Transgenic approaches for genetic improvement in groundnut (Arachis hypogaea L.) against major biotic and abiotic stress factors

Cultivated groundnut (Arachis hypogaea L.) is considered as one of the primary oilseed crops and a major fodder for cattle industry in most of the developing countries, owing to its rich source of protein. It is due to its geocarpic nature of growth that the overall yield performance of groundnut is hindered by several biotic and abiotic stress factors. Multidimensional attempts were undertaken to combat these factors by developing superior groundnut varieties, modified with integral mechanism of tolerance/resistance; however this approach proved to be futile, owing to inferior pod and kernel quality. As a superior alternative, biotechnological intervention like transformation of foreign genes, either directly (biolistic) or via Agrobacterium, significantly aided in the development of advanced groundnut genotypes equipped with integral resistance against stresses and enhanced yield attributing traits. Several genes triggered by biotic and abiotic stresses, were detected and some of them were cloned and transformed as major parts of transgenic programmes. Application of modern molecular biological techniques, in designing biotic and abiotic stress tolerant/resistant groundnut varieties that exhibited mechanisms of resistance, relied on the expression of specific genes associated to particular stress. The genetically transformed stress tolerant groundnut varieties possess the potential to be employed as donor parents in traditional breeding programmes for developing varieties that are resilient to fungal, bacterial, and viral diseases, as well as to draught and salinity. The present review emphasizes on the retrospect and prospect of genetic transformation tools, implemented for the enhancement of groundnut varieties against key biotic and abiotic stress factors.     

Phenotyping for Abiotic Stress Tolerance in Maize

The ability to quickly develop germplasm having tolerance to several complex polygenic inherited abiotic and biotic stresses combined is critical to the resilience of cropping systems in the face of climate change.Molecular breeding offers the tools to accelerate cereal breeding;however,suitable phenotyping proto-cols are essential to ensure that the much-anticipated benefits of molecular breeding can be realized.To facilitate the full potential of molecular tools,greater emphasis needs to be given to reducing the within-experimental site variability,application of stress and characterization of the environment and appropriate phenotyping tools.Yield is a function of many processes throughout the plantcycle,and thus integrative traits that encompass crop performance over time or organization level(i.e.canopy level) will provide a better alternative to instantaneous measurements which provide only a snapshot of a given plant process.Many new phenotyping tools based on remote sensing are now available including non-destructive measurements of growth-related parameters based on spectral reflectance and infrared thermometry to estimate plant water status.Here we describe key field phenotyping protocols for maize with emphasis on tolerance to drought and low nitrogen.     

Rhizosphere engineering and management for sustainable agriculture

This paper reviews strategies for manipulating plants and their root-associated microorganisms to improve plant health and productivity. Some strategies directly target plant processes that impact on growth, while others are based on our knowledge of interactions among the components of the rhizosphere (roots, microorganisms and soil). For instance, plants can be engineered to modify the rhizosphere pH or to release compounds that improve nutrient availability, protect against biotic and abiotic stresses, or encourage the proliferation of beneficial microorganisms. Rhizobacteria that promote plant growth have been engineered to interfere with the synthesis of stress-induced hormones such as ethylene, which retards root growth, and to produce antibiotics and lytic enzymes active against soilborne root pathogens. Rhizosphere engineering also can involve the selection by plants of beneficial microbial populations. For example, some crop species or cultivars select for and support populations of antibiotic-producing strains that play a major role in soils naturally suppressive to soil-borne fungal pathogens. The fitness of root-associated bacterial communities also can be enhanced by soil amendment, a process that has allowed the selection of bacterial consortia that can interfere with bacterial pathogens. Plants also can be engineered specifically to influence their associated bacteria, as exemplified by quorum quenching strategies that suppress the virulence of pathogens of the genus Pectobacterium. New molecular tools and powerful biotechnological advances will continue to provide a more complete knowledge of the complex chemical and biological interactions that occur in the rhizosphere, ensuring that strategies to engineer the rhizosphere are safe, beneficial to productivity, and substantially improve the sustainability of agricultural systems.     

