Wild Rice Plants Research Articles

Virome Characterization of Native Wild-Rice Plants Discovers a Novel Pathogenic Rice Polerovirus With World-Wide Circulation.

Pandemics originating from zoonotic viruses have posed significant threats to human health and agriculture. Recent discoveries have revealed that wild-rice plants also harbour viral pathogens capable of severely impacting rice production, a cornerstone food crop. In this study, we conducted virome analysis on ~1000 wild-rice individual colonies and discovered a novel single-strand positive-sense RNA virus prevalent in these plants. Through comprehensive genomic characterization and comparative sequence analysis, this virus was classified as a new species in the genus Polerovirus, designated Rice less tiller virus (RLTV). Our investigations elucidated that RLTV could be transmitted from wild rice to cultivated rice via a specific insect vector, the aphid Rhopalosiphum padi, causing less tiller disease symptoms in rice plants. We generated an infectious cDNA clone for RLTV and demonstrated systemic infection of rice cultivars and induction of severe disease symptoms following mechanical inoculation or stable genetic transformation. We further illustrated transmission of RLTV from stable transgenic lines to healthy rice plants by the aphid vector, leading to the development of disease symptoms. Notably, our database searches showed that RLTV and another polerovirus isolated from a wild plant species are widely circulating not only in wild rice but also cultivated rice around the world. Our findings provide strong evidence for a wild plant origin for rice viruses and underscore the imminent threat posed by aphid-transmitted rice Polerovirus to rice cultivar.

New persistent plant RNA virus carries mutations to weaken viral suppression of antiviral RNA interference.

Persistent plant viruses are widespread in natural ecosystems. However, little is known about why persistent infection with these viruses may cause little or no harm to their host. Here, we discovered a new polerovirus that persistently infected wild rice plants by deep sequencing and assembly of virus-derived small-interfering RNAs (siRNAs). The new virus was named Rice tiller inhibition virus 2 (RTIV2) based on the symptoms developed in cultivated rice varieties following Agrobacterium-mediated inoculation with an infectious RTIV2 clone. We showed that RTIV2 infection induced antiviral RNA interference (RNAi) in both the wild and cultivated rice plants as well as Nicotiana benthamiana. It is known that virulent virus infection in plants depends on effective suppression of antiviral RNAi by viral suppressors of RNAi (VSRs). Notably, the P0 protein of RTIV2 exhibited weak VSR activity and carries alanine substitutions of two amino acids broadly conserved among diverse poleroviruses. Mixed infection with umbraviruses enhanced RTIV2 accumulation and/or enabled its mechanical transmission in N. benthamiana. Moreover, replacing the alanine at either one or both positions of RTIV2 P0 enhanced the VSR activity in a co-infiltration assay, and RTIV2 mutants carrying the corresponding substitutions replicated to significantly higher levels in both rice and N. benthamiana plants. Together, our findings show that as a persistent plant virus, RTIV2 carries specific mutations in its VSR gene to weaken viral suppression of antiviral RNAi. Our work reveals a new strategy for persistent viruses to maintain long-term infection by weak suppression of the host defence response.

Mechanism of betterment towards growth and induction of defense in rice (Oryza sativa L.) by biopriming with bacterial endophytes isolated from wild rice

Utilizing beneficial microorganisms associated with plants, particularly endophytes, is becoming more and more prevalent since it supports the physiological health and evolutionary adaption of the host. The range of enhanced endophytic bacteria found in wild rice makes it a promising resource for sustainable agriculture. Current study focused on bacterial endophytes the tissues of wild rice plants' roots, stems, and leaves for managing the health and development of rice (Oryza sativa L.) plants. Bacterial endophytes were characterized using 16S rRNA. Treatments with Priestia megaterium (NRRI EB 1) and Priestia aryabhattai (NRRI EB 2) outperformed the other isolates in rice growth enhancement activities significantly. The biocontrol efficacy of bacterial endophytes was tested against Xanthomonas oryzae pv. oryzae and Rhizoctonia solani and percentage of inhibition was the higher in NRRI EB 1 by 79.32-80.83% and in NRRI EB 2 by 79.69-80.45%. Bio-priming the seeds with specific endophytic bacterial strains led to a decrease in average germination time, an increase in seedling vigor, and total chlorophyll content. Additionally, they generated greater amounts of soluble phosphate (40.91-83.70 μg/mL) and indole acetic acid (28.10-60.18 μg/mL), which are in the midst of encouraging more plant development. Higher expressions of defense enzymes in comparison to the control, including catalase (>220% in root and shoot), peroxidase (>200% in shoot and root), and superoxide dismutase (> 150% in shoot and root) illustrates the rice crop's resilience to withstand stress. The activity of the mentioned enzymes was further validated through the activation of corresponding defense genes such as DEFENSIN (>2-fold), PAL (>3-fold), PR-3 (>2-fold), POX (>2-fold) and LOX (>1-fold) relative to the control's untreated plants. The possibility exists to extract advantageous endophytic bacteria from wild rice species, potentially rewilding the microbiome of farmed rice cultivators and fostering their development.

