Transferring Translucent Endosperm Mutant Gene Wx-mq and Rice Stripe Disease Resistance Gene Stv-bi by Marker-Assisted Selection in Rice (Oryza sativa)

A high-yielding japonica rice variety, Wuyunjing 7, bred in Jiangsu Province, China as a female parent was crossed with a Japanese rice variety Kantou 194, which carries a rice stripe disease resistance gene Stv-b＇ and a translucent endosperm mutant gene Wx-mq. From F2 generations, a sequence characterized amplified region （SCAR） marker tightly linked with Stv-b＇ and a cleaved amplified polymorphic sequence （CAPS） marker for Wx-mq were used for marker-assisted selection. Finally, a new japonica rice line, Ning 9108, with excellent agronomic traits was obtained by multi-generational selection on stripe disease resistance and endosperm appearance. The utilization of the markers from genes related to rice quality and disease resistance was helpful not only for establishing a marker-assisted selection system of high-quality and disease resistance for rice but also for providing important intermediate materials and rapid selection method for good quality, disease resistance and high yield in rice breeding.

Study on a Mutant with Low Content Chlorophyll b in a High Yielding Rice and Its Photosynthesis Properties

A high yielding rice mutant ( Oryza sativa L. cv. Zhenhui 249) with low chlorophyll b was recently discovered in the field. The mutant was mainly characterized by the decrease of the content of extrinsic antennae complex. This variation was shown in the stage when the leaves were expanding. When the leaves are at the final developmental stage, the content would approach to that of the wild type. It was discovered that only moderate amount of chlorophyll b decreased in this mutant. The photosynthetic apparatus of the mutant was rather stable in the whole life span of the leaf. The extrinsic antennae complex of the mutant might make efficient use of light and meanwhile reduce the production of O -· 2.

Physiological Character and Gene Mapping in a New Green-revertible Albino Mutant in Rice

A green-revertible albino mutant-Qiufeng M was found from the japonica rice （Oryza sativa L. ssp. japonica） Qiufeng in the field. The first three leaves of the mutant were albino with some green. The leaf color became pale green since the fourth leaf and the glume had the same phenomenon as the first three leaves. The measuring data of the pigment content confirmed the visually observed results. It truly had a remarkable changing process in the leaf color in Qiufeng M. Comparison of the main agronomic characters between Qiufeng and Qiufeng M indicated that the neck length and grain weight showed significant difference at the 1% level, and other characters were not different. Genetic analysis showed that the green-revertible albino trait was controlled by a single recessive nucleic gene. Using 209 recessive mutant individuals in the F2 population derived from the cross Pei＇ai 64S × Qiufeng M, a gene, tentatively named gra（t）, was located between the SSR markers of RM475 and RM2-22 on the long arm of chromosome 2. The genetic distance were 17.3 cM and 2.9 cM respectively.

Morphological,Anatomical and Genetic Analysis for a Rice Mutant with Abnormal Hull

A mutant with abnormal hull was first discovered from a twin-seedling strain W2555 in rice （Oryza sativa L.）. The mutant had sparse branches and decreased number of florets from the base to the peak. Frequently, the florets at the top of the panicle did not develop completely. The underdeveloped florets often showed slender and white in their life cycle. Genetic analysis indicated that the mutant traits were controlled by a single recessive gene （temporarily designated as ah）. ah gene controlled the development of inflorescence meristem and the flower organ. The florets of mutant showed degenerated lemma and palea. Stamens and lodicules were homeoticly transformed into pistils and palea/lemma-like structures, respectively. It seemed that ah mutant phenotypes of the homeotic conversions in lodicules and stamens were very similar to that of the B loss-of-function spwl gene reported previously in rice.

Grain Filling Characteristics of Giant Embryo Rice Mutant

[Objective] The aim was to explore the relevance between decreased 1 000-grain weight and grain-filling characteristics of rice giant embryo mutant.[Method] Richards equation was used to describe grain filling processes of giant embryo mutant MH-ge1 and its corresponding wild type so as to analyze the parameters of grain-filling characteristics of materials.[Result] The initial filling power of mutant MH-ge1 was higher than the wild type MH86,however,the maximum filling rate,the mean filling rate and the final increment of mutant MH-ge1 was lower than those of MH86.[Conclusion] The grain-filling characteristics of mutant MH-ge1 were poorer than the wild type MH86,thus resulting in the decrease of the grain weight of the giant embryo rice.

