Koshihikari Research Articles

Potassium transporter OsHAK17 may contribute to saline-alkaline tolerant mechanisms in rice (Oryza sativa).

Rice production is seriously affected by saline-alkaline stress worldwide. To elucidate the saline-alkaline tolerance mechanisms in a novel tolerant rice variety, Shwe Nang Gyi (SNG), we investigated ion accumulation in SNG and Koshihikari (KSH), which is a saline-alkaline sensitive rice variety, and the candidates for saline-alkaline inducible genes in SNG using RNA-seq. SNG had superior ion accumulation capacity, such as K and Zn, compared to KSH. In contrast, SNG accumulated the same level of Na content in its leaf blades as KSH despite the higher dry weight of the SNG leaf blades. We further found that the expression of numerous genes, including several K+ transporter/high-affinity K+ transporter/K+ uptake protein/K+ transporter (HAK/KUP/KT) family members, were upregulated in SNG, and that OsHAK17 and OsHAK21 expression levels in the roots were significantly higher in SNG than in KSH. Moreover, yeast complementation analysis revealed that OsHAK17 was involved in K+ uptake under high-Na conditions. These results suggested that SNG has an effective K+ acquisition system supported by OsHAK17 functioning in saline-alkaline environments.

Effects of Water Management and Rice Varieties on Greenhouse Gas Emissions in Central Japan

Greenhouse gas (GHG) emissions from paddy fields depend on water management practices and rice varieties. Lysimeter experiments were conducted to determine the effect of rice varieties (lowland; Koshihikari (KH) and upland; Dourado Precoce (DP)) on GHG emissions under two water management practices: alternate wetting and drying (AWD) and continuous flooding (CF). A repeated cycle of drying and wetting in AWD irrigation was performed by drying the soil to −40 kPa soil matric potential and then rewetting. Consequently, the closed chamber method was used to measure direct emissions of methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2). The result revealed that water management significantly affected CH4 and N2O emissions (p < 0.05), while no significant effect was observed between different rice varieties. Although, AWD irrigation reduced CH4 emissions, it increased N2O emissions compared to CF irrigation, likely due to increased oxygen supply. AWD irrigation decreased GWP by 55.6% and 59.6% in KH and DP, respectively, compared to CF irrigation. Furthermore, CH4 and N2O emissions significantly correlated with soil redox potential and volumetric water content. These results suggest that AWD irrigation might be an effective water management method for mitigating GHG emissions from rice fields in central Japan.

A MAPKKK gene from rice, RBG1res, confers resistance to Burkholderia glumae through negative regulation of ABA

Burkholderia glumae causes bacterial seedling rot (BSR) of rice and is a threat to a consistent food supply. When previously screening for resistance against B. glumae in the resistant cultivar Nona Bokra (NB) versus the susceptible cultivar Koshihikari (KO), we detected a gene, Resistance to Burkholderia glumae 1 (RBG1), at a quantitative trait locus (QTL). Here, we found that RBG1 encodes a MAPKKK gene whose product phosphorylates OsMKK3. We also found that the kinase encoded by the RBG1 resistant (RBG1res) allele in NB presented higher activity than did that encoded by the RBG1 susceptible (RBG1sus) allele in KO. RBG1res and RBG1sus differ by three single-nucleotide polymorphisms (SNPs), and the G390T substitution is essential for kinase activity. Abscisic acid (ABA) treatment of inoculated seedlings of RBG1res-NIL (a near-isogenic line (NIL) expressing RBG1res in the KO genetic background) decreased BSR resistance, indicating that RBG1res conferred resistance to B. glumae through negative regulation of ABA. The results of further inoculation assays showed that RBG1res-NIL was also resistant to Burkholderia plantarii. Our findings suggest that RBG1res contributes to resistance to these bacterial pathogens at the seed germination stage via a unique mechanism.