Characterization of endophytic bacteria isolated from wild rice plants in the Mekong Delta, Vietnam

Abstract. Thi QVC, Minh NLK, Thuy NP, Tat TQ, Tran T. 2024. Characterization of endophytic bacteria isolated from wild rice plants in the Mekong Delta, Vietnam. Biodiversitas 25: 2576-2585. Endophytic bacteria bring many benefits to plants, such as stimulating plant growth and inhibiting many microbial pathogens that cause plant diseases. Hence, this investigation aimed to evaluate the association of endophytic bacteria with wild rice (Oryza rufipogon) that can fix nitrogen, solubilize phosphorus and produce indole-3-acetic acid (IAA). Twelve-five bacterial strains were recovered from wild rice stems and roots collected from Vinh Long and Tien Giang provinces of the Mekong Delta. Among these strains, six had phosphorus solubilizing and seven had nitrogen-fixing activity. Strain BR3.5 fixed the highest nitrogen, i.e. ammonia (NH4+) content of 0.109 ± 0.002 mg/L after eight-day incubation. However, the highest phosphorus solubilization was recorded in two isolates, RR3.7 and RR1.1, with clear zone diameters of 0.800 ± 0.020 mm and 0.800 ± 0.030 mm, respectively. In addition, bacterial strains could synthesize IAA, and BR2.5 produced the highest, i.e., 0.067 ± 0.002 ?g/mL, IAA after eight-day incubation. Notably, strain BR3.5 exhibited multiple activities like nitrogen fixation (0.109 ± 0.002 mg/L), phosphorus solubilization (1.02 ± 0.002 mm), and IAA synthesis (0.056 ± 0.00 ?g/mL). Strain BR3.5 was identified as Pantoea sp. based on 16S rRNA gene sequencing (92.69% similarity) together with morpho-physiological and biochemical characteristics. The findings indicate that strain BR3.5 may be used for the production of biofertilizers for rice farming.

Comprehensive mixed-based data augmentation for detection of rice leaf disease in the wild

Rice (Oryza sativa L.) is one type of cultivated plant that has the ability to adapt to various conditions and is a main ingredient of food in many countries, especially in Asia, including Indonesia. Although rice can adapt to different environments, it's still susceptible to leaf diseases like brown spot, hispa, and blast. With current technological developments, machine learning is rapidly improving the efficiency of human work in various fields. Computer vision is one of the machine learning methods that is shown to be effective in performing image classification. The application of computer vision, especially through the Convolutional Neural Network (CNN) model, promises to be an effective solution. However, challenges arise in the wild rice plant dataset, where photographs are taken directly from rice fields. To overcome this, data augmentation techniques become important. Data augmentation not only overcomes overfitting but also helps the model understand diverse datasets. This research focuses on using data augmentation methods including Cutmix, Cutout, Mixup, FMix, and All Combination (Cutmix + Cutout + Mixup + FMix) to enhance the performance of the rice leaf detection model. From the test results, the mixed-based data augmentation method significantly improves the performance of the transfer learning model. All Combination method get the maximum accuracy of 91.51% when applied to ResNet34 on Setup Dataset and 99.75% when applied to MobileNetV3 on Wild Dataset. The proposed method can be combined with other methods to create a precise rice leaf disease detection system.

Diagnosis of Viral Diseases Using Deep Sequencing and Metagenomics Analyses.

