Oryza Rufipogon Research Articles

Studies on the cold tolerance of ratoon \u2018Chaling\u2019 common wild rice

BackgroundRice is the staple food of many people around the world. However, most rice varieties, especially widely grown indica varieties and hybrids, are sensitive to cold stress. In order to provide a basis for the utilization of a common wild rice (CWR, Oryza rufipogon Griff.) named ‘Chaling’ CWR in cold-tolerant rice breeding and deepen the understanding of rice cold tolerance, the cold tolerance of ratoon ‘Chaling’ CWR was studied under the stress of the natural low temperature in winter in Changsha, Hunan province, China, especially under the stress of abnormal natural low temperature in Changsha in 2008, taking other ratoon CWR accessions and ratoon cultivated rice phenotypes as control.ResultsThe results showed that ratoon ‘Chaling’ CWR can safely overwinter under the natural conditions in Changsha (28° 22′ N), Hunan province, China, which is a further and colder northern place than its habitat, even if it suffers a long-term low temperature stress with ice and snow. In 2008, an extremely cold winter appeared in Changsha, i.e., the average daily mean temperature of 22 consecutive days from January 13 to February 3 was − 1.0 °C, and the extreme low temperature was − 4.7 °C. After subjected to this long-term cold stress, the overwinter survival rate of ratoon ‘Chaling’ CWR was 100%, equals to that of ratoon ‘Dongxiang’ CWR which is northernmost distribution in the word among wild rice populations, higher than those of ratoon ‘Fusui’ CWR, ratoon ‘Jiangyong’ CWR, and ratoon ‘Liujiang’ CWR (63.55–83.5%) as well as those of ratoon ‘Hainan’ CWR, ratoon ‘Hepu’ CWR, and all the ratoon cultivated rice phenotypes including 3 japonica ones, 3 javanica ones, and 5 indica ones (0.0%).ConclusionsThe results indicate that ratoon ‘Chaling’ CWR possesses strong cold tolerance and certain freezing tolerance.

Molecular and Morphological Divergence of Australian Wild Rice.

Two types of perennial wild rice, Australian Oryza rufipogon and a new taxon Jpn2 have been observed in Australia in addition to the annual species Oryza meridionalis. Jpn2 is distinct owing to its larger spikelet size but shares O. meridionalis-like morphological features including a high density of bristle cells on the awn surface. All the morphological traits resemble O. meridionalis except for the larger spikelet size. Because Jpn2 has distinct cytoplasmic genomes, including the chloroplast (cp), cp insertion/deletion/simple sequence repeats were designed to establish marker systems to distinguish wild rice in Australia in different natural populations. It was shown that the new taxon is distinct from Asian O. rufipogon but instead resembles O. meridionalis. In addition, higher diversity was detected in north-eastern Australia. Reproductive barriers among species and Jpn2 tested by cross-hybridization suggested a unique biological relationship of Jpn2 with other species. Insertions of retrotransposable elements in the Jpn2 genome were extracted from raw reads generated using next-generation sequencing. Jpn2 tended to share insertions with other O. meridionalis accessions and with Australian O. rufipogon accessions in particular cases, but not Asian O. rufipogon except for two insertions. One insertion was restricted to Jpn2 in Australia and shared with some O. rufipogon in Thailand.

Nutritional values of swamp grasses as feed for Pampangan Buffaloes in South Sumatra, Indonesia

Abstract. Muhakka, Suwignyo RA, Budianta D, Yakup. 2020. Nutritional values of swamp grasses as feed for Pampangan Buffaloes in South Sumatra, Indonesia. Biodiversitas 21: 953-961. This study was aimed at determining the types and quality of vegetation in the swamp area, which could be used as sources of roughage for Pampangan buffaloes in South Sumatra. In this descriptive study, Results showed that the highest crude protein and ether extract contents, 20.56 and 2.92%, respectively, were found in (Neptunia oleracea). The highest ash content of 25.19% was found in Cyperus digitatus. The lowest fiber content (11.01%) was found in Ludwigia hyssopifolia, which also had the lowest content of Neutral Detergent Fiber (NDF) (40.64%). Hemicellulose content was found to be highest (37.14%) in Leersia hexandra. The lowest ADF (23.66%) and lignin (14,84%) contents were found in Nymphaea lotus. N. oleracea was found to have the lowest content (27.08%) of cellulose. It was concluded that the swamp vegetation found in this study consisted of 17 species of grasses and herbs (89.47%) and two species of legumes (10.53%). C. digitatus and L. hyssopifolia were found to have the best nutritional values. Dominant and palatable vegetation with good nutritional values, which were potential to be used as sources of roughage for Pampangan buffaloes, were Hymenachne acutigluma, Oryza rufipogon, Hymenachne amplexicaulis, Polygonum barbatum, and Eleocharis dulcis.