Combinatorial Interactions of Biotic and Abiotic Stresses in Plants and Their Molecular Mechanisms: Systems Biology Approach

Plants are continually facing biotic and abiotic stresses, and hence, they need to respond and adapt to survive. Plant response during multiple and combined biotic and abiotic stresses is highly complex and varied than the individual stress. These stresses resulted alteration of plant behavior through regulating the levels of microRNA, heat shock proteins, epigenetic variations. These variations can cause many adverse effects on the growth and development of the plant. Further, in natural conditions, several abiotic stresses causing factors make the plant more susceptible to pathogens infections and vice-versa. A very intricate and multifaceted interactions of various biomolecules are involved in metabolic pathways that can direct towards a cross-tolerance and improvement of plant’s defence system. Systems biology approach plays a significant role in the investigation of these molecular interactions. The valuable information obtained by systems biology will help to develop stress-resistant plant varieties against multiple stresses. Thus, this review aims to decipher various multilevel interactions at the molecular level under combinatorial biotic and abiotic stresses and the role of systems biology to understand these molecular interactions.     

Genetic and genomic approaches to develop rice germplasm for problem soils

Soils that contain toxic amounts of minerals or are deficient in essential plant nutrients are widespread globally and seriously constrain rice production. New methods are necessary to incorporate the complex adaptive traits associated with tolerance of these abiotic stresses, while simultaneously retaining the high yield potential of rice varieties when conditions are favorable. Significant progress in the genetic characterization of stress response pathways and recent advances in genomics have provided powerful tools for in-depth dissection of tolerance mechanisms. Additionally, tolerance of most of these abiotic stresses in rice is controlled by a few QTLs with large effects despite the intricacy of the numerous traits involved. Genetic dissection of these QTLs and their incorporation into high-yielding varieties will significantly enhance and stabilize rice productivity in these problem soils. Current efforts at IRRI and in rice breeding programs worldwide are seeking to explore diverse germplasm collections and genetically dissect the causal mechanisms of tolerance to facilitate their use in breeding. This review focuses on salinity and P and Zn deficiency as the major problems encountered in rice soils, and examines current understanding of the mechanisms involved and efforts toward germplasm improvement.     

Molecular approaches for genetic improvement of seed quality and characterization of genetic diversity in soybean: a critical review

Soybean is an economically important leguminous crop. Genetic improvements of soybeans have focused on enhancement of seed and oil yield, development of varieties suited to different cropping systems, and breeding resistant/tolerant varieties for various biotic and abiotic stresses. Plant breeders have used conventional breeding techniques for the improvement of these traits in soybean. The conventional breeding process can be greatly accelerated through the application of molecular and genomic approaches. Molecular markers have proved to be a new tool in soybean breeding by enhancing selection efficiency in a rapid and time-bound manner. An overview of molecular approaches for the genetic improvement of soybean seed quality parameters, considering recent applications of marker-assisted selection and ‘omics’ research, is provided in this article.     

Biotechnological perspectives of microbes in agro-ecosystems

In subsistence agricultural systems, crop yields are directly dependent on the inherent soil fertility and on microbial processes that govern the mineralization and mobilization of nutrients required for plant growth. An impact of different crop species that are used in various combinations is likely to be an important factor in determining the structure of plant beneficial microbial communities that function in nutrient cycling, the production of plant growth hormones, and suppression of root diseases. In addition, studies are needed to elucidate the signal transduction pathways that result from treatment of plants with plant growth-promoting rhizobacteria under stress conditions. In the present review an emphasis has been given on plant–microbe interactions and their mitigation under abiotic and biotic stresses.     

Harnessing rhizobacteria to fulfil inter-linked nutrient dependency on soil and alleviate stresses in plants

Plant rhizo-microbiome comprises complex microbial communities that colonize at the interphase of plant roots and soil. Plant growth-promoting rhizobacteria (PGPR) in the rhizosphere provide important ecosystem services ranging from the release of essential nutrients for enhancing soil quality and improving plant health to imparting protection to plants against rising biotic and abiotic stresses. Hence, PGPR serve as restoring agents to rejuvenate soil health and mediate plant fitness in the facet of changing climate. Though it is evident that nutrient availability in soil is managed through inter-linked mechanisms, how PGPR expedite these processes remain less recognized. Promising results of PGPR inoculation on plant growth are continually reported in controlled environmental conditions, however, their field application often fails due to competition with native microbiota and low colonization efficiency in roots. The development of highly efficient and smart bacterial synthetic communities by integrating bacterial ecological and genetic features provides better opportunities for successful inoculant formulations. This review provides an overview of the interplay between nutrient availability and disease suppression governed by rhizobacteria in soil followed by the role of synthetic bacterial communities in developing efficient microbial inoculants. Moreover, an outlook on the beneficial activities of rhizobacteria in modifying soil characteristics to sustainably boost agroecosystem functioning is also provided.     