Viruses are ubiquitous in nature and exist in a variety of habitats. The advancement in sequencing technologies has revolutionized the understanding of viral biodiversity associated with plant diseases. Deep sequencing combined with metagenomics is a powerful approach that has proven to be revolutionary in the last decade and involves the direct analysis of viral genomes present in a diseased tissue sample. This protocol describes the details of RNA extraction and purification from wild rice plant and their yield, RNA purity, and integrity assessment. As a final step, bioinformatics data analysis including demultiplexing, quality control, de novo transcriptome assembly, taxonomic allocation and read mapping following Illumina HiSeq small and total RNA sequencing are described. Furthermore, the total RNAs extraction protocol and an additional ribosomal rRNAs depletion step which are significantly important for viral genomes construction are provided.

Role of Thylakoid Protein Phosphorylation in Energy-Dependent Quenching of Chlorophyll Fluorescence in Rice Plants.

Under natural environments, light quality and quantity are extremely varied. To respond and acclimate to such changes, plants have developed a multiplicity of molecular regulatory mechanisms. Non-photochemical quenching of chlorophyll fluorescence (NPQ) and thylakoid protein phosphorylation are two mechanisms that protect vascular plants. To clarify the role of thylakoid protein phosphorylation in energy-dependent quenching of chlorophyll fluorescence (qE) in rice plants, we used a direct Western blot assay after BN-PAGE to detect all phosphoproteins by P-Thr antibody as well as by P-Lhcb1 and P-Lhcb2 antibodies. Isolated thylakoids in either the dark- or the light-adapted state from wild type (WT) and PsbS-KO rice plants were used for this approach to detect light-dependent interactions between PsbS, PSII, and LHCII proteins. We observed that the bands corresponding to the phosphorylated Lhcb1 and Lhcb2 as well as the other phosphorylated proteins were enhanced in the PsbS-KO mutant after illumination. The qE relaxation became slower in WT plants after 10 min HL treatment, which correlated with Lhcb1 and Lhcb2 protein phosphorylation in the LHCII trimers under the same experimental conditions. Thus, we concluded that light-induced phosphorylation of PSII core and Lhcb1/Lhcb2 proteins is enhanced in rice PsbS-KO plants which might be due to more reactive-oxygen-species production in this mutant.

RNA Sequencing Reveals Rice Genes Involved in Male Reproductive Development under Temperature Alteration.

Rice (Oryza sativa L.) is one of the most important food crops, providing food for nearly half of the world population. Rice grain yields are affected by temperature changes. Temperature stresses, both low and high, affect male reproductive development, resulting in yield reduction. Thermosensitive genic male sterility (TGMS) rice is sterile at high temperature and fertile at low temperature conditions, facilitating hybrid production, and is a good model to study effects of temperatures on male development. Semithin sections of the anthers of a TGMS rice line under low (fertile) and high (sterile) temperature conditions showed differences starting from the dyad stage, suggesting that genes involved in male development play a role during postmeiotic microspore development. Using RNA sequencing (RNA-Seq), transcriptional profiling of TGMS rice panicles at the dyad stage revealed 232 genes showing differential expression (DEGs) in a sterile, compared to a fertile, condition. Using qRT-PCR to study expression of 20 selected DEGs using panicles of TGMS and wild type rice plants grown under low and high temperature conditions, revealed that six out of the 20 selected genes may be unique to TGMS, while the other 14 genes showed common responses to temperatures in both TGMS and wild-type rice plants. The results presented here would be useful for further investigation into molecular mechanisms controlling TGMS and rice responses to temperature alteration.

Comparative assessment of multi-trait plant growth-promoting endophytes associated with cultivated and wild Oryza germplasm of Assam, India