Comparisons of the stomatal conductance and electron transport rate of three Japanese rice cultivars including Himenorin in Ehime Prefecture

This study focused on stomatal conductance (gs) and electron transport rate (ETR) as one possible approach to the mechanisms of controlling canopy temperature and photosynthetic traits in rice. Three Japanese rice cultivars, Koshihikari (KH), Nikomaru (NM), and the new cultivar Himenorin (HR) developed in Ehime Prefecture were selected for the experiment. From the uppermost to the fifth leaves of five or more rice plants of each cultivar, gs and ETR were measured in situ using a handheld porometer/fluorometer. The results revealed the highest gs in HR among the three cultivars in all leaf positions from before the flag leaf extension until the maturity stage, which could be regarded as one of the advantageous mechanisms for moderating the thermal condition of the canopy with larger transpiration and supporting a higher photosynthetic level. The ETR of HR was highest among the three cultivars in most leaf positions from the heading stage to the maturity stage, which could be expected to maintain a higher photosynthetic level. These traits of gs and ETR in HR compared with NM and KH could be assessed as possible synergistic mechanisms for higher production and quality of rice with higher photosynthetic potential.

Elevated CO2 enhances rice root growth under alternate wetting and drying irrigation by involving ABA response: Evidence from the seedling stage

AbstractThe atmospheric CO2 enrichment can seriously affect rice root growth. Alternate wetting and drying (AWD) irrigation, which can also increase root growth, is a widely promoted water‐saving technology for future climate, yet how elevated CO2 (eCO2) influences rice root growth under AWD remains unclear. In the present study, we examined the root growth of Yangdao 6 (YD 6) and Koshihikari (KOS) cultured under different water irrigation regimes (well‐watered and AWD) and CO2 concentration (400 and 800 ppm). AWD reduced shoot dry weight of KOS compared with WW under ambient CO2 (400 ppm, aCO2), while the shoot dry weight of KOS showed no difference between WW and AWD treatments under eCO2. Additional, under aCO2, AWD did not affect the exhibited similar root dry weight, length, total surface area, and volume of YD 6 and KOS relative to WW. However, under eCO2, AWD significantly promoted the root dry weight, root length, total root surface area, and root volume of YD 6 and KOS. Furthermore, root ABA content of YD 6 and KOS was significantly higher under AWD than under WW. Then, the OsNCED3 (a key gene for ABA biosynthesis) RNAi lines were used to check the role of ABA in root growth under eCO2 with AWD conditions. The results showed that AWD increased the ABA content and root parameters of WT but not the OsNCED3 RNAi lines under eCO2. Overall, the results suggest that eCO2 can improve rice root growth under AWD by involving root ABA, which contributes to the understanding of water‐saving irrigation on rice in the future climate.

A Koshihikari X Oryza rufipogon Introgression Line with a High Capacity to Take up Nitrogen to Maintain Growth and Panicle Development under Low Nitrogen Conditions.

Nitrogen (N) is an important macronutrient for plant growth and development. Currently, N fertilizers are required for the efficient production of modern crops such as rice due to their limited capacity to take up N when present at low concentrations. Wild rice represents a useful genetic resource for improving crop responses to low nutrient stress. Here, we describe the isolation and characterization of an introgression line, KRIL37, that carries a small region of the Oryza rufipogon genome in the Oryza sativa L. cv Koshihikari (KH) background. This line was found to grow better under low N conditions and have similar or lower C/N ratios in aerial portions compared to those in the parental KH cultivar, suggesting that KRIL37 has a higher capacity to take up and assimilate N when present at low concentrations. KRIL37 performance in the field was also better than that of KH cultivated without N and fertilizer (-F). Transcriptome analyses of 3-week-old seedlings based on RNA-sequencing revealed that KH induced a wider suite of genes than the tolerant line KRIL37 in response to low N conditions. Some ammonium transporters and N assimilation genes were found to be induced under low N in KRIL37, but not in KH. Our findings suggest that the superior growth performance of KRIL37 under limited N conditions could be due to the expression of wild alleles influencing N uptake and assimilation. Our study demonstrates the potential to use wild rice genomes to improve modern crops for low nutrient tolerance.

QTL Analysis Revealed One Major Genetic Factor Inhibiting Lesion Elongation by Bacterial Blight (Xanthomonas oryzae pv. oryzae) from a japonica Cultivar Koshihikari in Rice.

