Mi-Ok Woo

High-resolution mapping of two rice brown planthopper resistance genes, Bph20(t) and Bph21(t), originating from Oryza minuta

Brown planthopper (BPH) is one of the most destructive insect pests of rice. Wild species of rice are a valuable source of resistance genes for developing resistant cultivars. A molecular marker-based genetic analysis of BPH resistance was conducted using an F2 population derived from a cross between an introgression line, ‘IR71033-121-15’, from Oryza minuta (Accession number 101141) and a susceptible Korean japonica variety, ‘Junambyeo’. Resistance to BPH (biotype 1) was evaluated using 190 F3 families. Two major quantitative trait loci (QTLs) and two significant digenic epistatic interactions between marker intervals were identified for BPH resistance. One QTL was mapped to 193.4-kb region located on the short arm of chromosome 4, and the other QTL was mapped to a 194.0-kb region on the long arm of chromosome 12. The two QTLs additively increased the resistance to BPH. Markers co-segregating with the two resistance QTLs were developed at each locus. Comparing the physical map positions of the two QTLs with previously reported BPH resistance genes, we conclude that these major QTLs are new BPH resistance loci and have designated them as Bph20(t) on chromosome 4 and Bph21(t) on chromosome 12. This is the first report of BPH resistance genes from the wild species O. minuta. These two new genes and markers reported here will be useful to rice breeding programs interested in new sources of BPH resistance.

PCR Marker-Based Evaluation of the Eating Quality of Japonica Rice (Oryza sativa L.)

Evaluation of eating quality in early breeding generations of rice is critical to developing varieties with better palatability. This paper reports DNA markers associated with eating quality of temperate japonica rice and an evaluation method aided by multiple regression analysis. A total of 30 markers comprising STSs, SNPs, and SSRs were tested for their association with palatability using 22 temperate japonica varieties with different palatability values. Eating quality-related traits of the 22 varieties were also measured. Of the 30 markers, 18 were found to be significantly associated with palatability and, consequently, a model regression equation with an R2 value of 0.99 was formulated to estimate the palatability by the marker data set. Validation of the model equation using selected breeding lines indicated that the marker set and the equation are highly applicable to evaluation of the palatability of cooked rice in temperate japonica varieties.

Identification of QTLs for seed germination capability after various storage periods using two RIL populations in rice

Seed germination capability of rice is one of the important traits in the production and storage of seeds. Quantitative trait loci (QTL) associated with seed germination capability in various storage periods was identified using two sets of recombinant inbred lines (RILs) which derived from crosses between Milyang 23 and Tong 88-7 (MT-RILs) and between Dasanbyeo and TR22183 (DT-RILs). A total of five and three main additive effects (QTLs) associated with seed germination capability were identified in MT-RILs and DT-RILs, respectively. Among them, six QTLs were identified repeatedly in various seed storage periods designated as qMT-SGC5.1, qMT-SGC7.2, and qMT-SGC9.1 on chromosomes 5, 7, and 9 in MT-RILs, and qDT-SGC2.1, qDT-SGC3.1, and qDT-SGC9.1 on chromosomes 2, 3, and 9 in DT-RILs, respectively. The QTL on chromosome 9 was identified in both RIL populations under all three storage periods, explaining up to 40% of the phenotypic variation. Eight and eighteen pairs additive × additive epistatic effect (epistatic QTL) were identified in MT-RILs and DT-RILs, respectively. In addition, several near isogenic lines (NILs) were developed to confirm six repeatable QTL effects using controlled deterioration test (CDT). The identified QTLs will be further studied to elucidate the mechanisms controlling seed germination capability, which have important implications for long-term seed storage.

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.

Isolation and characterization of a dominant dwarf gene, d-h, in rice.

