Saline-Alkali Tolerance in Rice: Physiological Response,Molecular Mechanism,and QTL Identification and Application to Breeding

Salinity-alkalinity is incipient abiotic stress that impairs plant growth and development. Rice (Oryza sativa) is a major food crop greatly affected by soil salinity and alkalinity, requiring tolerant varieties in the saline-alkali prone areas. Understanding the molecular and physiological mechanisms of saline-alkali tolerance paves the base for improving saline-alkali tolerance in rice and leads to progress in breeding. This review illustrated the physiological consequences, and molecular mechanisms especially signaling and function of regulating genes for saline-alkali tolerance in rice plants. We also discussed QTLs regarding saline-alkali tolerance accordingly and ways of deployment for improvement. More efforts are needed to identify and utilize the identified QTLs for saline-alkali tolerance in rice.     

东乡野生稻重要耐逆性状及其分子机制研究进展

东乡野生稻是全球分布最北的普通野生稻,具有丰富的抗逆性状,其育种利用价值高。本文综述了近年来东乡野生稻在耐冷、耐旱及抗虫等重要耐逆性状及其分子机制研究方面取得的进展,以期为水稻耐逆性的进一步研究提供依据。     

Drought Tolerance in Rice: Focus on Recent Mechanisms and Approaches

Drought stress is a serious limiting factor to rice production,which results in huge economic losses.It is becoming a more serious issue with respect to the global climate change.Keeping in view of the current and forecasted global food demand,it has become essential to enhance the crop productivity on the drought-prone rainfed lands with priority.In order to achieve the production target from rainfed areas,there is a requirement of rice varieties with drought tolerance,and genetic improvement for drought tolerant should be a high priority theme of research in the future.Breeding for drought tolerant rice varieties is a thought-provoking task because of the complex nature and multigenic control of drought tolerant traits would be a major bottleneck for the current research.A great progress has been made during last two decades in our understanding of the mechanisms involved in adaptation and tolerance to drought stress in rice.In this review,we highlighted the recent progresses in physiological,biochemical and molecular adaptation of rice to drought tolerance.A brief discussion on the molecular genetics and breeding approaches for drought tolerance in rice will be focused for the future crop improvement program for development of drought tolerant rice varieties.     

Hidden diversity for abiotic and biotic stress tolerances in the primary gene pool of rice revealed by a large backcross breeding program

Low and unstable rice productivity in many areas of Asia is associated with many abiotic and biotic stresses such as drought, salinity, anaerobic conditions during germination, submergence, phosphorus and zinc deficiency, etc. To develop rice varieties with tolerance to these stresses, we undertook a large backcross (BC) breeding effort for the last 6 years, using three recurrent elite rice lines and 203 diverse donors, which represent a significant portion of the genetic diversity in the primary gene pool of rice. Significant progress has been made in the BC breeding program, which resulted in development of large numbers of introgression lines with improved tolerance to these stresses. Promising lines have been developed with excellent tolerances (extreme phenotypes) to salinity, submergence and zinc deficiency; resistance to brown plant hopper, ability to germinate under the anaerobic condition and low temperature. Our results indicated that there exist tremendous amounts of ‘hidden’ diversity for abiotic and biotic stress tolerances in the primary gene pool of rice. Furthermore, we demonstrated that despite the complex genetics and diverse physiological mechanisms underlying the abiotic stress tolerances, introgression of genes from a diverse source of donors into elite genetic backgrounds through BC breeding and efficient selection (careful screening under severe stress) is a powerful way to exploit this hidden diversity for improving abiotic stress tolerances of rice. We have developed three large sets of introgression lines, which not only provide an unique platform of breeding materials for developing new rice cultivars with superior yield and stability by trait/gene pyramiding, but also represent unique genetic stocks for a large-scale discovery of genes/alleles underlying the abiotic and biotic stress tolerances of rice using genomic tools.     