Xanthomonas oryzae pv. oryzae (Xoo) is a pathogen that has ravaged the rice industry as the causal agent of bacterial blight (BB) diseases in rice. Koshihikari (KO), an elite japonica cultivar, and ARC7013 (AR), an indica cultivar, are both susceptible to Xoo. Their phenotypic characteristics reveal that KO has shorter lesion length than that of AR. The F2 population from KO × AR results in continuous distribution of lesion length by inoculation of an Xoo race (T7147). Consequently, quantitative trait loci (QTL) mapping of the F2 population is conducted, covering 12 chromosomes with 107 simple sequence repeat (SSR) and insertion/deletion (InDel) genetic markers. Three QTLs are identified on chromosomes 2, 5, and 10. Of them, qXAR5 has the strongest resistance variance effect of 20.5%, whereas qXAR2 and qXAR10 have minor QTL effects on resistance variance, with 3.9% and 2.3%, respectively, for a total resistance variance of 26.7%. The QTLs we examine for this study differ from the loci of BB resistance genes from earlier studies. Our results can help to facilitate understanding of genetic and morphological fundamentals for use in rice breeding programs that are more durable against evolving Xoo pathogens and uncertain climatic temperature.

Potential marker proteins for ozone-induced yield reduction in rice

Three proteins - a 60-kDa chaperonin (CPN-60), chloroplastic ATP synthase, and enolase 1 - were evaluated as potential markers of ozone-induced yield responses in six rice (Oryza sativa L.) cultivars (‘Kirara 397’, ‘Koshihikari’, ‘Nipponbare’, ‘Takanari’, ‘Kasalath’, ‘Suphanburi 90’) under ozone stress in laboratory-scale tests. The levels of all three proteins decreased after ozone exposure in cultivars identified as ozone-sensitive while they increased or remained constant after ozone exposure in tolerant cultivars, although ATP synthase tended to decrease. Furthermore, the protein level and grain yield in each cultivar exposed to ozone were significantly positively correlated for all three proteins. Thus, CPN-60 and enolase 1 are potential markers for chronic ozone stress in rice

Vulnerability of lodging risk to elevated CO2 and increased soil temperature differs between rice cultivars

Anthropogenic increases in atmospheric carbon dioxide concentration [CO2], and subsequent increases in surface temperatures, are likely to impact the growth and yield of cereal crops. One potential means for yield reduction is for climate parameters to increase the occurrence of lodging. Using an in situ free-air CO2 enrichment (FACE) system, two morphologically distinct rice cultivars, KH (Koshihikari) and SY (Shan you 63), were grown at two [CO2]s (ambient and ambient+200μmolmol−1) and two soil temperatures (ambient and ambient±1.8°C) over a two year period to assess and quantify lodging risk. Elevated [CO2] per se had no effect on lodging resistance for either cultivar. However, elevated [CO2] and higher soil temperature increased the lodging risk for SY, due to a relatively higher increase in plant biomass and height at the elevated, relative to the ambient [CO2] condition. Elevated soil temperature per se also increased lodging risk for both cultivars and was associated with longer internodes in the lower portion of the tillers. These findings illustrate that lodging susceptibility in rice, an important cereal crop, can be increased by rising [CO2] and soil temperature; however, variation observed here between rice cultivars suggests there may be sufficient intraspecific variability to begin choosing rice lines that minimize the potential risk of lodging.

수분-열처리로 제조한 멥쌀가루의 호화 특성과 겔 강도

Heat-moisture treatment (HMT) was applied to 4 samples of rice flours, Goami (GM), Taeguk (TG), Choochung (CC) and Koshihikari (KSHK), of which amylose contents were 31.5, 32.3, 24.3, and 23.3%, respectively. Wet-milled rice flours were dried, moisture content adjusted to 21, 24, 27 and 30%, respectively, and autoclaved at 100 and for 30~90 min. The changes on swelling, solubility, RVA (rapid visco analyser) paste viscosities and gel strength were observed. In GM and TG, peak viscosity (PV) and breakdown (BD) decreased and no peak appeared as moisture and treatment time increased by HMT. In CC, FV increased notably with big increase of PV and setback (SB) by HMT compared to the other rice flours. BD in all the samples decreased as moisture, temperature, and time increased by HMT. RVA pasting properties of HMT GM and HMT TG were changed remarkably under conditions of moisture 21%, and 30 min whereas for HMT CC and HMT KSHK, higher temperature or more time was required at the same mois ture levels. The swelling power, solubility and gel strength increased by HMT. Gel strength correlated positively with SB (r