This paper presents a comparative study of endophytic bacteria from cultivated (Oryza sativa) and wild rice (Oryza rufipogon) plants and their functional traits related to plant growth promotion. A total of 70 bacterial isolates were characterized by both biochemical and molecular identification methods. Taxonomic classification showed dominance of three major phyla, viz, Firmicutes (57.1%), Actinobacteria (20.0%) and Proteobacteria (22.8%). Screening for in vitro plant growth-promoting activities revealed a hitherto unreported endophytic bacterium from wild rice germplasm, Microbacterium laevaniformans RS0111 with highest indole acetic acid (28.39 ± 1.39µg/ml) and gibberellic acid (67.23 ± 1.83µg/ml) producing efficiency. Few other endophytic isolates from cultivated rice germplasm such as Bacillus tequilensis RHS01 showed highest phosphate solubilizing activity (81.70 ± 1.98µg/ml), while Microbacterium testaceum MKLS01 and Microbacterium enclense MI03 L05 showed highest potassium (53.42 ± 0.75µg/ml) and zinc solubilizing activity (157.50%). Fictibacillus aquaticus LP20 05 produced highest siderophore (64.8%). In vivo evaluation of plant growth-promoting efficiencies of the isolates showed that Microbacterium laevaniformans RS0111, Microbacterium testaceum MKLS01 and Bacillus tequilensis RHS 01 could increase rice grain yield by 3.4-fold when compared to the control group. This study indicates the potentiality of rice endophytes isolates as an effective bioinoculants.

Proteomic Analysis of Rice Subjected to Low Light Stress and Overexpression of OsGAPB Increases the Stress Tolerance

BackgroundLight provides the energy for photosynthesis and determines plant morphogenesis and development. Low light compromises photosynthetic efficiency and leads to crop yield loss. It remains unknown how rice responds to low light stress at a proteomic level.ResultsIn this study, the quantitative proteomic analysis with isobaric tags for relative and absolute quantitation (iTRAQ) was used and 1221 differentially expressed proteins (DEPs) were identified from wild type rice plants grown in control or low light condition (17% light intensity of control), respectively. Bioinformatic analysis of DEPs indicated low light remarkably affects the abundance of chloroplastic proteins. Specifically, the proteins involved in carbon fixation (Calvin cycle), electron transport, and ATPase complex are severely downregulated under low light. Furthermore, overexpression of the downregulated gene encoding rice β subunit of glyceraldehyde-3-phosphate dehydrogenase (OsGAPB), an enzyme in Calvin cycle, significantly increased the CO2 assimilation rate, chlorophyll content and fresh weight under low light conditions but have no obvious effect on rice growth and development under control light.ConclusionOur results revealed that low light stress on vegetative stage of rice inhibits photosynthesis possibly by decreasing the photosynthetic proteins and OsGAPB gene is a good candidate for manipulating rice tolerance to low light stress.

Mechanism of GA-mediated leaf sheath growth in rice: a proteomic approach

Gibberellins (GAs) mediated elongation growth and its associated proteomics in rice is relevant to crop productivity in many diversified ecological conditions. There is dearth of precise investigations conducted on proteome dynamics involved in leaf sheath elongation in both wild and mutant rice plants in response to GAs treatments. To explore the molecular mechanism of GA-induced leaf sheath elongation in rice, we conducted a comparative proteomics analysis of wild type rice and a GA biosynthesis deficient mutant osko2. The mutant displayed an obvious dwarfism phenotype, which could be dramatically rescued by application of exogenous GA3. The average levels of GAs in the dwarf mutant plants were lower than the wild type of rice. The proteomic analysis showed a total of 6352 proteins that were quantified, among which 688 differentially expressed proteins were identified as GA-responsive. The biological process classification indicated that metabolic process, cellular process and single-organism process related proteins were the dominant protein groups, and the differentially expressed proteins were largely located in chloroplast, cytoplasm, and nucleus and extracellular. Furthermore, these proteins were mainly involved in cell elongation, signal transduction, photosynthesis, and carbohydrate and protein metabolism. These results suggested that proteins involved in cell elongation, signal transduction and carbohydrate metabolism are regulated by GA in rice leaf-sheath growth.

Three new species of Tremellomycetes isolated from maize and northern wild rice.

The present work studied novel basidiomycetous yeasts from maize and northern wild rice plants. From comparisons of ribosomal internal transcribed spacer region (ITS) and large subunit (LSU) (D1 and D2 domains), and subsequent phylogenetic analyses, the following species were resolved and described: Papiliotrema zeae Yurkov & Kurtzman sp. nov. (ex-type cultures DSM 104035, NRRL Y-63980, MB 827356, GenBank MH718306), Solicoccozyma zizaniae Yurkov & Kurtzman sp. nov. (ex-type cultures DSM 104031, NRRL Y-7649, MB 827354, GenBank MH718302) and Vishniacozyma kurtzmanii Yurkov sp. nov. (ex-type cultures DSM 104032, NRRL Y-63981, MB 827355, GenBank MH718303). A search among environmental sequences showed that all three yeasts were previously detected, but not reliably assigned to a genus or clade. Papiliotrema zeae from maize and S. zizaniae from northern wild rice were previously found in agricultural soils under maize and rice, respectively.