Flooding Tolerance in Rice: Focus on Mechanisms and Approaches

Flooding is one of the most hazardous natural disasters and a major stress constraint to rice production throughout the world,which results in huge economic loss.Approximately one-fourth of the global rice crops(approximately 40 million hectares)are grown in rainfed lowland plots that are prone to seasonal flooding.A great progress has been made during last two decades in our understanding of the mechanisms involved in adaptation and tolerance to flooding/submergence in rice.In this review,we summarized the physiological and molecular mechanisms that contribute to tolerance of flooding/submergence in rice.We also covered various features of flooding stress with special reference to rice plants,viz.different types of flooding stress,environmental characterisation of flood water,impact of flooding stress on rice plant and their morphological,physiological and metabolic responses under flooding.A brief discussion on the tolerance mechanism in rice exhibited to different types of flooding will be focused for the future crop improvement programme for development of flooding tolerant rice variety.     

水稻耐冷性遗传及基因定位研究概况与展望

综述了水稻低温发芽力,幼苗期、孕穗期和开花期耐冷性等遗传研究概况和近年来在水稻耐冷性数量性状基因定位(QTLs)研究方面所取得的进展,并展望了今后的水稻耐冷性研究方向。     

水稻冷害研究现状及育种策略分析

介绍了冷害对水稻生产的影响,并对低温冷害类型、耐冷鉴定评价方法和耐冷生理研究进行初步分析,着重阐明水稻耐冷性育种的策略,通过挖掘耐冷资源来提高水稻耐冷性。首先,采用对现有品种、品系进行系统的耐冷性评价,作为配制杂交组合依据;其次,积极引进其它地区优良耐冷资源,加以改造利用;第三,利用籼粳稻亚远缘杂交或地理远缘杂交,再通过复交或回交优化性状组配,聚合有利基因,创造新材料来提高品种的耐冷性。     

Identification of Rice Accessions Associated with K~+/Na~+ Ratio and Salt Tolerance Based on Physiological and Molecular Responses

The key for rice plant survival under Na Cl salt stress is maintaining a high K~+/Na~+ ratio in its cells. Selection for salt tolerance rice genotypes based on phenotypic performance alone will delay in progress in breeding. Use of molecular markers in tandem with physiological studies will help in better identification of salt tolerant rice accessions. Eight rice accessions along with the check Dongjin were screened using 1/2 Yoshida solution with 50 mmol/L NaCl at the seedling stage. The accessions IT001158, IT246674, IT260533 and IT291341 were classified as salt tolerant based on their K~+/Na~+ ratios. Seventeen SSR markers reported to be associated with K~+/Na~+ ratio were used to screen the accessions. Five SSR markers(RM8053, RM345, RM318, RM253 and RM7075) could differentiate accessions classified based on their K~+/Na~+ ratios. Banding pattern of the accessions was scored compared to the banding pattern of Dongjin. The study differentiated accessions based on their association of K~+/Na~+ ratio with molecular markers which are very reliable. These markers can play a significant role in screening large set of rice germplasms for salt tolerance and also help in identification of high-yielding varieties with better salt tolerance. The salt tolerant accessions can be taken forward into developing better varieties by conventional breeding and exploring genes for salt tolerance.     

基于生物信息学的水稻候选SNP发掘

综述了现今广泛用于人类基因组计划的单核苷酸多态性（single nucleotide polymorphism,SNP）发掘的生物信息学方法及相关研究进展。介绍了目前已经开展的围绕水稻品质、抗（耐）性等性状的SNP发掘工作。结合自身的研究（包括HD-Zip转录因子编码基因等）,探讨了生物信息学方法用于水稻SNP发掘的可行性。最后阐述了SNP的开发对于水稻育种和功能基因组学研究的重要作用。     

水稻耐盐分子机制与育种研究进展

盐碱土壤对水稻不同生长发育时期均形成盐胁迫,进而导致水稻产量降低。耐盐水稻选育是提高水稻产量的有效途径。本文分析了盐胁迫对水稻不同发育时期农艺性状的影响,并从渗透调节、离子应答、激素调控和活性氧清除四个方面综述了近年来水稻耐盐分子机制的研究进展。最后,本文总结了水稻耐盐育种现状,并对耐盐水稻新品种的选育和推广进行了展望。     

Rayada specialty: the forgotten resource of elite features of rice

Crop domestication and thereafter gradual selection or directional breeding have narrowed the genetic diversity of elite varieties and even promoted gathering of deleterious mutations in their stress response mechanisms, whereas local ecotypes, landraces and wild relatives still growing on native environment and preferences keep the genetic diversities for features like stress tolerance. Rayada is such an exceptional ecotype, variant of typical deepwater rice, completely endemic to certain areas of Madhumati river tracts of Bangladesh and still shares some features of wild rices. Multiple physiological features of Rayadas are distinctly different from typical deepwater rice. Tolerance to prolonged flood, submergence and cold are special features along with strong photoperiod sensitivity and lack of dormancy. Moreover, longer root system and prompt recovery capacity make it as an elite resource of stress tolerance. However, it has long been neglected because of mainly its long life cycle and poor yield. This review examines the specialty of Rayada rice and the potential use of its unique traits.     

