were tested in a chamber with an O 3 -producing and monitoring system. Most of the indica cultivars were more resistant than the japonica cultivars based on leaf injury to O 3 . The segregation for O 3 resistance in the F 2 of a cross between resistant and susceptible cultivars revealed a nearly normal distribution. Three significant QTLs associated with O 3 resistance in rice were mapped using the National Institute of Agricultural Science and Technology (NIAST) map and the 164 recombinant inbred lines (MG RILs, F 13 ) derived from Milyang23 (indica/ japonica)/Gihobyeo (japonica). These QTLs conferring O 3 resistance were linked to RZ569A–RG109 on chromosome 1, C507– KCD405 on chromosome 7, and RG119–E13M60.348 on chromosome 11, explaining 20.5% of the total phenotypic variation. The relationship between O 3 resistance and RFLP markers was analyzed in the F 2 populations derived from Milyang 23/ Chucheongbyeo and Milyang 23/Daeribbyeo 1. The RFLP marker RG109 turned out to be polymorphic and significantly distinguished resistance and susceptibility to O 3 of the F 2 populations.

Using a population of recombinant inbred lines of the 164 genotypes derived from a cross between 'Milyang 23' (indica) and 'Gihobyeo' (japonica) in rice (Oryza sativa L.), salt tolerance was evaluated at a young seedling stage in concentrations of 0.5% and 0.7% NaCl. Mapping quantitative trait loci (QTLs) related to salt tolerance was carried out by interval mapping using Qgene 3.0. Two QTLs (qST1 and qST3) conferring salt tolerance at young seedling stage were mapped on chromosome 1 and 3, respectively, and explained 35.5-36.9% of the total phenotypic variation in 0.5% and 0.7% NaCl. The favourable allele of qST1 was contributed by 'Gihobyeo', and that of qST3 by 'Milyang 23'. The results obtained in 0.5% and 0.7% NaCl for 2 years were similar in flanked markers and phenotypic variation.

We describe a rapid and simple procedure for homogenizing leaf samples suitable for mini/midi-scale DNA preparation in rice. The methods used tungsten carbide beads and general vortexer for homogenizing leaf samples. In general, two samples can be ground completely within 11.3+/-1.5 sec at one time. Up to 20 samples can be ground at a time using a vortexer attachment. The yields of the DNA ranged from 2.2 to 7.6 microg from 25-150 mg of young fresh leaf tissue. The quality and quantity of DNA was compatible for most of PCR work and RFLP analysis.

Rapid, large-scale generation of a Ds transposant population was achieved using a regeneration procedure involving tissue culture of seed-derived calli carrying Ac and inactive Ds elements. In the F(2) progeny from genetic crosses between the same Ds and Ac starter lines, most of the crosses produced an independent germinal transposition frequency of 10-20%. Also, many Ds elements underwent immobilization even though Ac was expressed. By comparison, in a callus-derived regenerated population, over 70% of plants carried independent Ds insertions, indicating transposition early in callus formation. In the remaining population, the majority of plants carried only Ac. Most of the new Ds insertions were stably transmitted to a subsequent generation. An exceptionally high proportion of independent transposants in the regenerated population means that selection markers for transposed Ds and continual monitoring of Ac/Ds activities may not necessarily be required. By analyzing 1297 Ds-flanking DNA sequences, a genetic map of 1072 Ds insertion sites was developed. The map showed that Ds elements were transposed onto all of the rice chromosomes, with preference not only near donor sites (36%) but also on certain physically unlinked arms. Populations from both genetic crossing and tissue culture showed the same distribution patterns of Ds insertion sites. The information of these mapped Ds insertion sites was deposited in GenBank. Among them, 55% of Ds elements were on predicted open-reading frame (ORF) regions. Thus, we propose an optimal strategy for the rapid generation of a large population of Ds transposants in rice.