Fine mapping of the qHTB1-1QTL, which confers heat tolerance at the booting stage, using an Oryza rufipogon Griff. introgression line.

The qHTB1-1 QTL, controlling heat tolerance at the booting stage in rice, was fine mapped to a 47.1kb region containing eight candidate genes. Two positional candidate genes showed significant changes in expression levels under heat stress. High-temperature stress at the booting stage has the potential to significantly limit rice production. An interspecific advanced backcrossed population between the Oryza sativa L. cultivar R53 and the wild Oryza rufipogon Griff accession HHT4 was used as the source material to develop a set of chromosome segment introgression lines to elucidate the genetic mechanism of the qHTB1-1 QTL in heat tolerance. A single-chromosome-segment introgression line, IL01-15, was used to develop secondary populations for the mapping of qHTB1-1 on chromosome 1 for heat tolerance at the booting stage. Using the BC5F2, BC5F3, and BC5F4 populations, we first confirmed qHTB1-1 and validated the phenotypic effect. The qHTB1-1 QTL explained 13.1%, 16.9%, and 17.8% of the phenotypic variance observed in the BC5F2, BC5F3, and BC5F4 generations, respectively. Using homozygous recombinants screened from larger BC6F2 and BC6F3 populations, qHTB1-1 was fine mapped within a 47.1kb region between markers RM11633 and RM11642. Eight putative predicted genes were annotated in the region, and six genes were predicted to encode expressed proteins. The expression patterns of these six genes demonstrated that LOC_Os01g53160 and LOC_Os01g53220 were highly induced by heat stress in IL01-15 compared to R53. Sequence comparison of the gene-coding regions of LOC_Os01g53160 and LOC_Os01g53220 between R53 and IL01-15 revealed one synonymous and two nonsynonymous SNPs in exons, respectively. Our results provide a basis for identifying the genes underlying qHTB1-1 and indicate that markers linked to the qHTB1-1 locus can be used to improve the heat tolerance of rice at the booting stage by marker-assisted selection.

A common wild rice-derived BOC1 allele reduces callus browning in indica rice transformation

Callus browning, a common trait derived from the indica rice cultivar (Oryza sativa L.), is a challenge to transformation regeneration. Here, we report the map-based cloning of BROWNING OF CALLUS1 (BOC1) using a population derived from crossing Teqing, an elite indica subspecies exhibiting callus browning, and Yuanjiang, a common wild rice accession (Oryza rufipogon Griff.) that is less susceptible to callus browning. We show that BOC1 encodes a SIMILAR TO RADICAL-INDUCED CELL DEATH ONE (SRO) protein. Callus browning can be reduced by appropriate upregulation of BOC1, which consequently improves the genetic transformation efficiency. The presence of a Tourist-like miniature inverted-repeat transposable element (Tourist MITE) specific to wild rice in the promoter of BOC1 increases the expression of BOC1 in callus. BOC1 may decrease cell senescence and death caused by oxidative stress. Our study provides a gene target for improving tissue culturability and genetic transformation.