Iron sulfide formation on root surfaces controlled by the life cycle of wild rice (Zizania palustris)

Iron sulfide plaques have been observed on roots of wild rice (Zizania palustris) and other wetland plants grown in sulfur-impacted freshwater ecosystems, but the mechanism of their formation and ramifications for plants have not been investigated. We exposed a model annual wetland plant, Zizania palustris, to elevated sulfate concentrations (3.1 mM) and quantified the development of iron oxide and iron sulfide precipitates on root surfaces throughout the plant life cycle. During the onset of seed production, root surfaces amended with sulfate transitioned within 1 week from iron (hydr)oxide plaques to iron sulfide plaques. During the same week, Fe(III) decreased on roots of plants not amended with sulfate but FeS did not accumulate. Prior to FeS accumulation, sulfate-amended plants had taken up the same amount of N as unamended plants. After FeS accumulation, total plant nitrogen did not increase further on sulfate-amended plants, indicating a cessation in nitrogen uptake, whereas total plant N continued to increase in unamended plants. Sulfate-amended plants produced fewer and lighter seeds with less nitrogen than unamended plants. FeS precipitation on roots may be associated with elevated sulfide and inhibited nitrogen uptake before the end of the plant’s life cycle, thus affecting the populations of this annual aquatic plant. We propose a mechanism by which a physiologically-induced decline in radial oxygen loss near the end of a plant’s life cycle initiates a precipitous decline in redox potential at the root surface and in adjacent porewater, initiating accumulation of iron sulfide plaques. These plaques could be an important locus for iron sulfide accumulation in wetland sediments.

Effects of sulfate and sulfide on the life cycle of Zizania palustris in hydroponic and mesocosm experiments.

Under oxygenated conditions, sulfate is relatively non-toxic to aquatic plants. However, in water-saturated soils, which are usually anoxic, sulfate can be reduced to toxic sulfide. Although the direct effects of sulfate and sulfide on the physiology of a few plant species have been studied in some detail, their cumulative effects on a plant's life cycle through inhibition of seed germination, seedling survival, growth, and seed production have been less well studied. We investigated the effect of sulfate and sulfide on the life cycle of wild rice (Zizania palustris L.) in hydroponic solutions and in outdoor mesocosms with sediment from a wild rice lake. In hydroponic solutions, sulfate had no effect on seed germination or juvenile seedling growth and development, but sulfide greatly reduced juvenile seedling growth and development at concentrations greater than 320μg/L. In outdoor mesocosms, sulfate additions to overlying water increased sulfide production in sediments. Wild rice seedling emergence, seedling survival, biomass growth, viable seed production, and seed mass all declined with sulfate additions and hence sulfide concentrations in sediment. These declines grew steeper during the course of the 5yr of the mesocosm experiment and wild rice populations became extinct in most tanks with concentrations of 250mg SO4 /L or greater in the overlying water. Iron sulfide precipitated on the roots of wild rice plants, especially at high sulfate application rates. These precipitates, or the encroachment of reducing conditions that they indicate, may impede nutrient uptake and be partly responsible for the reduced seed production and viability.

Non-invasive imaging of cellulose microfibril orientation within plant cell walls by polarized Raman microspectroscopy.

Cellulose microfibrils represent the major scaffold of plant cell walls. Different packing and orientation of the microfibrils at the microscopic scale determines the macroscopic properties of cell walls and thus affect their functions with a profound effect on plant survival. We developed a polarized Raman microspectroscopic method to determine cellulose microfibril orientation within rice plant cell walls. Employing an array of point measurements as well as area imaging and subsequent Matlab-assisted data processing, we were able to characterize the distribution of cellulose microfibril orientation in terms of director angle and anisotropy magnitude. Using this approach we detected differences between wild type rice plants and the rice brittle culm mutant, which shows a more disordered cellulose microfibril arrangement, and differences between different tissues of a wild type rice plant. This novel non-invasive Raman imaging approach allows for quantitative assessment of cellulose fiber orientation in cell walls of herbaceous plants, an important advancement in cell wall characterization.