A cDNA library was constructed using mRNA extracted from rice leaves infected with Xanthomonas oryzae pv. oryzae (Xoo), a bacterial leaf blight pathogen, to isolate rice genes induced by Xoo infection. Subtractive hybridization and differential screening of the cDNA library led to the isolation of many induced genes including a nucleotide diphosphate kinase 1 (OsNDPK1) and a pathogenesis-related protein 1 (OsPR1) cDNA. Nucleoside diphosphate kinases (NDPKs) are key metabolic enzymes that maintain the balance between cellular ATP and other nucleoside triphosphates (NTPs). Three other OsNDPK genes (NP922751, OsNDPK2 and OsNDPK3) found in databases were obtained by RT-PCR. Three different programs for predicting subcellular targeting indicated that OsNDPK1 and NP922751 were non-organellar, OsNDPK2 plastidic, and OsNDPK3 mitochondrial. Only transcripts of OsNDPK1 accumulated strongly after infection with Xoo. When rice plants were infected with Burkholderia glumae, a bacterial grain/seedling rot pathogen, the pattern of expression of the rice NDPK genes was similar to that following infection with Xoo. OsNDPK1 gene expression was also strongly induced in response to exposure to salicylic acid, jasmonic acid, and abscisic acid, although the level of transcripts and their pattern of expression depended on the inducer.

The resistance of rice to ozone (O3) is a quantitative trait controlled by nuclear genes. The identification of quantitative trait loci (QTL) and analysis of molecular markers of O3 resistance is important for increasing the resistance of rice to O3 stress. QTL associated with the O3 resistance of rice were mapped on chromosomes 1, 7 and 11 using 164 recombinant inbred (RI) lines from a cross between 'Milyang 23' and 'Gihobyeo'. The quantitative trait loci were tightly linked to the markers RG109, C507 and RG1094 and were detected in each of three replications. The association between these markers and O3 resistance in 26 rice cultivars and doubled haploid (DH) populations was analysed. The markers permit the screening of rice germplasm for O3 resistance and the introduction of resistance into elite lines in breeding programs.

Twenty primers of 20 mer referred to universal rice primer (URP) were developed from a repetitive sequence of rice genome. URP-PCR protocol employed stringent PCR with high annealing temperature throughout the thermo-cycling reaction, giving high reproducibility. Under the PCR condition, each single URP primer produced characteristic fingerprints from diverse genomes containing 14 plants, 7 animals and 6 microbes, indicating its universal applicability. The generality of URP-PCR was demonstrated by applying it to 15 cultivars from five rice species, 23 isolates in four Alternaria species producing host-specific toxins on different host plants and 12 bacterial strains including Escherichia coli, Salmonella spp., and Blucella abortus. PCR approach using URP primers will be useful for studying DNA diversity of most eukaryotic or prokaryotic genomes, especially at inter- and intraspecies levels.

Anther culturability of rice is a quantitative trait controlled by nuclear-encoded genes. The identification of quantitative trait loci (QTL) and associated marker selection for anther culturability is important For increasing the efficiency of green plant regeneration from microspores. QTL associated with the capacity for green plant regeneration in anther culture of rice were mapped on chromosomes 3 and 10 using 164 recombinant inbred (RI) lines from a cross between 'Milyang 23' and 'Gihobyeo'. The quantitative trait locus located on chromosome 10 was detected repeatedly when three anther culture methods were applied and was tightly linked to the markers, RG323, RG241 and RZ400, Associations between these markers and the efficacy of green plant regeneration in 43 rice cultivars and two F-2 populations, 'MG RI036'/'Milyang 23', and 'MG RI036'/'IR 36' were analysed. One of these markers, RZ400, was able to identify effectively genotypes with good (> 10.0%) and poor (< 3.0%) regenerability, based on the marker genotypes in the cultivars and two F, populations. This marker enables the screening of rice germplasm for anther culturability and introgression into elite lines in breeding programmes.

Many aspects of epigenetic phenomena have been elucidated via studies of transposable elements. An active transposable element frequently loses its ability to mobilize and goes into an inactive state during development. In this study, we describe the cyclic activity of a maize transposable element dissociation (Ds) in rice. In rice genome, Ds undergoes the spontaneous loss of mobility. However, an inactive state of Ds can be changed into an active state during tissue culture. The recovery of mobility accompanies not only changes in the methylation patterns of the terminal region of Ds, but also alteration in the steady state level of the activator (Ac) mRNA that is expressed by a constitutive CaMV 35S promoter. Furthermore, the Ds-reactivation process is not random, but stage-specific during plantlet regeneration. Our findings have expanded previous observations on Ac reactivation in the tissue culture of maize.