Rice Germplasm: Source of Iron and Zinc for Nutritional Security

Rice is the most important food crop, more than half (½) of the world’s population depends on it for their sustainable livelihood. Population growth is increasing day by day and it will reach more than > 9 billion by 2050, and to feed the overpopulation we need to produce nearly double amount of food grains to fulfil the demand. It was projected that Global rice yields and consumption rate will rise by 12% and 13% respectively by the year 2027 (FAO 2018). The Green Revolution has played a prime role in the 1960s -1970s to increase agricultural productivity worldwide to make many countries in food self-sufficiency leading to food secured world. The present situation is posing serious challenge for global food security in coming decades due to climate change, limited availability of arable land and water, more over other natural resources are continued to exhaustion. Rice is consumed as sole source of energy mainly in South and Southeast Asia, Africa, and Latin America which causes micronutrients deficiency leading to chronic malnutrition. Malnutrition due to inadequate intake of micronutrients mostly iron and zinc can lead to ‘Hidden Hunger’, which is responsible for many diseases. Important micronutrients Fe and Zn deficiencies in rice promoting the hidden hunger and causes anemia, stunted growth, poor cognitive development for iron deficiency and for zinc deficiency that causes reduced immunity, diarrhea, lesions on skin, mental lethargy. Approximately 2 billion people are suffering from malnutrition deficiencies for iron and zinc. Micronutrient elements Fe and Zn are available in various local rice varieties which ranged from 6.3-24.4 mg/kg Fe and 13.53- 58.4 mg/kg Zn. Biofortification of rice can assist to alleviate malnutrition associated diseases among the poor people those who are depended on rice as staple food for 40-70% daily caloric intake. Nutritional studies recommended that 24–28 mg/ kg Zn and 13 mg/ kg Fe concentration in polished grain is vital to attain the 30% of human estimated average requirement. Biofortification of cereal foods through conventional breeding can be a good opportunity to improve micronutrient deficiency in the diets. Wild rice accessions (Oryza rufipogon, O.nivara, O. latifolia and O. officinalis) may be used to improve the mineral nutrition in rice grain through breeding and conserve as important resources.

Systematic Characterization of Long Non-Coding RNAs and Their Responses to Drought Stress in Dongxiang Wild Rice

Long non-coding RNAs (lncRNAs) play important roles in response to various biotic and abiotic stresses. So far, systematic identification and characterization of lncRNAs have been reported in a few model plant species and major crops, but their roles in abiotic stress response have not yet been reported in common wild rice (Oryza rufipogon). Dongxiang wild rice (DXWR) possesses a high degree of drought resistance and has been well recognized as a precious genetic resource for drought resistant rice breeding. We presented the reference catalog of 1 655 novel lncRNA transcripts in DXWR using strand-specific RNA sequencing and bioinformatics approaches. Meanwhile, a total of 1 092 lncRNAs were determined as differentially expressed lncRNAs under drought stress. Quantitative real-time PCR results exhibited a high concordance with RNA sequencing data, which confirmed that the expression patterns of lncRNAs based on RNA sequencing were highly reliable. Furthermore, 8 711 transcripts were predicted as target genes of the differentially expressed lncRNAs. Functional annotation analysis based on Gene Ontology and Kyoto Encyclopedia of Genes and Genomes databases showed that the target genes were significantly enriched in cellular and metabolic processes, cell part, binding and plant hormone signal transduction, as well as many other terms related to abiotic stress resistance. These results expanded our understanding of lncRNA biology and provided candidate regulators for genetic improvement of drought resistance in rice cultivars.

Natural variation in the expression and catalytic activity of a naringenin 7‐O‐methyltransferase influences antifungal defenses in diverse rice cultivars

Phytoalexins play a pivotal role in plant-pathogen interactions. Whereas leaves of rice (Oryza sativa) cultivar Nipponbare predominantly accumulated the phytoalexin sakuranetin after jasmonic acid induction, only very low amounts accumulated in the Kasalath cultivar. Sakuranetin is synthesized from naringenin by naringenin 7-O-methyltransferase (NOMT). Analysis of chromosome segment substitution lines and backcrossed inbred lines suggested that NOMT is the underlying cause of differential phytoalexin accumulation between Nipponbare and Kasalath. Indeed, both NOMT expression and NOMT enzymatic activity are lower in Kasalath than in Nipponbare. We identified a proline to threonine substitution in Kasalath relative to Nipponbare NOMT as the main cause of the lower enzymatic activity. Expanding this analysis to rice cultivars with varying amounts of sakuranetin collected from around the world showed that NOMT induction is correlated with sakuranetin accumulation. In bioassays with Pyricularia oryzae, Gibberella fujikuroi, Bipolaris oryzae, Burkholderia glumae, Xanthomonas oryzae, Erwinia chrysanthemi, Pseudomonas syringae, and Acidovorax avenae, naringenin was more effective against bacterial pathogens and sakuranetin was more effective against fungal pathogens. Therefore, the relative amounts of naringenin and sakuranetin may provide protection against specific pathogen profiles in different rice-growing environments. In a dendrogram of NOMT genes, those from low-sakuranetin-accumulating cultivars formed at least two clusters, only one of which involves the proline to threonine mutation, suggesting that the low sakuranetin chemotype was acquired more than once in cultivated rice. Strains of the wild rice species Oryza rufipogon also exhibited differential sakuranetin accumulation, indicating that this metabolic diversity predates rice domestication.