Germplasm Enhancement and Breeding Strategies for Crop Quality in Japan

Abstract

Rice is the staple food for most Asians. Breeding efforts at the national and international levels have resulted in high-yielding varieties with resistance/tolerance to biotic and abiotic constraints. Consequently Asia has enjoyed rice self-sufficiency in recent years. Now in some countries over-production of rice has occurred, partly because of reduced rice consumption. For instance, in 1962 Japan had a per capita rice consumption of 118.3 kg and then this rapidly declined to about 60kg in 2003. Imbalances between production and consumption in rice and other crops have promoted a paradigm shift of breeding objectives oriented from producers to consumers. Germplasm enhancement (pre-breeding) and breeding strategies now focus on a broad range of crop and food qualities, which are closely associated with industrial and processing properties and human health and nutrition. In particular, physiological functions of chemical compounds involved in crop products are being studied as a part of breeding programs. Diverse plant genetic resources and advances in plant genome research have contributed to successful breeding strategies to improve and manage crop and food quality. Recent progress in germplasm enhancement and breeding strategies for quality improvement of rice, wheat, soybean and sweet potato in Japan is discussed.     

几种杂交水稻及其亲本三系幼苗抗冷特性的比较

根据杂交水稻抗冷性选育种的需要,我们研究了低温对五个杂交水稻组合的影响从低温对幼苗根系电解质泄漏,黄化幼苗转绿和幼苗存活率的影响来看:根系外渗液的相对电导率增加,叶绿素合成能力的降低与幼苗存活率具有一致性,其抗冷顺序为粳稻型的秀优57>籼稻型的青优早>汕优63、汕优64和成优64。杂交水稻F_1的抗冷性与母本近似,与父本关系不大,保持系的抗冷性相似于不育系。本文对该结果在杂交水稻抗冷性选育中的意义进行了讨论。     

东乡野生稻研究进展及育种利用策略

东乡野生稻是目前世界上已发现的分布最北（N 28°14′、E 116°36′）的野生稻特异种质资源,其基因组中蕴含着抗病、抗虫、耐逆及其他诸多优良基因/QTL,前人已对其开展了大量的研究。本文从抗病、抗虫、抗逆、育性、产量及其他优良特性等方面总结了东乡野生稻的研究进展,并提出了其育种利用策略。     

几种杂交水稻及其亲本三系幼苗抗冷特性的比较

 根据杂交水稻抗冷性选育种的需要，我们研究了低温对五个杂交水稻组合的影响。从低温对幼苗根系电解质泄漏，黄化幼苗转绿和幼苗存活率的影响来看：根系外渗液的相对电导率增加，叶绿素合成能力的降低与幼苗存活率具有一致性，其抗冷顺序为粳稻型的秀优57>籼稻型的青优早>汕优63、汕优64和威优64。杂交水稻Fl的抗冷性与母本近似．与父本关系不大。保持系的抗冷性相似于不育系。本文对该结果在杂交水稻抗冷性选育中的意义进行了讨论。     

水稻耐盐基因定位与克隆及品种耐盐性分子标记辅助选择改良研究进展

土壤盐渍化严重制约水稻生产发展,提高耐盐性已成为水稻育种的重要目标之一。挖掘水稻耐盐新基因,解析其分子作用机制可以为水稻耐盐性遗传改良奠定基础。本文从定位群体、耐盐性鉴定时期和鉴定方法、耐盐性评价指标、鉴定到的耐盐QTL、耐盐QTL的精细定位和图位克隆等方面,总结了近年来水稻耐盐QTL定位研究中所取得的进展;介绍了水稻耐盐/盐敏感突变体筛选和基因克隆以及耐盐性关联分析的研究近况;并对水稻耐盐性分子标记辅助选择改良的现状作了概述。     