Eco-physiological and Biochemical Responses of Rapeseed (Brassica napus L.) to Abiotic Stresses: Consequences and Mitigation Strategies

Rapeseed yield parameters have been altered due to the increased exposure to abiotic stresses. The changing climatic conditions have reduced biomass production and seed yield, which ultimately affect the success of rapeseed crops. The severity and ability of abiotic stresses to act in tandem are a growing concern for agriculture producers across the globe. Rapeseed is one of the most vital cultivars in the world, serving as a major player in edible oil production. Abiotic stress conditions impose various effects on plant metabolism associated with growth stages, soil water storage capacity and plant physiological aspects. Modern agriculture aims to increased plant productivity to ensure global food security for the future. This can be achieved using quality seed, appropriate agricultural practices, measuring pest reduction techniques and understanding crop production challenges. Important tools, including conventional breeding and biotechnological approaches, can be employed to develop abiotic stress tolerance rapeseed. This review highlights the physiological and biochemical responses of rapeseed to abiotic stresses. The review also addresses conventional and modern stress mitigation strategies for the development of climate-smart rapeseed.

     

Enhancing drought tolerance in C(4) crops

Adaptation to abiotic stresses is a quantitative trait controlled by many different genes. Enhancing the tolerance of crop plants to abiotic stresses such as drought has therefore proved to be somewhat elusive in terms of plant breeding. While many C(4) species have significant agronomic importance, most of the research effort on improving drought tolerance has focused on maize. Ideally, drought tolerance has to be achieved without penalties in yield potential. Possibilities for success in this regard are highlighted by studies on maize hybrids performed over the last 70 years that have demonstrated that yield potential and enhanced stress tolerance are associated traits. However, while our understanding of the molecular mechanisms that enable plants to tolerate drought has increased considerably in recent years, there have been relatively few applications of DNA marker technologies in practical C(4) breeding programmes for improved stress tolerance. Moreover, until recently, targeted approaches to drought tolerance have concentrated largely on shoot parameters, particularly those associated with photosynthesis and stay green phenotypes, rather than on root traits such as soil moisture capture for transpiration, root architecture, and improvement of effective use of water. These root traits are now increasingly considered as important targets for yield improvement in C(4) plants under drought stress. Similarly, the molecular mechanisms underpinning heterosis have considerable potential for exploitation in enhancing drought stress tolerance. While current evidence points to the crucial importance of root traits in drought tolerance in C(4) plants, shoot traits may also be important in maintaining high yields during drought.     

Abiotic stress tolerance and competition‐related traits underlie phylogenetic clustering in soil bacterial communities

Soil bacteria typically coexist with close relatives generating widespread phylogenetic clustering. This has been ascribed to the abiotic filtering of organisms with shared ecological tolerances. Recent theoretical developments suggest that competition can also explain the phylogenetic similarity of coexisting organisms by excluding large low‐competitive clades. We propose that combining the environmental patterns of traits associated with abiotic stress tolerances or competitive abilities with phylogeny and abundance data, can help discern between abiotic and biotic mechanisms underlying the coexistence of phylogenetically related bacteria. We applied this framework in a model system composed of interspersed habitats of highly contrasted productivity and comparatively dominated by biotic and abiotic processes, i.e. the plant patch‐gap mosaic typical of drylands. We examined the distribution of 15 traits and 3290 bacterial taxa in 28 plots. Communities showed a marked functional response to the environment. Conserved traits related to environmental stress tolerance (e.g. desiccation, formation of resistant structures) were differentially selected in either habitat, while competition related traits (e.g. organic C consumption, formation of nutrient‐scavenging structures) prevailed under high resource availability. Phylogenetic clustering was stronger in habitats dominated by biotic filtering, suggesting that competitive exclusion of large clades might underlie the ecological similarity of co‐occurring soil bacteria.     