Analysis on fertility and inheritance of hybrid male sterility of indica rice 9814HS-1

Hybrid rice has generally a yield-increasing heterosis of 10%−15% compared with inbred parents. Food and Agriculture Organization (FAO) has recommended hybrid rice as one of the best choices for solving the food shortage in the developing countries. Male sterility provides a basic genetic tool for hybrid rice breeding. Hybrid male sterility refers to the phenomenon that F1 hybrid from two parents is abnormal or nonfunctional in the development of male organs. A new germplasm source of hybrid male sterility is valuable for establishing a novel system for using heterosis by hybrid breeding of three-way crossing, which helps to develop elite hybrid rice with better comprehensive traits. To date, hybrid male sterility occurs commonly from the crosses between species (e.g. Oryza rufipogon × Oryza sativa ) or subspecies (e.g. indica rice × japonica rice). Nevertheless, it is not clear if the hybrid male sterility could be induced from a cross within a subspecies. Here, we reported firstly the hybrid male sterility resulted from a cross between two indica rice parents, i.e., two WA-type maintainer lines of indica rice T98B and M114B. The InDel marker analysis showed that T98B and M114B had an indica -genotype frequency at 0.94 and 1.00, respectively, indicating both of them belong to indica rice. Field observation showed that 9814HS-1, the F1 hybrid of T98B (as female parent) and M114B (as male parent), was eco-typically male sterile. The pollens of 9814HS-1 were completely aborted, resulting in a seed setting rate at 0.00% when heading after early October at Changsha or before mid-March at Sanya, while both parents T98B and M114B were normally fertile under the same conditions. Interestingly, when T98B and M114B were crossed with eight other indica rice varieties, all of their F1 hybrids were normally fertile with a seed setting rate ranged from 80.35% to 91.87%, implying that the hybrid male sterility of 9814HS-1 is induced from the specific parental incompatibility between T98B and M114B. The restorability test showed that 9814HS-1 could be restored for fertility by all of six representative indica rice lines, with seed setting rates ranged from 85.24% to 93.21% in their F1 hybrids, indicating that the broad spectrum of restorability of 9814HS-1. This male sterility provides a good basis for hybrid breeding of three-way cross. Genetic analysis showed that both of the F1 hybrid and its reciprocal cross from T98B and M114B were male sterile, suggesting the hybrid male sterility was controlled by nuclear genes. The Chi-square test supported that the separation ratio of sterile: Fertile plants in both F2 and BC1F1 populations was confirmed to be 1:3, which we infer that the hybrid male sterility in 9814HS-1 is controlled by two pairs of non-allelic nuclear genes and occurs only when they are in a heterozygous state. This study provides a new perspective for re-recognizing rice reproductive barriers and opens up a new way for the multiple-line hybrid rice breeding.

Construction of chromosome segment substitution lines of Dongxiang common wild rice (Oryza rufipogon Griff.) in the background of the japonica rice cultivar Nipponbare (Oryza sativa L.)