A marker-assisted selection (MAS) breeding program was used to improve the plant regenerability of indica rice. A significant quantitative trait loci (QTL) that is associated with the capacity for green plant regeneration in the anther culture of rice was mapped on chromosome 10 using recombinant inbred (RI) population from Milyang 23/Gihobyeo. The marker that was chosen to follow the QTL region was used in MAS. This marker co-segregated with the regeneration ability in F2 individuals that were derived from MGRI 079/IR 36. In order to clarify the relationship between this marker and plant regenerability, the backcross population was screened with a RFLP marker. The capacity of plant regeneration of the backcross population was clearly distinguished by the marker genotype. The development of near isogenic line (NILs) with high regenerability through MAS will save time, labor, and cost in indica rice breeding.

PCR-fingerprinting analysis was applied to classify and identify twenty-five pear cultivars from throughout South Korea. Among 12 primers (21mer) used for this experiment, only 10 primers revealed clear and reproducible band patterns, and produced 36 polymorphic bands among 97 bands. Based on the presence of polymorphic bands, the value of the co-phenetic correlation coefficient, a measure of the goodness of fit between the dendrogram and the original similarity matrix, was 0.20. The cultivars were classified by UPGAM clustering method into four main groups. The first group included five cultivars ('Ohsaeshipsegi', 'Singo', 'Shinhong', 'Shinil', 'Jangshimnang'). 'Hangsu', Josangiuk', Wonhwang', 'Kamchonbea', 'Mihwang' and Youngsanbea belonged to the second cluster. The third group had ten cultivars ('Chisung', 'Eshipsegi', 'Hwangkmbea', 'Sunhwang', Hwasan', 'Kamro', 'Mansu', 'Chungsilri', 'Mansamkil' and 'Sinsu'). 'Pungsu', 'Kumchunchu' and 'Kunjongchonsang' belonged to the fourth cluster. From these results, we concluded that there was no correspondence between fruit morphological characteristic and their genetic fingerprint. By contrast the local varieties, allied varieties by the similarity coefficient, were closely related to the distributed areas.

Quantitative trait loci (QTLs), which are associated with the ability of plant regeneration from seed derived calli, were detected using a recombinant inbred (RI) population from a cross between 'Milyang 23 (toingil)' and 'Gihobyeo (japonica)' in rice (Oryza sativa L.). A tongil type cultivar, 'Milyang 23', has a lower frequency of callus induction and plant regeneration than those of japonica 'Gihobyeo'. Transgressive segregations were observed for the callus induction rate and plant regeneration ability from seed derived calli of the RI population. An interval mapping analysis was used to identify the QTL controlling the plant regeneration ability. Two QTLs for the callus induction rate were detected on chromosomes 1 and 2, explaining the 10.9% total phenotypic variation. Four QTLs that are associated with the plant regeneration ability were located on chromosomes 2, 3, and 11, accounting for 25.7% of the total phenotypic variation.

Quantitative trait loci (QTL), associated with the ability of plant regeneration from seed-derived callus of rice, were mapped using a recombinant inbred (RI) population from Milyang 23/Gihobyeo. Each flanking marker, RZ474 and RZ575, tightly linked to two QTLs (qSGR-3-1 and qSGR-3-2) that are located on chromosome 3 was used in marker-assisted selection (MAS). These markers were tested on IR 36/MG RI036 (F3), Milyang 23/MG RI036 (F3), and forty-one rice cultivars. A restriction fragment length polymorphism (RFLP) marker, RZ575, that is located on chromosome 3 could effectively differentiate lines with high and poor regeneration ability, based on marker genotypes. This marker might be applicable for screening rice germplasms with high regeneration ability. Its introgression into elite lines might also be valuable in breeding programs to develop highly responsive genotypes to tissue culture.