Biotechnological advancement in genetic improvement of broccoli (<Emphasis Type="Italic">Brassica oleracea</Emphasis> L. var. <Emphasis Type="Italic">italica</Emphasis>), an important vegetable crop

With the advent of molecular biotechnology, plant genetic engineering techniques have opened an avenue for the genetic improvement of important vegetable crops. Vegetable crop productivity and quality are seriously affected by various biotic and abiotic stresses which destabilize rural economies in many countries. Moreover, absence of proper post-harvest storage and processing facilities leads to qualitative and quantitative losses. In the past four decades, conventional breeding has significantly contributed to the improvement of vegetable yields, quality, post-harvest life, and resistance to biotic and abiotic stresses. However, there are many constraints in conventional breeding, which can only be overcome by advancements made in modern biology. Broccoli (Brassica oleracea L. var. italica) is an important vegetable crop, of the family Brassicaceae; however, various biotic and abiotic stresses cause enormous crop yield losses during the commercial cultivation of broccoli. Thus, genetic engineering can be used as a tool to add specific characteristics to existing cultivars. However, a pre-requisite for transferring genes into plants is the availability of efficient regeneration and transformation techniques. Recent advances in plant genetic engineering provide an opportunity to improve broccoli in many aspects. The goal of this review is to summarize genetic transformation studies on broccoli to draw the attention of researchers and scientists for its further genetic advancement.     

New frontiers in agriculture productivity: Optimised microbial inoculants and in situ microbiome engineering

Increasing agricultural productivity is critical to feed the ever-growing human population. Being linked intimately to plant health, growth and productivity, harnessing the plant microbiome is considered a potentially viable approach for the next green revolution, in an environmentally sustainable way. In recent years, our understanding of drivers, roles, mechanisms, along with knowledge to manipulate the plant microbiome, have significantly advanced. Yet, translating this knowledge to expand farm productivity and sustainability requires the development of solutions for a number of technological and logistic challenges. In this article, we propose new and emerging strategies to improve the survival and activity of microbial inoculants, including using selected indigenous microbes and optimising microbial delivery methods, as well as modern gene editing tools to engineer microbial inoculants. In addition, we identify multiple biochemical and molecular mechanisms and/approaches which can be exploited for microbiome engineering in situ to optimise plant-microbiome interactions for improved farm yields. These novel biotechnological approaches can provide effective tools to attract and maintain activities of crop beneficial microbiota that increase crop performance in terms of nutrient acquisition, and resistance to biotic and abiotic stresses, resulting in an increased agricultural productivity and sustainability.     

Inducing drought tolerance in plants: Recent advances

Undoubtedly, drought is one of the prime abiotic stresses in the world. Crop yield losses due to drought stress are considerable. Although a variety of approaches have been used to alleviate the problem of drought, plant breeding, either conventional breeding or genetic engineering, seems to be an efficient and economic means of tailoring crops to enable them to grow successfully in drought-prone environments. During the last century, although plant breeders have made ample progress through conventional breeding in developing drought tolerant lines/cultivars of some selected crops, the approach is, in fact, highly time-consuming and labor- and cost-intensive. Alternatively, marker-assisted breeding (MAB) is a more efficient approach, which identifies the usefulness of thousands of genomic regions of a crop under stress conditions, which was, in reality, previously not possible. Quantitative trait loci (QTL) for drought tolerance have been identified for a variety of traits in different crops. With the development of comprehensive molecular linkage maps, marker-assisted selection procedures have led to pyramiding desirable traits to achieve improvements in crop drought tolerance. However, the accuracy and preciseness in QTL identification are problematic. Furthermore, significant genetic × environment interaction, large number of genes encoding yield, and use of wrong mapping populations, have all harmed programs involved in mapping of QTL for high growth and yield under water limited conditions. Under such circumstances, a transgenic approach to the problem seems more convincing and practicable, and it is being pursued vigorously to improve qualitative and quantitative traits including tolerance to biotic and abiotic stresses in different crops. Rapid advance in knowledge on genomics and proteomics will certainly be beneficial to fine-tune the molecular breeding and transformation approaches so as to achieve a significant progress in crop improvement in future. Knowledge of gene regulation and signal transduction to generate drought tolerant crop cultivars/lines has been discussed in the present review. In addition, the advantages and disadvantages as well as future prospects of each breeding approach have also been discussed.     

Halophytes as a source of genes for abiotic stress tolerance

Agricultural productivity is majorly impacted due to various abiotic stresses, particularly salinity and drought. Halophytes serve as an excellent resource for identifying and developing new crop systems, as these grow very luxuriously in very high saline soils. Understanding salinity stress tolerance mechanisms in such plants is an important step towards generating crop varieties that can cope with environmental stresses. Use of modern tools of ‘omics’ analyses and small RNA sequencing has helped to gain insights into the complex plant stress responses. Salinity tolerance being a multigenic trait requires a combination of strategies and techniques to successfully develop improved crops varieties. Many transgenic crops are being developed through genetic transformation. Besides marker-assisted breeding/QTL approaches are also being used to improve abiotic stress tolerance. In this review, we focus on the recent developments in the utilization of halophytes as a source of genes for genetic improvement in abiotic stress tolerance of crops.     