Toward Understanding Molecular Mechanisms of Abiotic Stress Responses in Rice

Plants have evolved delicate mechanisms to cope with environmental stress. Following exposure to environmental stimuli, extracellular signals are perceived and transmitted through signal transduction cascades. Upon receipt and transmission of the signals, a number of stress-related genes are induced, leading to stress adaptation in plant cells. Rice, which is a critical food grain for a large portion of the world’s population, is frequently impacted by several abiotic stressors, the most important of which are drought, salinity, and cold. Exposure to environmental conditions outside of acceptable tolerance ranges can negatively affect rice growth and production. In this paper, a review of rice responses to abiotic stress is presented, with particular attention to the genes and pathways related to environmental stress tolerance. It is apparent that, while progress has been made in identifying genes involved in stress adaptation, many questions remain. Understanding the mechanisms of stress response in rice is important for all research designed to develop new rice varieties with improved tolerance.     

辽宁省杂草稻幼苗对低温胁迫的生理响应

 以杂草稻WR03 45和WR03 26为研究材料,以栽培稻丽江新团黑谷为对照,采用人工气候箱培养,研究了低温胁迫（5 ℃）对杂草稻幼苗期叶片和根系生理指标的影响。结果表明,除叶绿素和类胡萝卜素含量外,杂草稻叶片各生理指标的变化规律与对照相似; 杂草稻根系硫代巴比妥酸反应产物（TBARS）和脯氨酸的变化规律与对照不同,外渗电导率和可溶性糖含量的变化规律与对照相似。低温对WR03 45和丽江新团黑谷的光合系统损伤较小;低温胁迫后,WR03 45细胞膜系统保持完整,膜脂过氧化程度小于其他材料;WR03 45可溶性糖含量和脯氨酸含量均高于对照品种。5 ℃低温对杂草稻WR03 45伤害较小,表明WR03 45具有较强的苗期耐冷性。     

Genetic Improvement of Rice for Bacterial Blight Resistance: Present Status and Future Prospects

The production and productivity of rice has been challenged due to biotic and abiotic factors. Bacterial blight (BB) disease, caused by Xanthomonas oryzae pv. oryzae, is one of the important biotic stress factors, which reduces rice production by 20%–50%. The deployment of host plant resistance is the most preferred strategy for management of BB disease, and breeding disease resistant varieties remains a very economical and effective option. However, it is difficult to develop rice varieties with durable broad-spectrum resistance against BB using conventional approaches alone. Modern biotechnological tools, particularly the deployment of molecular markers, have facilitated the cloning, characterization and introgression of BB resistance genes into elite varieties. At least 46 BB resistance genes have been identified and mapped from diverse sources till date. Among these, 11 genes have been cloned and characterized. Marker-assisted breeding remains the most efficient approach to improve BB resistance by introducing two or more resistance genes into target varieties. Among the identified genes, xa5, xa13 and Xa21 are being widely used in marker-assisted breeding and more than 70 rice varieties or hybrid rice parental lines have been improved for their BB resistance alone or in combination with genes/QTLs conferring tolerance to other stress. We review the developments related to identification and utilization of various resistance genes to develop BB resistant rice varieties through marker-assisted breeding.     

一个水稻铜锌SOD酶基因在应答亚砷酸盐胁迫中的作用

【目的】水稻Os08g44770.1基因编码一个铜锌SOD酶,但其在响应亚砷酸盐[As(Ⅲ)]胁迫中的生物学功能未知。本研究旨在深入揭示由该基因调控水稻砷耐性改变的分子机理并为水稻抗逆育种提供理论参考。【方法】以野生型日本晴(WT)和2个Os08g44770.1过表达转基因株系为试材,通过胁迫处理、生理指标测定和基因表达分析等,系统探究了转基因植株对As(Ⅲ)的耐受性表现,并初步揭示了其调控水稻砷耐性的生理和分子机理。【结果】与WT相比,过表达转基因株系对As(Ⅲ)更加敏感;转基因植株在砷胁迫下的根系相对伸长量、生物量(干质量)、叶绿素含量、根系细胞质膜完整性、叶片抗氧化程度等均显著低于WT;Os08g44770.1在砷处理后的WT和转基因植株叶片中的表达模式略有不同,但均表现为处理24 h时被显著诱导表达。【结论】过度表达Os08g44770.1基因可导致水稻的砷耐受性极显著下降。