Planting Density Suitable for Late Transplanting for Avoiding High Temperature During the Ripening Period of Rice Cultivar Koshihikari in Toyama Prefecture, Japan

近年の温暖化条件下において，高温登熟回避を想定した作期移動が水稲「コシヒカリ」の生育，収量および品質に及ぼす影響を調査するとともに，作期ごとの適正な栽植密度について2ヶ年検討した．移植時期を4月下旬 （早植） から5月中旬 （晩植） に遅らせた結果，5月中旬区では4月下旬区に比べて移植～最高分げつ期までの日数が短縮することで最高分げつ数が減少し，穂数が少なくなることで減収した．また，晩植によって登熟気温が低下した2005年では5月中旬区で外観品質が向上した．各移植時期において栽植密度と収量，品質との関係を検討した結果，4月下旬区では栽植密度を高めることで穂数が増加するものの収量は増加せず，過繁茂による葉色の低下や品質の低下が認められた．一方，5月中旬区では，晩植による穂数不足を補うために栽植密度を高めることが有効であり，栽植密度を高めるほど穂数増加，収量増加につながるとともに，外観品質が向上することが明らかになった．これらのことから，高温登熟回避を想定した晩植栽培では，早植栽培に比べて栽植密度を高めることが生育，収量および品質の安定化に有効であると判断された．

Lodging-related Characteristics of Hikari-Shinseiki, an Isogenic Variety of Koshihikari

十石に由来する半矮性遺伝子sd1を持つコシヒカリ同質遺伝子品種であるヒカリ新世紀の倒伏関連形質について, 堆肥施用条件下において検討した. ヒカリ新世紀の最長稈長や平均稈長はコシヒカリに比べていずれも短く, 短稈品種であった. 出穂期後26～30日に測定したヒカリ新世紀の第4節間(穂首節間を第1節間とする)の挫折荷重はコシヒカリと同等の強度を示した. このときのヒカリ新世紀の曲げモーメント(挫折荷重を測定した節間以上の長さと重さの積)はコシヒカリに比べて小さく, これは短稈化による地上部長の短縮による影響が大きかった. このため, ヒカリ新世紀の倒伏指数(曲げモーメント・挫折荷重-1・100)は127～100で, コシヒカリの173～148に比べて小さかった. 倒伏のみられた年次の収穫期におけるヒカリ新世紀の倒伏程度(0 : 倒伏無～4 : 倒伏程度甚の5段階表示)は1.1 で, コシヒカリの2.6 に比べて小さく, 倒伏指数の小さいことと対応した関係がみられた. 以上のことから, ヒカリ新世紀の耐倒伏性が優れた要因は, 倒伏関連形質からみると, 曲げモーメントの低下による影響が大きく, 第4節間の強度には影響されないと判断された.

Structural Properties of Amylopectins Corresponding to Physical Properties of Rice Starches Appropriate for Sake

Starches from a variety of Sake-rice (Yamadanishiki, Gohyakumangoku, Miyamanishiki, Kitanishiki and Wakamizu) which are suitable for Sake brewing were investigated by comparing them with Koshihikari starch to recognize their structural properties of amylopectins. The partial hydrolysate (about 15% hy drolysis) of starch with isoamylase was fractionated into three fractions (fr.1, fr.2 and fr.3) by gel permeation chromatography (GPC) with a Toyopearl HW-50S, and then the short-amylose chains derived mainly from the outer portion of the amylopectin collected in the fr.3 were analyzed by a HPAEC-system equipped with a pulsed amperometric detector (HPAEC-PAD). From comparison of the chain-length distributions between Sake-rice starches and that of Koshihikari, it was found that Sake-rice amylopectins were plentiful in longish chains around DP 13-23 and scarce in shortish chains around DP 6-12, suggesting a structural property susceptible to retrogradation. The pasting properties of Sake-rice starches analyzed by Rapid Visco Analyzer (RVA) showed higher pasting temperature (PT), higher setback (SB), and lower breakdown (BD) than Koshi hikari starch, suggesting the outer portions of amylopectin had abundant longish debranched short side chains. These results suggested that rice starches with amylopectins susceptible to retrogradation are adequate for Sake-rice.