The development and application of molecular markers for abiotic stress tolerance in barley

This article represents some current thinking and objectives in the use of molecular markers to abiotic stress tolerance. Barley has been chosen for study as it is an important crop species, as well as a model for genetic and physiological studies. It is an important crop and, because of its well-studied genetics and physiology, is an excellent candidate in which to devise more efficient breeding methods. Abiotic stress work on cultivated gene pools of small grain cereals frequently shows that adaptive and developmental genes are strongly associated with responses. Developmental genes have strong pleiotropic effects on a number of performance traits, not just abiotic stresses. One concern is that much of the genetic variation for improving abiotic stress tolerance has been lost during domestication, selection and modern breeding, leaving pleiotropic effects of the selected genes for development and adaptation. Such genes are critical in matching cultivars to their target agronomic environment, and since there is little leverage in changing these, other sources of variation may be required. In barley, and many other crops, greater variation to abiotic stresses exists in primitive landraces and related wild species gene pools. Wild barley, Hordeum spontaneum C. Koch is the progenitor of cultivated barley, Hordeum vulgare L. and is easily hybridized to H. vulgare. Genetic fingerprinting of H. spontaneum has revealed genetic marker associations with site-of-origin ecogeographic factors and also experimentally imposed stresses. Genotypes and collection sites have been identified which show the desired variation for particular stresses. Doubled haploid and other segregating populations, including landrace derivatives have been used to map genetically the loci involved. These data can be used in molecular breeding approaches to improve the drought tolerance of barley. One strategy involves screening for genetic markers and physiological traits for drought tolerance, and the associated problem of drought relief-induced mildew susceptibility in naturally droughted fields of North Africa.     

豆科牧草基因工程研究进展

豆科牧草既是重要的饲料作物,又在土壤改良、水土保持,以及生态环境保护方面发挥着积极作用。随着分子生物学和植物转化技术的发展和改进,通过基因工程技术对豆科牧草进行改良和培育已成为可能。本文就近几年来基因工程技术在各种豆科牧草的高产、抗病虫害、抗逆及品质改良等方面的研究进展进行了较全面的综述。 Progress in the Biotechnology of Legume Forage Plants ZHANG Zhen-xia1,2,FU Yi-kun1,CHU Cheng-cai2 1.College of Tasture,Gansu Agricultural University,Lanzhou 730070,China; 2.Institute of Genetics and Developmental Biology,Chinese Academy of Sciences,Beijing 100101,China Abstract:As important forage crops,legume forage plants can play an important role in improving natural environment,maintenins water and soil.With development of molecular biology and improvement of plant transformation techniques,molecular breeding of legume forage plants by biotechnology is possible.This review summarized recent progress on improvement of several forage crops,including improvement of nutrient quality,increase of biomass,enhancement of the assimilation and efficient absorb of nutrient element,and enhancement of abiotic and biotic stress resistance. Key words：legume forage plants; transgene; progress     

Synthetic hexaploid wheat enhances variation and adaptive evolution of bread wheat in breeding processes

Synthetic hexaploid wheat (SHW) that combines novel and elite genes from the tetraploid wheat Triticum turgidum L. and wild ancestor Aegilops tauschii Coss., has been used to genetically improve hexaploid common wheat. The abundant genetic diversity in SHW can effectively make breakthroughs in wheat genetic improvement through the inclusion of increased variation. In this paper, we reviewed the current advances in research and utilization of the primary SHW lines and SHW-derived wheat varieties that have enhanced evolution of modern wheat under conditions of natural and artificial selection in southwestern China. Using primary SHW lines, four high-yielding wheat varieties have been developed. In addition, using the SHW-derived varieties as breeding parents, 12 new wheat varieties were also developed. Results of genotype–phenotype and fingerprint analysis showed that the introgressed alleles from SHW lines have contributed a great number of elite characters to the new wheat varieties, and these elite characters include disease resistance, more spikes per plant, more grains per spike, larger grains, and higher grain-yield potential. We found that the primary SHW lines and SHW-derived varieties have identifiable effects to enhance genetic variation and adaptive evolution of modern hexaploid wheat, which significantly increased the grain yields of hexaploid wheat in recent years. These findings have significant implications in the breeding of high-yielding wheat varieties resistant to biotic and abiotic stresses using SHW as genetic resources.