Morphological and Anatomical Analyses of a Floral Organ Mutant in Rice

A spontaneously occurred rice ( Oryza sativa L.) mutant characterized by homeotic conversions in glumes and stamens was found in the progeny of a breeding material. The mutant plant shows degenerated glumes and morphological transformation of stamens into pistils. A mutant floret consists of 1 to 3 completely developed pistils and 4 to 6 incomplete pistils with no ovary. Some pistilloid stamens still have filaments but tipped by bulged tissue and 0 to 3 stigmas. Three ovaries in a single floret were observed in its cross and longitudinal sections. When the mutant plants were pollinated with pollens from wild type plants, one or two naked seeds instead of a caryopsis could be produced in a single floret. The mutant is controlled by a single recessive gene since its F 1 hybrid plants were restored to wild type and 3∶1 ratio of wild type to mutant plants were observed in the progeny of heterozygotes. It seems that the mutant phenotype of the homeotic conversions in glumes and stamens is similar to that of the B loss_of_function mutants in Arabidopsis and Antirrhinum .

Quality Research on the Purple Leaf Mutant of Rice——PLM

[Objective] The aim was to carry out the quality research on a purple leaf mutant （PLM） of rice and provide the basis for applied research of purple rice.[Method] A newly discovered purple mutant of rice and its hybrid filial generations （F1 and F2） were employed as the experimental materials to determine its characteristic indexes,such as grain type,chalky grain rate,chalkiness,1 000-grain weight,brown rice percentage,protein content,amylose content,gelatinization temperature and consistency.[Result] The grain type and brown rice percentage of the parent （pro-Z） both reached standard of Ⅰ Grade,while chalky grain rate,chalkiness,amylose content and consistency did not meet the requirements of the standard.The F2 generation displayed some optimized properties,including larger grain,lower amylose content,reduced chalkiness,lower chalky grain rate and softened consistency.[Conclusion] The majority of the characteristic indexes of pro-Z did not meet the requirements of standard,but the qualities of F2 generation were all optimized to some extent.

Morphological Analysis and Gene Mapping of a Rice Dwarf Mutant

[Objective] This study aimed to conduct morphological analysis and gene mapping of a rice dwarf mutant. [Method] A dwarf mutant （Xiaoxiang＇ai） was used as test material for morphological observation. Xiaoxiang＇ai was used as female parent and semi-dwarf material Xiangzao143 was used as male parent to construct populations for genetic analysis. Gene mapping was conducted by using micro- satellite markers. [Result] The average height of Xiaoxiang＇ai was 55 cm; genetic analysis results showed that plant height of F1 individuals was similar with the male parent, while semi-dwarf plants and dwarf plants were observed in F2 populations and the segregation ratio was nearly 3：1, indicating that plant height trait of Xiaoxi- ang＇ai is mainly controlled by one pair of recessive gene located on rice chromo- some 5 and in the upstream of RM249, with a genetic distance of 8.4 cM. [Conclu- sion] rRH is a new dwarf gene in rice.

Fine mapping and marker-assisted selection (MAS) of a low glutelin content gene in rice

Rice with low glutelin content is suitable as functional food for patients affected with diabetes and kidney failure. The fine mapping of the gene(s) responsible for low glutelin content will provide information regarding the distribution of glutelin related genes in rice genome and will generate markers for the selection of low glutelin rice varieties. Following an SDS-PAGE screen of rice germplasm from Taihu Valley of China, Japonica selection W3660 is identified to be a novel mutant characterized with low glutelin content. For fine mapping the mutant gene for low glutelin content, F2 and F3 populations were derived from a cross between W3660 and Jingrennuo. SDS-PAGE analysis of the total endosperm protein showed that the low glutelin content trait was controlled by a single dominant nuclear gene. Genetic mapping, using SSRs, located this gene to chromosome 2, in the region between SSR2-001/SSR2-004 and RM1358. The dis- tances of the two markers to the target gene were 1.1 cM and 3.8 cM respectively. By semi-quantitative RT-PCR analysis, the transcripts of GluB4/GluB5 genes located within the region do not change. However, GluB5 gene located proximal to SSR2-001/SSR2-004 was specifically reduced. SSR profiles of seven Japonica varieties were compared with that of W3660 for loci in the relevant genetic region. The markers SSR2-004 and RM1358 were used for marker- assisted selection. The selection efficiencies of SSR2-004 and RM1358 were 96.8% and 92.7% respectively. This provides a standard starting point for the breeding of low glutelin content rice varieties in China.