Non-redundant expressed sequence tags (ESTs) were generated from six different organs at various developmental stages of Chinese cabbage, Brassica rapa L. ssp. pekinensis. Of the 1,295 ESTs, 915 (71%) showed significantly high homology in nucleotide or deduced amino acid sequences with other sequences deposited in databases, while 380 did not show similarity to any sequences. Briefly, 598 ESTs matched with proteins of identified biological function, 177 with hypothetical proteins or non-annotated Arabidopsis genome sequences, and 140 with other ESTs. About 82% of the top-scored matching sequences were from Arabidopsis or Brassica, but overall 558 (43%) ESTs matched with Arabidopsis ESTs at the nucleotide sequence level. This observation strongly supports the idea that gene-expression profiles of Chinese cabbage differ from that of Arabidopsis, despite their genome structures being similar to each other. Moreover, sequence analyses of 21 Brassica ESTs revealed that their primary structure is different from those of corresponding annotated sequences of Arabidopsis genes. Our data suggest that direct prediction of Brassica gene expression pattern based on the information from Arabidopsis genome research has some limitations. Thus, information obtained from the Brassica EST study is useful not only for understanding of unique developmental processes of the plant, but also for the study of Arabidopsis genome structure.

Two cDNA clones, pOS-ACO2 and pOS-ACO3, encoding 1-aminocyclopropane-1-carboxylate (ACC) oxidase were isolated from rice seedling cDNA library. pOS-ACO3 is a 1,299 bp full-length clone encoding 321 amino acids (Mr=35.9 kDa), while pOS-ACO2 is 1,072 bp long and is a partial cDNA clone encoding 314 amino acids. These two deduced amino acid sequences share 70% identity, and display a high degree of sequence identity (72-92%) with previously isolated pOS-ACO1 of deepwater rice. The chromosomal location studies show that OS-ACO2 is positioned on the long arm of chromosome 9, while OS-ACO3 on the long arm of chromosome 2 of rice genome. A marked increase in the level of OS-ACO2 transcript was observed in IAA-treated etiolated rice seedlings, whereas the OS-ACO3 mRNA was greatly accumulated by ethylene treatment. Results of ethylene inhibitor studies indicated that auxin promotion of the OS-ACO2 transcription was not mediated through the action of auxin-induced ethylene. Thus, it appears that there are two groups of ACC oxidase transcripts in rice plants, either auxin-induced or ethylene-induced. The auxin-induced OS-ACO2 expression was partially inhibited by ethylene, while ethylene induction of OS-ACO3 transcription was completely blocked by auxin. These results indicate that the expression of ACC oxidase genes is regulated by complex hormonal networks in a gene specific manner in rice seedlings. Okadaic acid, a potent inhibitor of protein phosphatase, effectively suppressed the IAA induction of OS-ACO2 expression, suggesting that protein dephosphorylation plays a role in the induction of ACC oxidase by auxin. A scheme of the multiple regulatory pathways for the expression of ACC oxidase gene family by auxin, ethylene and protein phosphatase is presented.

Differential screening of an Arabidopsis cDNA library constructed from the plant tissues harvested 1 h after wounding resulted in the isolation of wound-inducible cDNA clones (Kim et al., 1994). The cDNA clones could be broadly classified into two groups according to the expression time of their transcripts. Nine clones from the 10 different wound-inducible cDNAs were rapidly induced, reaching a maximum level in approximately 1-1.5 h and then were progressively reduced after wounding. The cDNA clone AWI 31 showed steady accumulation of the transcripts and reached the maximum value at a later time point of 2.5 h and then started to decline. The corresponding gene of the AWI 31 in which the coding region was interrupted by an intron, had an open reading frame that predicted a protein of 386 amino acids. However, the gene product did not show any significant homology to other known proteins in the database. Northern hybridization study using the cDNA probe revealed that the gene was not regulated by other environmental stresses such as drought, high salt, low temperature, or a DPE herbicide treatment, indicating that the cDNA clone AWI 31 was specifically induced by wounding.

A wound-inducible cDNA clone (AW? 34) was obtained from the cDNA library of Arabidopsis thaliana by differential screening, The corresponding gene expression was induced rapidly reaching a maximum level in approximately 1.5 h and then progressively reducing after wounding, The predicted amino acid sequence of AWI 34 has 57% homology with the DC 1.2 gene product, The DC 1.2 product is known to be temporarily induced during the initiation of somatic embryogenesis in carrot cells cultured in an auxin(2,4-D)-free medium, The AWI 34 gene was induced by an exogenous 2,4-D treatment on normal plant tissue, The AWI 34 gene was also induced by other environmental stresses such as drought, high-salt, and low-temperature conditions.