Plant height is an important agronomic trait that affects grain yield. Previously, we reported a novel semi-dominant dwarfmutant, HD1, derived from chemical mutagenesis using N-methyl-N-nitrosourea (MNU) on a japonica rice cultivar, Hwacheong. In this study, we cloned the gene responsible for the dwarf mutant using a map-based approach. Fine mapping revealed that the mutant gene was located on the short arm of chromosome 1 in a 48 kb region. Sequencing of the candidate genes and rapid amplification of cDNA ends-polymerase chain reaction (RACE-PCR) analysis identified the gene, d-h, which encodes a protein of unknown function but whose sequence is conserved in other cereal crops. Real-time (RT)-PCR analysis and promoter activity assays showed that the d-h gene was primarily expressed in the nodes and the panicle. In the HD1 plant, the d-h gene was found to carry a 63-bp deletion in the ORF region that was subsequently confirmed by transgenic experiments to be directly responsible for the gain-of-function phenotype observed in the mutant. Since the mutant plants exhibit a defect in GA response, but not in the GA synthetic pathway, it appears that the d-h gene may be involved in a GA signaling pathway.

Sugary Endosperm is Modulated by Starch Branching Enzyme IIa in Rice ( Oryza sativa L.)

BackgroundStarch biosynthesis is one of the most important pathways that determine both grain quality and yield in rice (Oryza sativa L.). Sugary endosperm, sugary-1 (sug-1), is a mutant trait for starch biosynthesis. Rice plants carrying sug-1 produce grains that accumulate water-soluble carbohydrates instead of starch, even after maturity. Although this trait enhances the diversity of grain quality, sugary endosperm rice has hardly been commercialized due to the severely wrinkled grains and subsequent problems in milling. This study was conducted to identify the genes responsible for the sug-h phenotype through a map-based cloning technology.ResultsWe induced a mild sugary mutant, sugary-h (sug-h) through the chemical mutagenesis on the Korean japonica cultivar Hwacheong. Grains of the sug-h mutant were translucent and amber-colored, and the endosperm appeared less wrinkled than sug-1, whereas the soluble sugar content was fairly high. These characteristics confer greater marketability to the sug-h mutant. Genetic analyses indicated that the sug-h mutant phenotype was controlled by a complementary interaction of two recessive genes, Isoamylase1 (OsISA1), which was reported previously, and Starch branching enzyme IIa (OsBEIIa), which was newly identified in this study. Complementation tests indicated that OsBEIIa regulated the properties of sugary endosperm.ConclusionsComplementary interactions between the starch biosynthesis genes OsISA1 and OsBEIIa determine the mild sugary endosperm mutant, sugary-h, in rice. Our finding may facilitate the breeding of sugaryendosperm rice for commercial benefit.

Yield of maize ( Zea mays L.) logistically declined with increasing length of the consecutive visible wilting days during flowering

Under future climate conditions, the frequency and severity of drought are expected to increase. Maize (Zea mays L.) is susceptible to drought, especially at flowering. The objective of this study was to investigate the effect of consecutive days of visible wilting (DAW) during tassel emergence using two types of Korean maize hybrids, Gwangpyeongok (Gwp; normal) and Ilmichal (Ilmi; waxy). Traits related to plant growth and yield were measured at harvest. Drought stress during tassel emergence significantly reduced the number of green leaves per plant. Silking was delayed due to drought stress during the stage of tassel emergence, although anthesis was only slightly affected, which resulted in an increase in the anthesis-silking interval (ASI). For each DAW, ASI increased by 1.6 days and 0.8 days for Gwp and Ilmi, respectively. The number of green leaves and ASI showed strong correlation with DAW length and grain yield, which suggested that those factors may be selective traits for drought tolerance at flowering. The filled grain number per plant declined logistically with increasing DAW due to reductions in kernels per row and percentage of filled grains. The filled grain number per plant significantly declined starting at 5 and 10 DAW in Gwp and Ilmi, respectively, which indicated that drought stress effects are dependent on drought severity and the genetic characteristics of specific hybrids. Probit analysis revealed that DAW causing 50% reduction in maize grain yield was about 4.7 and 6.3 days in Gwp and Ilmi, respectively, which resulted in about 13.6% and 9.2% reduction in grain yield per day of DAW, respectively. These results indicate that Gwangpyeongok is more sensitive to drought stress during flowering than Ilmichal.