De novo Transcriptome Assembly of Common Wild Rice (Oryza rufipogon Griff.) and Discovery of Drought-Response Genes in Root Tissue Based on Transcriptomic Data.

BackgroundThe perennial O. rufipogon (common wild rice), which is considered to be the ancestor of Asian cultivated rice species, contains many useful genetic resources, including drought resistance genes. However, few studies have identified the drought resistance and tissue-specific genes in common wild rice.ResultsIn this study, transcriptome sequencing libraries were constructed, including drought-treated roots (DR) and control leaves (CL) and roots (CR). Using Illumina sequencing technology, we generated 16.75 million bases of high-quality sequence data for common wild rice and conducted de novo assembly and annotation of genes without prior genome information. These reads were assembled into 119,332 unigenes with an average length of 715 bp. A total of 88,813 distinct sequences (74.42% of unigenes) significantly matched known genes in the NCBI NT database. Differentially expressed gene (DEG) analysis showed that 3617 genes were up-regulated and 4171 genes were down-regulated in the CR library compared with the CL library. Among the DEGs, 535 genes were expressed in roots but not in shoots. A similar comparison between the DR and CR libraries showed that 1393 genes were up-regulated and 315 genes were down-regulated in the DR library compared with the CR library. Finally, 37 genes that were specifically expressed in roots were screened after comparing the DEGs identified in the above-described analyses.ConclusionThis study provides a transcriptome sequence resource for common wild rice plants and establishes a digital gene expression profile of wild rice plants under drought conditions using the assembled transcriptome data as a reference. Several tissue-specific and drought-stress-related candidate genes were identified, representing a fully characterized transcriptome and providing a valuable resource for genetic and genomic studies in plants.

First Report of a Pythiogeton sp. Causing Root and Basal Stalk Rot of Wild Rice in California.

In the summer of 2012, an outbreak of a newly discovered root and basal stalk rot of wild rice (Zizania palustris L.) cv. Franklin was observed in a 16-ha field in Big Valley, Lassen County, California (GPS coordinates 41°08'41.93″ N 121°10'07.49″ W). Infected plants exhibiting rot and dieback of roots and stalks were in various stages of decline, including death. Symptomatic stem and root tissues from affected plants were surface disinfected in 1% NaOCl for 90 s and placed on PARP agar plates, which were then incubated at 25°C in the dark for 1 week. Hyphal tips were used to start and maintain the organism in pure cultures. Isolates were transferred into petri plates with water and sterilized blades of turfgrass for the production of hyphae and reproductive structures. Isolates had coenocytic hyphae and produced zoospores 20 to 30 μm in diameter outside of sporangia (75 to 160 × 46 to 110 μm) from a naked mass of protoplasm, unlike from a vesicle, which is characteristic of Pythium spp. (2). Based on these morphological features, the isolate was tentatively identified as a Pythiogeton sp. Total genomic DNA was extracted from mycelia using the DNeasy Plant Mini Kit (Qiagen Inc., Valencia, CA). The internal transcribed spacers (ITS) 1 and 2 flanking the 5.8S rRNA regions were amplified by PCR and sequenced using universal ITS5 and ITS4 primers. A BLAST search of the 855-bp sequences revealed 98% similarity with a sequence of P. ramosum isolate Pg-164 (GenBank Accession No. JQ610190.1). The 21 nucleotide differences suggest that the isolate from wild rice may be an unreported species. The sequences were submitted to GenBank (KF719169). To fulfill Koch's postulates and confirm pathogenicity, 100 wild rice seeds were surface disinfected in 1% NaOCl for 90 s and placed in a 500 ml sterile pot with 250 g of autoclaved sand. Three 5 mm-diameter disks from the margin of a 7-day-old culture growing on PARP were placed in each of five pots. As a control, three 5 mm-diameter disks from a non-inoculated PARP plate were placed in five different pots, and five pots with autoclaved sand were not inoculated. All pots were kept in a randomized complete block design at 25°C for 14 days under a 14-h photoperiod. The pathogenicity test was repeated three times. After 14 days, the inoculated plants in all tests developed root and basal stalk rot, consistent with the symptoms observed on diseased wild rice in the field. The Pythiogeton sp. was consistently re-isolated on PARP from symptomatic plants but not from control plants. The non-inoculated wild rice plants remained asymptomatic. DNA sequences of the ITS region of the re-isolated Pythiogeton sp. revealed 100% identity with the isolate from the field. There have been reports of P. zeae on corn in Korea and P. zizaniae on water bamboo in Taiwan (1,2,3). This is the first report of a Pythiogeton sp. on wild rice.