Genetic analysis and fine-mapping of a dwarfing with withered leaf-tip mutant in rice

A dwarf mutant of rice （Oryza sativa L.） by mutagenesis of ethylene methylsulfonate （EMS） treatment from Nipponbare was identified. The mutant exhibited phenotypes of dwarfism and withered leaf tip （dwll）. Based on the intemode length of dwll, this mutant belongs to the dm type of dwarfing. Analysis of elongation of the second sheath and m-amylase activity in endosperm showed that the phenotype caused by dwll was insensitive to gibberellin acid treatment. Using a large F2 population derived from a cross between the dwll and an indica rice variety, TN1, the DWL1 gene was mapped to the terminal region of the long arm of chromosome 3. Fine-mapping delimited it into a 46 kb physical distance between two STS markers, HL921 and HL944, where 6 open reading frames were predicted. Cloning of DWL1 will contribute to dissecting molecular mechanism that regulates plant height in rice, which will be beneficial to molecular assisted selection of this important trait.

Genetic Analysis and Molecular Mapping of a Novel Chlorophyll-Deficit Mutant Gene in Rice

A rice etiolation mutant 824ys featured with chlorophyll deficiency was identified from a normal green rice variety 824B. It showed whole green-yellow plant from the seedling stage, reduced number of tillers and longer growth duration. The contents of chlorophyll, chlorophyll a, chlorophyll b and net photosynthetic rate in leaves of the mutant obviously decreased, as well as the number of spikelets per panicle, seed setting rate and 1000-grain weight compared with its wild-type parent. Genetic analyses on F1 and F2 generations of 824ys crossed with three normal green varieties showed that the chlorophyll-deficit mutant character was controlled by a pair of recessive nuclear gene. Genetic mapping of the mutant gene was conducted by using microsatellite markers and F2 mapping population of 495R/824ys, and the mutant gene of 824ys was mapped on the short arm of rice chromosome 3. The genetic distances from the target gene to the markers RM218, RM282 and RM6959 were 25.6 cM, 5.2 cM and 21.8 cM, respectively. It was considered to be a new chlorophyll-deficit mutant gene and tentatively named as chill（t）.

Screening for Spikelet Fertility and Validation of Heat Tolerance in a Large Rice Mutant Population

A total of 10 000 M4 individuals in Jao Hom Nil (JHN) mutant population was treated with high temperature (40 ℃ to 45 ℃) during the day time (6 h) from the booting to the harvesting stages, and ambient temperature (33 ℃ to 35℃) was used as the control. The results of screening and yield trials found that the mutant line M9962 had a high spikelet fertility of 78% under heat stress. In addition, the other mutant lines, including M3181 and M7988, had a spikelet fertility of approximately 70%. However, the JHN wild type, Sin Lek, RD15 and RD33 had very low spikelet fertility of 34%, 14%, 9% and 4%, respectively. The lower spikelet fertility at an elevated temperature resulted in a dramatic decrease of filled grain and contributed to a loss in 100-grain weight. M9962 is a potential genetic stock for use in a heat tolerance breeding programme. In addition, spikelet fertility at high temperature was representative of heat tolerance and can be used as a screening trait for heat tolerance during the reproductive phase on a large scale.

Characterization and mapping of a novel light-dependent lesion mimic mutant lmm6 in rice(Oryza sativa L.)