Dongxiang common wild rice (Oryza rufipogon Griff.) is believed to have the northernmost distribution of any wild rice species. Many favorable genes were lost during rice domestication, and Dongxiang common wild rice is a potential source of many genes related to biological and abiotic stress resistance and high grain yield. Despite its importance, japonica rice has not yet been used as a background material for the construction of introgression lines carrying Dongxiang common wild rice chromosome segments. In this study, we used Dongxiang common wild rice as the donor parent and Nipponbare (Oryza sativa L), a reference-sequence japonica cultivar, as the recurrent parent to develop a set of 104 chromosome segment substitution lines (CSSLs) through crossing and backcrossing with marker-assisted selection based on 203 polymorphic molecular markers evenly distributed across 12 chromosomes. The 104 CSSLs covered 87.94% of the genome of Dongxiang common wild rice. Each CSSL contained an average of four introgressed segments, and the average segment length was 3.3 Mb. Quantitative trait locus (QTL) analysis of the panicle-related traits of the CSSLs at two sites (Beijing and Nanchang, Jiangxi Province) revealed 18 QTLs for eight traits. Among these 18 QTLs were two known grain length- and width-related genes and four novel QTLs. In addition, two QTLs were verified, and two novel QTLs were identified, for panicle neck length, a domestication-related trait. The developed CSSLs potentially represent a valuable population for detecting favorable genes in common wild rice and creating germplasm resources for japonica rice breeding.

QTL analysis for awnlessness using a backcross population between Oryza rufipogon and O. sativa IR36

QTL analysis for awnlessness using a backcross population between Oryza rufipogon and O. sativa IR36

The evolution study on Oryza rufipogon. dw by whole-genome sequencing

The species of Oryza rufipogon. dw was first discovered at Dongxiang, Jiangxi in 1978. It is recognized as abundant in genetic resources with the characteristics of cold and insect resistance. A total of 100.15 Gb raw data was obtained from seven pair-end libraries by Illumina Hiseq4000 platform. Subsequently, a draft assembly genome of O. rufipogon. dw was generated with a final size of 422.7 Mb with a contig N50 of 15 kb and a scaffold N50 of 296.2 bb. The assembly genome size was higher than the estimated genome size (413 Mb) based on k-mer analysis. The identified repeat sequences accounted for 40.09% of the entire genome, and 32,521 protein-coding genes with an average of 4.59 exons per gene was annotated in five databases. Phylogenetic analysis using 1460 single-copy gene, O. rufipogon. dw was close with O. rufipogon by Bayes method. The wild rice species of O. rufipogon. dw divergence was estimated at ∼0.3 million years ago (Mya) from O. rufipogon, and ∼0.6 Mya from the O. sativa. The draft genome of O. rufipogon. dw provided an essential resource for its origin and evolution study.

Bulliform Phytolith Size of Rice and Its Correlation With Hydrothermal Environment: A Preliminary Morphological Study on Species in Southern China.

In the last decade, our understanding of rice domestication has improved by new archaeological findings using advanced analytical techniques such as morphological and morphometric analyses on rice grains, spikelet bases and phytoliths, and ancient DNA analysis on rice remains. Previous studies have considered the size of rice bulliform phytoliths as a proxy for tracking the domestication process. These phytoliths are often abundant and well preserved in sediments, and their shape is under the control of numerous genes, which may shift toward larger sizes by genetic mutation in domestication. Therefore, it has been assumed that the bulliforms of domesticated rice are usually larger than those of wild ones; however, morphometric data supporting this assumption are lacking in the literature, thereby requiring additional evidence to test its veracity. In this study, the vertical and horizonal lengths of bulliform phytoliths were measured in four rice species (domesticated Oryza sativa and wild Oryza rufipogon, Oryza officinalis, and Oryza meyeriana) from different regions of southern China. We found that the bulliform morphometric data of wild and domesticated rice overlapped and that there was no statistically significant difference between them. Therefore, bulliform size could not be used as a diagnostic indicator to distinguish domesticated rice from wild species and is a supporting rather than conclusive proxy for determining the domesticated status of rice in archaeological research. We further found that larger rice bulliform sizes likely occurred at the locations with higher temperature, precipitation, and water levels, indicating hydrothermal environment is an alternative factor influencing the size of rice bulliform phytoliths. For further archaeological use of an increasing size trend of bulliform phytoliths to reveal the process of rice domestication, we present some suggestions for controlling the influence of hydrothermal factors. Even so, the combination of bulliform phytolith size with other established criteria is strongly suggested to provide precise identification of wild and domesticated rice in future research.