Change of Photosynthetic Gas Exchange and Chlorophyll Fluorescence of Cd-Sensitive Mutant Rice in Response to Cd Stress

The growth, photosynthetic gas exchange and chlorophyll fluorescence were investigated in wild type and mutant rice plants treated with 50 μmol L-1 Cd. The results showed that plant height, dry mass, and chlorophyll content decreased by Cd treatment, and the mutant showed more severe reduction than wild type rice. Net photosynthetic rate (Pn), transpiration rate (E), stomatal conductance (Gs), maximal photochemical efficiency of PSII (Fv/Fm), effective PSII quantum yield (ΦPS2), and photochemical quenching (qP) were decreased and intercellular CO2 concentration (Ci) and and non-photochemical quenching (qN) were enhanced in Cd-treated plants with the increasing of Cd exposure time, with changes in the mutant being more evident. The results suggest that Cd inhibits photosynthesis due to non-stomatal limitations and the response of PSII reaction centre and the mutant has less capacity of acclimation to Cd stress.

Functional Analysis of Pid3-A4, an Ortholog of Rice Blast Resistance Gene Pid3 Revealed by Allele Mining in Common Wild Rice

The rice blast resistance gene Pid3 encodes a nucleotide-binding-site leucine-rich repeat (NBS-LRR) protein. This gene was cloned from the rice 'Digu' (indica) by performing a genome-wide comparison of the NBS-LRR gene family between two genome-sequenced varieties, '9311' (indica) and 'Nipponbare' (japonica). In this study, we performed functional analysis of Pid3-A4, an ortholog of Pid3 revealed by allele mining in the common wild rice A4 (Oryza rufipogon). The predicted protein encoded by Pid3-A4 shares 99.03% sequence identity with Pid3, with only nine amino-acid substitutions. In wild rice plants, Pid3-A4 is constitutively expressed, and its expression is not induced by Magnaporthe oryzae isolate Zhong-10-8-14 infection. Importantly, in transgenic plants, Pid3-A4, as compared with Pid3, displays a distinct resistance spectrum to a set of M. oryzae isolates, including those that prevail in the rice fields of Sichuan Province. Therefore, Pid3-A4 should be quite useful for the breeding of rice blast resistance, especially in southwestern China.

Ectopic expression of ubiquitin-conjugating enzyme gene from wild rice, OgUBC1, confers resistance against UV-B radiation and Botrytis infection in Arabidopsis thaliana

A previously unidentified gene encoding ubiquitin-conjugating enzyme was isolated from leaves of wild rice plant treated with wounding and microbe-associated molecular patterns. The OgUBC1 gene was composed of 148 amino acids and contained a typical active site and 21 ubiquitin thioester intermediate interaction residues and 4 E3 interaction residues. Both exogenous application of salicylic acid and UV-B irradiation triggered expression of OgUBC1 in leaves of wild rice. Recombinant OgUBC1 proteins bound to ubiquitins in vitro, proposing that the protein might act as E2 enzyme in planta. Heterologous expression of the OgUBC1 in Arabidopsis thaliana protected plants from cellular damage caused by an excess of UV-B radiation. A stable expression of chalcone synthase gene was detected in leaves of OgUBC1-expressing Arabidopsis, resulting in producing higher amounts of anthocyanin than those in wild-type Col-0 plants. Additionally, both pathogenesis-related gene1 and 5 were transcribed in the transgenic Arabidopsis in the absence of pathogen infection. The OgUBC1-expressing plants were resistant to the infection of Botrytis cinerea. Taken together, we suggested that the OgUBC1 is involved in ubiquitination process important for cellular response against biotic and abiotic stresses in plants.