A novel rice lesion mimic mutant (LMM) was isolated from an ethane methyl sulfonate (EMS)-induced 02428 mutant bank. The mutant, tentatively designated as lmm6, develops necrotic lesions in the whole growth period along with changes in several important agronomic traits. We found that the initiation of the lesions was induced by light and cel death occurred in lmm6 accompanied with accumulation of reactive oxygen species (ROS). The lower chlorophyl content, soluble protein content and superoxide dismutase (SOD) activity, the higher malondialdehyde (MDA) content were detected in lmm6 than in the wild type (WT). Moreover, the observation by transmission electronic microscope (TEM) demonstrated that some organel es were damaged and the stroma lamel a of chloroplast was irregular and loose in mesophyl cel of lmm6. In addition, lmm6 was more resistant than WT to rice blast fungus Magnaporthe grisea infection, which was consistent with increased expression of four genes involved in the defense-related reaction. Genetic analysis showed that mutant trait of lmm6 is inherited as a monogenic recessive nuclear gene located on the long arm of chromosome 6. Using simple sequence repeat (SSR) markers, the target gene was ifnal y delimited to an interval of 80.8 kb between markers MM2359 and MM2370, containing 7 annotated genes. Taken together, our results provide the information to identify a new gene involved in rice lesion mimic, which wil be helpful in clarifying the mechanism of cel death and disease resistance in rice.

Genetic Analysis and Mapping of TWH Gene in Rice Twisted Hull Mutant

A mutant with twisted hulls was found in a breeding population of rice （Oryza sativa L.）. The mutant shows less grain weight and inferior grain quality in addition to twisted hulls. Genetic analysis indicated that the phenotype of mutant was controlled by a single recessive gene （temporarily designated as TW（H）. To map the TWH gene, an F2 population was generated by crossing the twh mutant to R725, an indica rice variety with normal hulls. For bulked segregant analysis, the bulk of mutant plants was prepared by mixing equal amount of plant tissue from 10 twisted-hull plants and the bulk of normal plants was obtained by pooling equal amount tissue of 10 normal-hull plants. Two hundred and seven pairs of simple sequence repeat （SSR） primers, which are distributed on 12 rice chromosomes, were used for polymorphism analysis of the parents and the two bulks. The TWH locus was initially mapped close to the SSR marker RM526 on chromosome 2. Therefore, further mapping was performed using 50 pairs of SSR primers around the marker RM526. The TWH was delimited between the SSR markers RM14128 and RM208 on the long arm of chromosome 2 at the genetic distances of 1.4 cM and 2.7 cM, respectively. These results provide the foundation for further fine mapping, cloning and functional analysis of the TWH gene.

Improving the phenotypic expression of rice genotypes:Rethinking “intensification” for production systems and selection practices for rice breeding

Intensification in rice crop production is generally understood as requiring increased use of material inputs: water, inorganic fertilizers, and agrochemicals. However, this is not the only kind of intensification available. More productive crop phenotypes, with traits such as more resistance to biotic and abiotic stresses and shorter crop cycles, are possible through modifications in the management of rice plants, soil, water, and nutrients, reducing rather than increasing material inputs. Greater factor productivity can be achieved through the application of new knowledge and more skill, and(initially) more labor, as seen from the System of Rice Intensification(SRI), whose practices are used in various combinations by as many as 10 million farmers on about 4 million hectares in over 50 countries. The highest yields achieved with these management methods have come from hybrids and improved rice varieties, confirming the importance of making genetic improvements. However,unimproved varieties are also responsive to these changes, which induce better growth and functioning of rice root systems and more abundance, diversity, and activity of beneficial soil organisms. Some of these organisms as symbiotic endophytes can affect and enhance the expression of rice plants' genetic potential as well as their phenotypic resilience to multiple stresses, including those of climate change. SRI experience and data suggest that decades of plant breeding have been selecting for the best crop genetic endowments under suboptimal growing conditions, with crowding of plants that impedes their photosynthesis and growth, flooding of rice paddies that causes roots to degenerate and forgoes benefits derived from aerobic soil organisms, and overuse of agrochemicals that adversely affect these organisms as well as soil and human health. This review paper reports evidence from research in India and Indonesia that changes in crop and water management can improve the expression of rice plants' genetic potential, thereby creating more productive and robustphenotypes from given rice genotypes. Data indicate that increased plant density does not necessarily enhance crop yield potential, as classical breeding methods suggest. Developing cultivars that can achieve their higher productivity under a wide range of plant densities—breeding for density-neutral cultivars using alternative selection strategies—will enable more effective exploitation of available crop growth resources. Density-neutral cultivars that achieve high productivity under ample environmental growth resources can also achieve optimal productivity under limited resources, where lower densities can avert crop failure due to overcrowding. This will become more important to the extent that climatic and other factors become more adverse to crop production. Focusing more on which management practices can evoke the most productive and robust phenotypes from given genotypes is important for rice breeding and improvement programs since it is phenotypes that feed our human populations.