Signatures of differential selection in chloroplast genome between japonica and indica

BackgroundThe domestication process of Asian rice (Oryza sativa L.) is complicated. It’s well established that Oryza rufipogon is the ancestor of Asian rice, although the number of domestication events still controversial. Recently, numerous types of studies based on rice nuclear genome have been conducted, but the results are quite different. Chloroplasts (cp) are also part of the rice genome and have a conserved cyclic structure that is valuable for plant genetics and evolutionary studies. Therefore, we conducted chloroplast-based studies, aiming to provide more evidence for the domestication of Asian rice.ResultsA total of 1389 variants were detected from the chloroplast genomes of 412 accessions obtained through the world. Oryza sativa L. ssp. japonica exhibited slightly less diversity (π) than Oryza sativa L. indica and wild rice. The fixation index values (FST) revealed that indica and japonica exhibited farther genetic distances compared with wild rice. Across cp genome, Tajima’s D test demonstrated that different selection sites occurred in Asian rice. Principal component analyses (PCA) and multidimensional scaling (MDS) clearly classify the Asian rice into different groups. Furthermore, introgression patterns identified that indica and japonica shared no introgression events in cp level, and phylogenetic studies showed cultivated rice were well separated from different type of wild rice.ConclusionsHere, we focus on the domestication of Asian rice (indica and japonica). Diversity and phylogenetic analyses revealed some selection characteristics in the chloroplast genome that potentially occurred in different Asian rice during the domestication. The results shown that Asian rice had been domesticated at least twice. In additional, japonica may experience a strong positive selection or bottleneck event during the domestication.

Variation of diterpenoid phytoalexin oryzalexin A production in cultivated and wild rice

Rice (Oryza sativa) leaves accumulate phytoalexins in response to pathogen attack. The major phytoalexins in rice are diterpenoids such as oryzalexins, momilactones, and phytocassanes. We measured the amount of oryzalexin A in leaves irradiated by UV light, treated with jasmonic acid, or inoculated with conidia of Bipolaris oryzae in the japonica cultivar Nipponbare and the indica cultivar Kasalath. Nipponbare leaves accumulated oryzalexin A at a high concentration, but Kasalath leaves did not. The locus responsible for this difference was mapped using backcrossed inbred lines and chromosome substitution lines. A region on Chr. 12 containing the KSL10 gene was responsible for the deficiency in oryzalexin A in the Kasalath cultivar. The amount of KSL10 transcript increased in Nipponbare leaves but not in Kasalath leaves in response to UV light irradiation, indicating that the suppressed expression of KSL10 caused the deficiency of oryzalexin A in Kasalath. We analyzed oryzalexin A accumulation in UV light-irradiated leaves of cultivars in the world rice core collection. There were cultivars that accumulated oryzalexin A and those that did not, and both of these chemotypes were found in japonica and indica subspecies. Furthermore, these chemotypes were found in the wild rice species Oryza rufipogon. The phylogenetic relationship of KSL10 sequences was not correlated to oryzalexin A chemotypes. These findings suggested that the biosynthesis of oryzalexin A was acquired by a common ancestor of O. rufipogon and was lost multiple times during the evolutionary process.

Sugar Transporter Proteins (STPs) in Gramineae Crops: Comparative Analysis, Phylogeny, Evolution, and Expression Profiling.

