Gene flow from transgenic rice to red rice (Oryza sativa L.) in the field

In this study, we simulate a transgenic rice crop highly infested with red rice to examine transgene transfer from a transgenic line (A2504) resistant to glufosinate ammonium to cohabitant red rice. The red rice was sown along with the transgenic line at the highest density found in naturally infested crops in the region. Agricultural practices similar to those used to control red rice infestation in northern Italy rice fields were used to reproduce the local rice production system. During the first 2 years, the field was treated with herbicide at the appropriate time; in the first year the dosage of herbicide was three times the recommended amount. In this first year, detectable red rice plants that escaped herbicide treatment were manually removed. Nevertheless, two herbicide‐resistant hybrid plants (named 101 and 104) were identified in the experimental field during the second year of cultivation. Phenotypic and molecular characterisation suggests the hybrid nature of these two plants, deriving from crossing events involving A2504, respectively, with red rice (plant 101) and the buffer cultivar Gladio (plant 104). The progeny of two subsequent generations of the two plants were examined and the presence of the transgene detected, indicating stable transfer of the transgene across generations. In conclusion, despite control methods, red rice progeny tolerant to the herbicide can be expected following use of transgenic rice and, consequently, difficulties in controlling this weed with chemicals will emerge in a relatively short time.     

The miR156‐SPL9‐DFR pathway coordinates the relationship between development and abiotic stress tolerance in plants

Young organisms have relatively strong resistance to diseases and adverse conditions. When confronted with adversity, the process of development is delayed in plants. This phenomenon is thought to result from the rebalancing of energy, which helps plants to coordinate the relationship between development and stress tolerance; however, the molecular mechanism underlying this phenomenon remains mysterious. In this study, we found that miR156 integrates environmental signals to ensure timely flowering, thus enabling the completion of breeding. Under stress conditions, miR156 is induced to maintain the plant in the juvenile state for a relatively long period of time, whereas under favorable conditions, miR156 is suppressed to accelerate the developmental transition. Blocking the miR156 signaling pathway in Arabidopsis thaliana with 35S::MIM156 (via target mimicry) increased the sensitivity of the plant to stress treatment, whereas overexpression of miR156 increased stress tolerance. In fact, this mechanism is also conserved in Oryza sativa (rice). We also identified downstream genes of miR156, i.e. SQUAMOSA PROMOTER BINDING PROTEIN‐LIKE 9 (SPL9) and DIHYDROFLAVONOL‐4‐REDUCTASE (DFR), which take part in this process by influencing the metabolism of anthocyanin. Our results uncover a molecular mechanism for plant adaptation to the environment through the miR156‐SPLs‐DFR pathway, which coordinates development and abiotic stress tolerance.     

海南普通野生稻稻瘟病的抗性鉴定与评价

在苗期应用自然诱发鉴定法对海南普通野生稻(Oryza rufipogonGriff.)41个居群的410份材料进行了2年的稻瘟病(rice blast)抗性鉴定,结果表明:经过初鉴和复鉴,410份海南普通野生稻中有21份表现高抗,占5.1%,117份表现抗,占28.5%,说明海南普通野生稻具有较好的稻瘟病抗性。     

Genotypic variations in carbon isotope discrimination, transpiration efficiency, and biomass production in rice as affected by soil water conditions and N

Genotypic and environmental (soil water regime and N level) variation in carbon isotope discrimination (CID) in relation to the gas exchange, transpiration efficiency (A/T), and biomass production were investigated in field experiments using eleven rice (Oryza sativa L.) genotypes. The results showed that genotype was more dominant for variation in CID than in total biomass. Genotypic ranking in CID was consistent across environments because of small genotype × environment interactions. Japonica genotypes tended to have lower CID than indica genotypes. Higher soil water and lower N rate significantly increased CID. Variation in CID was slightly smaller for water regime than for genotype. There was a negative correlation between CID andA/T among genotypes within water regimes. Genotypic variation in CID was associated mainly with variation in stomatal conductance under all soil water regimes and with photosynthetic capacity in late growth stages under aerobic soil conditions. The decrease in CID at higher N was probably due to lower stomatal conductance under aerobic soil conditions and to higher photosynthetic rates under submerged soil conditions. The correlation between biomass and CID was not clear in aerobic soil, whereas it was positive in submerged soil, which indicated that the significance of lower or higher CID for improving biomass productivity may differ under different soil water regimes. Overall, the results implied a possible use of CID as a selection criterion for genotypic improvement inA/T and productivity in rice.     

Map-based cloning of a fertility restorer gene, Rf-1, in rice (Oryza sativa L.)

A rice nuclear gene, Rf-1, restores the pollen fertility disturbed by the BT-type male sterile cytoplasm, and is widely used for commercial seed production of japonica hybrid varieties. Genomic fragments carrying Rf-1 were identified by conducting chromosome walking and a series of complementation tests. Isolation and analysis of cDNA clones corresponding to the fragments demonstrated that Rf-1 encodes a mitochondrially targeted protein containing 16 repeats of the 35-aa pentatricopeptide repeat (PPR) motif. Sequence analysis revealed that the recessive allele, rf-1, lacks one nucleotide in the putative coding region, presumably resulting in encoding a truncated protein because of a frame shift. Rice Rf-1 is the first restorer gene isolated from cereal crops that has the property of reducing the expression of the cytoplasmic male sterility (CMS)-associated mitochondrial gene like many other restorer genes. The present findings may facilitate not only elucidating the mechanisms of male sterility by the BT cytoplasm and its restoration by Rf-1 but also isolating other restorer genes from cereal crops, especially rice.     