Physiological and Protein Profiling Response to Drought Stress in KS141, a Korean Maize Inbred Line

Understanding the complex response mechanism of a crop to drought is the major step in the developing of tolerant genotypes. In our study, to investigate physiological traits and proteome dynamics, an inbred maize (Zea mays L.) line (KS141) was subjected to 10 days of water-withholding at the V5 or V6 leaf stage. The subsequent analysis of their physiological parameters revealed a decreased relative leaf water content, Fv/Fm, stomatal conductance, net CO2 assimilation rate, leaf transpiration, and water use efficiency, resulting in severe growth retardation of leaf area, stem length and width, aerial part, and root dry matter at 3 and 10 days after withholding water. However, aerial part and root dry matter were little changed during drought stress for 3 days. To understand the proteome dynamics during the 10-day drought stress in maize leaves, comparative proteome analysis was carried out between the well-watered and drought-treated leaves. Proteins were extracted using phenol extraction method from leaves with/without drought stress, and then separated by 2-DE. After 2-DE gel analyses, 14 differentially expressed protein spots were identified by MALDITOF mass spectrometry. Out of 14, eleven and three protein spots were found to be up- or down-regulated, respectively. Interestingly, stress-related proteins such as glutathione S-transferase, abscisic stress-ripening proteins, and pathogenesis-related proteins were increased by drought stress. Our study may provide molecular mechanisms and selective markers for drought tolerant maize genotypes.

Impact of the consecutive days of visible wilting on growth and yield during tassel initiation in maize ( Zea Mays L.)

Maize (Zea mays L.) is a major crop with different uses but shows significant susceptibility to drought stress. Recent climate change has caused prolonged drought stress, but in most countries maize production relies on rain-fed cultivation. This study was to investigate the impact of the consecutive days of visible wilting (DAW) during tassel initiation (V6) using two types of Korean maize hybrids, Gwangpyeongok (GWP) and Ilmichal (Ilmi). The traits related to plant growth and yield were measured at harvest. Drought stress during tassel initiation linearly reduced plant elongation and dry matter accumulation with the length of DAW increasing but did not affect the leaf number per plant. Our results from the simple linear regression analysis indicated that silking of GWP and Ilmi would be delayed by 0.78 and 0.61 days per DAW, respectively, which was similar to anthesis. Still, little change was observed for interval between anthesis and silking under the same condition. The kernels per row were very dependent on the length of DAW but the rows per ear were not. The percentage of filled grains and the 100- grain weight were significantly reduced only at 15- or 20-DAW and more markedly so in Gwangpyeongok at 20-DAW. The filled grain number per plant showed a gradual logistical decline mainly due to decreases in the kernels per row. All these reductions may be because initiation and growth of tassel, ear, and kernels and internode elongation beginning around V6 are sensitive to water deficits. Probit analysis revealed that the DAW to cause 50% reduction in plant grain yield was about 12 and 20 days in GWP and Ilmi, resulting in about 4.5 and 2.7% reduction a day of DAW, respectively. These results indicate that Gwangpyeongok may be more sensitive to drought stress during tassel initiation than Ilmichal.

Evaluation of waterlogging tolerance with the degree of foliar senescence at early vegetative stage of maize ( Zea mays L.)

Maize is highly susceptible to waterlogging, which is becoming one of worldwide abiotic threats in many agricultural areas. This study was evaluated to establish the screening method and to find tolerant maize genotypes. Six Korean maize inbred lines were subjected to waterlogging at V3 for 15 days using a big size pot with single maize plant (big pot method) and a box containing 31 maize plants at a time (box method). The degree of foliar senescence and the number of senescent leaves were better indicators for selecting waterlogging tolerant maize genotypes than SPAD value and plant height. The degree of foliar senescence revealed that KS124, KS140, and KS141 are tolerant, and KS85 is susceptible to waterlogging at the early growth stage. These responses of foliar senescence were in clear accordance with those of plant grain yield, which was supported by stress tolerance index for grain yield. The box method also showed the similar response of foliar senescence to the big pot method. Therefore, this box method based on foliar senescence may be simple and efficient for large-scale screening of maize germplasm against waterlogging stress. It was concluded that foliar senescence can be a good indicator for selecting tolerant maize genotypes against waterlogging at the early growth stage.