Sugar transporter proteins (STPs), such as H+/sugar symporters, play essential roles in plants’ sugar transport, growth, and development, and possess an important potential to enhance plants’ performance of multiple agronomic traits, especially crop yield and stress tolerance. However, the evolutionary dynamics of this important gene family in Gramineae crops are still not well-documented and functional differentiation of rice STP genes remain unclear. To address this gap, we conducted a comparative genomic study of STP genes in seven representative Gramineae crops, which are Brachypodium distachyon (Bd), Hordeum vulgare (Hv), Setaria italica (Si), Sorghum bicolor (Sb), Zea mays (Zm), Oryza rufipogon (Or), and Oryza sativa ssp. japonica (Os). In this case, a total of 177 STP genes were identified and grouped into four clades. Of four clades, the Clade I, Clade III, and Clade IV showed an observable number expansion compared to Clade II. Our results of identified duplication events and divergence time of duplicate gene pairs indicated that tandem, Whole genome duplication (WGD)/segmental duplication events play crucial roles in the STP gene family expansion of some Gramineae crops (expect for Hv) during a long-term evolutionary process. However, expansion mechanisms of the STP gene family among the tested species were different. Further selective force studies revealed that the STP gene family in Gramineae crops was under purifying selective forces and different clades and orthologous groups with different selective forces. Furthermore, expression analysis showed that rice STP genes play important roles not only in flower organs development but also under various abiotic stresses (cold, high-temperature, and submergence stresses), blast infection, and wounding. The current study highlighted the expansion and evolutionary patterns of the STP gene family in Gramineae genomes and provided some important messages for the future functional analysis of Gramineae crop STP genes.

Fine Mapping of a Low-Temperature Germinability QTLqLTG1Using Introgression Lines Derived fromOryza rufipogon

Low-temperature germinability (LTG) is an important trait for rice direct seeding at temperate and high-altitude region. Previously, five QTLs (quantitative trait loci) for LTG were detected using an interspecific cross population between the Korea japonica cultivar Hwaseong and Oryza rufipogon (IRGSP#105491). O. rufipogon alleles at all loci increased the germination rate at the 13℃ condition. In this study, we tried to confirm and fine-map qLTG1 located on the short arm of chromosome 1. To map the qLTG1, two introgression lines, TR5 and TR20 were crossed to Hwaseong to develop F2:3 populations. QTL analysis confirmed the existence of the qLTG1 and it explained 55.5% and 29.9% of phenotypic variation in two populations, respectively. Substitution mapping using informative recombinant lines indicated that qLTG1 was located in 167-kb region between two SSR markers RM10310 and RM10326. This segment harbored 18 genes with nine of them were annotated with specific gene function. In addition, the O. rufipogon introgression in this region was associated with an increase in spikelets per panicle in the Hwaseong background. The results strongly indicate that the O. rufipogon alleles will be a valuable source of genes in improving japonica rice for low-temperature germinability and yield. To our knowledge, this is the first report to fine-map qLTG1 associated with LTG in rice considering that no QTL for LTG has not been reported near this QTL region from other biparental populations.

Development of a drought stress-resistant rice restorer line through Oryza sativa–rufipogon hybridization

Restorer line F6 (Oryza sativa L. ssp. indica) has been widely used in hybrid rice breeding systems in southern China. However, line F6 is susceptible to drought stress, which restricts its utilization in many areas. Dongxiang wild rice (DXWR, Oryza rufipogon Griff.) has strong drought stress resistance, but the molecular factors responsible for drought resistance in DXWR remain unknown. In this study, we used the combination of phenotypic selection and molecular marker-assisted selection (MAS) to improve the drought stress resistance of line F6 by introgression of qSDT12-2, a large effect drought stress-related quantitative trait locus identified in DXWR. Molecular MAS was carried out using linked marker RM1226, which is associated with qSDT12-2. Genomic background assessmentwas performed using 112 polymorphic markers. Finally, a stable drought stress-resistant backcross inbred line (BIL) was developed from a BC5F5 population, termed BIL627. Genetic constitution analysis revealed that the genome of BIL627 is almost identical (99.1%) to that of the restorer line F6. Further, BIL627 showed no yield penalty and no decrease in restorationability under normal conditions. Taken together, our findings reveal the intrinsic value of using genetic resources present in wild species of Oryza to improve undesirable traits found in cultivated rice.

Expansion and Evolutionary Patterns of Glycosyltransferase Family 8 in Gramineae Crop Genomes and Their Expression under Salt and Cold Stresses in Oryza sativa ssp. japonica.