Infection with the parasitic angiosperm Striga hermonthica influences the response of the C3 cereal Oryza sativa to elevated CO2

Upland rice (Oryza sativa L.) was grown at both ambient (350 μmol mol^?1) and elevated (700 μmol mol^?1) CO₂ in either the presence or absence of the root hemi‐parasitic angiosperm Striga hermonthica (Del) Benth. Elevated CO₂ alleviated the impact of the parasite on host growth: biomass of infected rice grown at ambient CO₂ was 35% that of uninfected, control plants, while at elevated CO₂, biomass of infected plants was 73% that of controls. This amelioration occurred despite the fact that O. sativa grown at elevated CO₂ supported both greater numbers and a higher biomass of parasites per host than plants grown at ambient CO₂. The impact of infection on host leaf area, leaf mass, root mass and reproductive tissue mass was significantly lower in plants grown at elevated as compared with ambient CO₂. There were significant CO₂ and Striga effects on photosynthetic metabolism and instantaneous water‐use efficiency of O. sativa. The response of photosynthesis to internal [CO₂] (A/C_i curves) indicated that, at 45 days after sowing (DAS), prior to emergence of the parasites, uninfected plants grown at elevated CO₂ had significantly lower CO₂ saturated rates of photosynthesis, carboxylation efficiencies and ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco; EC 4.1.1.39) contents than uninfected, ambient CO₂‐grown O. sativa. In contrast, infection with S. hermonthica prevented down‐regulation of photosynthesis in O. sativa grown at elevated CO₂, but had no impact on photosynthesis of hosts grown at ambient CO₂. At 76 DAS (after parasites had emerged), however, infected plants grown at both elevated and ambient CO₂ had lower carboxylation efficiencies and Rubisco contents than uninfected O. sativa grown at ambient CO₂. The reductions in carboxylation efficiency (and Rubisco content) were accompanied by similar reductions in nitrogen concentration of O. sativa leaves, both before and after parasite emergence. There were no significant CO₂ or infection effects on the concentrations of soluble sugars in leaves of O. sativa, but starch concentration was significantly lower in infected plants at both CO₂ concentrations. These results demonstrate that elevated CO₂ concentrations can alleviate the impact of infection with Striga on the growth of C₃ hosts such as rice and also that infection can delay the onset of photosynthetic down‐regulation in rice grown at elevated CO₂.     

Rice genetic resources: history,conservation, investigative characterization and use in Japan

Rice has been grown in Japan for about 3000 years. Although both japonica and indica varieties have been grown in Japan, now japonica rices are grown. Japanese rice breeding has used an ecological breeding approach. While emphasis in rice breeding in the 1940's and 1950's focussed on yield in recent decades quality has been of major importance. Consumer preference and name recognition of high quality varieties, such as Koshihikari, has resulted in slow acceptance of new varieties.Rice germplasm was systematically collected throughout Japan between 1962 and 1963. Subsequent acquisition and collecting, in Japan and other countries, has resulted in 28,000 accessions being conserved in the National Genebank, based at the National institute of Agrobiological Resources (NIAR).Research on genetic diversity of rice using a range of techniques, for example esterase isozymes, has revealed clinal variation in rice radiating from the center of diversity of rice in and around southwest China. Newly found genes in traditional rice germplasm, such as genes for non-elongating mesocotyl, are now routinely identified on the rice genome. Pioneering studies on eco-genetic differentiation of species in the genus Oryza in Japan has revealed much about the complex genepool for which rice evolved.Pest and disease resistance sources, particularly to blast, bacterial blight and brown plant hopper, from many countries have been incorporated into Japanese varieties. Cold tolerance at the booting stage was found in the Indonesian variety Silewah. In the future in characterisation of rice germplasm and interaction between rice germplasm specialists and rice molecular scientists, both in Japan and internationally, will be corner stones to securing rice genetic diversity and rice improvement in the next century.     

Differentiation of a Miniature Inverted Transposable Element （MITE） System in Asian Rice Cultivars and Its Inference for a Diphyletic Origin of Two Subspecies of Asian Cultivated Rice

In the present study, we report a survey on a Miniature Inverted Transposable Element （MITE） system known as mPing in 102 varieties of Asian cultivated rice （Oryza sativa L.）. We found that mPing populations could be generalized Into two families, mPing-1 and mPing-2, according to their sequence structures. Further analysis showed that these two families of mPing had significant bias in their distribution pattern in two subspecies of rice, namely O. sativa ssp. japonica and indica. 0. sativa japonica has a higher proportion of mPing-1 as a general trait, whereas 0. sativa indica has a higher proportion of roPing-2. We also examined the mPing system In a doubled haploid （DH） cross-breeding population of jingxi 17 （japonica） and zhaiyeqing 8 （indica） varieties and observed that the mPing system was not tightly linked to major subspecies-determining genes. Furthermore, we checked the mPing system in 28 accessions of Asian common wild rice O. rufipogon and found the roPing system in 0. rufipogon. The distribution pattern of the roPing system in O. rufipogon indicated a diphyletlc origin of the Asian cultivated rice O. sativa species. We did not find the mPing system in another 20 Oryza species. These results substantiated a previous hypothesis that O. ruflpogon and O. nivara species were the closest relatives of O. sativa and that the two extant subspecies of O. sativa were evolved independently from corresponding ecotypes of O. ruflpogon.