Use of Selection Indices Based on Multivariate Analysis for Improving Grain Yield in Rice

In order to study selection indices for improving rice grain yield, a cross was made between an Iranian traditional rice (Oryza sativa L.) variety, Tarommahalli and an improved indica rice variety, Khazar in 2006. The traits of the parents (30 plants), F1 (30 plants) and F2 generations (492 individuals) were evaluated at the Rice Research Institute of Iran (RRII) during 2007. Heritabilities of the number of panicles per plant, plant height, days to heading and panicle exsertion were greater than that of grain yield. The selection indices were developed using the results of multivariate analysis. To evaluate selection strategies to maximize grain yield, 14 selection indices were calculated based on two methods (optimum and base) and combinations of 12 traits with various economic weights. Results of selection indices showed that selection for grain weight, number of panicles per plant and panicle length by using their phenotypic and/or genotypic direct effects (path coefficient) as economic weights should serve as an effective selection criterion for using either the optimum or base index.

Genomic selection: A breakthrough technology in rice breeding

Rice(Oryza sativa)provides a staple food source for more than half the world population.However,the current pace of rice breeding in yield growth is insufficient to meet the food demand of the everincreasing global population.Genomic selection(GS)holds a great potential to accelerate breeding progress and is cost-effective via early selection before phenotypes are measured.Previous simulation and experimental studies have demonstrated the usefulness of GS in rice breeding.However,several affecting factors and limitations require careful consideration when performing GS.In this review,we summarize the major genetics and statistical factors affecting predictive performance as well as current progress in the application of GS to rice breeding.We also highlight effective strategies to increase the predictive ability of various models,including GS models incorporating functional markers,genotype by environment interactions,multiple traits,selection index,and multiple omic data.Finally,we envision that integrating GS with other advanced breeding technologies such as unmanned aerial vehicles and open-source breeding platforms will further improve the efficiency and reduce the cost of breeding.

Status and Perspectives on the Researches of Rice Glutelin Mutants

Rice (Oryza sativa L. ) is one of the model plants for genomics research. As the raising of functional rice breeding for special usage, glutelin mutants play a more and more important role in the functional rice breeding as well as eukaryotic gene expression and regulation research materials. For example, the rice cultivar special for the patients suffering from kidney disease and diabetes could be developed from the rice glutelin mutants. In this paper, current researches on characterization, mutation mechanism and breeding usage of various rice glutelin mutants, especially the low glutelin content cultivars, were all discussed with perspectives on the trends of the glutelin mutant researches in the era of post-genomics.

Genetic Analysis and Gene Mapping of a Rice Tiller Angle Mutant tac2

Tiller angle, a very essential agronomic trait, is significant in rice breeding, especially in plant type breeding. A tiller anglo controlling 2 （tac2） mutant was obtained from a restorer line Jinhui 10 by ethyl methane sulphonate mutagenesis. The tac2 mutant displayed normal phenotype at the seedling stage and the tiller angle significantly increased at the tillering stage, A preliminary physiological research indicated that the mutant was sensitive to GA. Thus, it is speculated that TAC2 and TAC1 might control the tiller angle in the same way. Genetic analysis showed that the mutant trait was controlled by a major recessive gene and was located on chromosome 9 using SSR markers. The genetic distances between TAC2 and its nearest markers RM3320 and RM201 were 19.2 cM and 16,7 cM, respectively.

Deciphering Rice Lesion Mimic Mutants to Understand Molecular Network Governing Plant Immunity and Growth

Plant lesion mimic mutants(lmms)generally possess autoimmunity and hypersensitive response(HR)-like cell death in the absence of biotic or abiotic stress.They have attracted much attention because they are useful tools for deciphering the interaction between defense signaling and growth.Recent studies have identified more than 30 lmms involved in the plant immune response and cell death in rice.Genes underlying these lmms,coding for diverse types of proteins,mainly regulate transcription,protein translation and modification,vesicular trafficking and catalyzation of metabolism.Here,we presented an overview of the most recent advances on the study of lmms in rice and proposed a perspective on potential utilization of LMM genes in agriculture.