Plant cell walls play a fundamental role in several ways, providing structural support for cells, resistance against pathogens and facilitating the communication between cells. The glycosyltransferase family 8 (GT8) is involved in the formation of the plant cell wall. However, the evolutionary relationship and the functional differentiation of this important gene family remain obscure in Gramineae crop genomes. In the present investigation, we identified 269 GT8 genes in the seven Gramineae representative crop genomes, namely, 33 in Hordeum vulgare, 37 in Brachypodium distachyon, 40 in Oryza sativa ssp. japonica, 41 in Oryza rufipogon, 36 in Setaria italica, 37 in Sorghum bicolor, and 45 in Zea mays. Phylogenetic analysis suggested that all identified GT8 proteins belonged to seven subfamilies: galacturonosyltransferase (GAUT), galacturonosyltransferase-like (GATL), GATL-related (GATR), galactinol synthase (GolS), and plant glycogenin-like starch initiation proteins A (PGSIP-A), PGSIP-B, and PGSIP-C. We estimated that the GAUT subfamily might be further divided into four subgroups (I–IV) due to differentiation of gene structures and expression patterns. Our orthogroup analysis identified 22 orthogroups with different sizes. Of these orthogroups, several orthogroups were lost in some species, such as S. italica and Z. mays. Moreover, lots of duplicate pairs and collinear pairs were discovered among these species. These results indicated that multiple duplication modes led to the expansion of this important gene family and unequal loss of orthogroups and subfamilies might have happened during the evolutionary process. RNA-seq, microarray analysis, and qRT-PCR analyses indicated that GT8 genes are critical for plant growth and development, and for stresses responses. We found that OsGolS1 was significantly up-regulated under salt stress, while OsGAUT21, OsGATL2, and OsGATL5 had remarkable up-regulation under cold stress. The current study highlighted the expansion and evolutionary patterns of the GT8 gene family in these seven Gramineae crop genomes and provided potential candidate genes for future salt- and cold- resistant molecular breeding studies in O. sativa.

Comparative study of the mycorrhizal root transcriptomes of wild and cultivated rice in response to the pathogen Magnaporthe oryzae

BackgroundRice, which serves as a staple food for more than half of the world’s population, is very susceptible to the pathogenic fungus, Magnaporthe oryzae. However, common wild rice (Oryza rufipogon), which is the ancestor of Asian cultivated rice (O. sativa), has significant potential as a genetic source of resistance to M. oryzae. Recent studies have shown that the domestication of rice has altered its relationship to symbiotic arbuscular mycorrhizae. A comparative response of wild and domestic rice inhabited by mycorrhizae to infection by M. oryzae has not been documented.ResultsIn the current study, roots of wild and cultivated rice colonized with the arbuscular mycorrhizal (AM) fungus (AMF) Rhizoglomus intraradices were used to compare the transcriptomic responses of the two species to infection by M. oryzae. Phenotypic analysis indicated that the colonization of wild and cultivated rice with R. intraradices improved the resistance of both genotypes to M. oryzae. Wild AM rice, however, was more resistant to M. oryzae than the cultivated AM rice, as well as nonmycorrhizal roots of wild rice. Transcriptome analysis indicated that the mechanisms regulating the responses of wild and cultivated AM rice to M. oryzae invasion were significantly different. The expression of a greater number of genes was changed in wild AM rice than in cultivated AM rice in response to the pathogen. Both wild and cultivated AM rice exhibited a shared response to M. oryzae which included genes related to the auxin and salicylic acid pathways; all of these play important roles in pathogenesis-related protein synthesis. In wild AM rice, secondary metabolic and biotic stress-related analyses indicated that the jasmonic acid synthesis-related α-linolenic acid pathway, the phenolic and terpenoid pathways, as well as the phenolic and terpenoid syntheses-related mevalonate (MVA) pathway were more affected by the pathogen. Genes related to these pathways were more significantly enriched in wild AM rice than in cultivated AM rice in response to M. oryzae. On the other hand, genes associated with the ‘brassinosteroid biosynthesis’ were more enriched in cultivated AM rice.ConclusionsThe AMF R. intraradices-colonized rice plants exhibited greater resistance to M. oryzae than non-AMF-colonized plants. The findings of the current study demonstrate the potential effects of crop domestication on the benefits received by the host via root colonization with AMF(s), and provide new information on the underlying molecular mechanisms. In addition, results of this study can also help develop guidelines for the applications of AMF(s) when planting rice.