Development Of Crop Cultivars Research Articles

Functional characterization and regulatory mechanism of wheat CPK34 kinase in response to drought stress

BackgroundDrought is one of the most adverse environmental factors limiting crop productions and it is important to identify key genetic determinants for food safety. Calcium-dependent protein kinases (CPKs) are known to be involved in plant growth, development, and environmental stresses. However, biological functions and regulatory mechanisms of many plant CPKs have not been explored. In our previous study, abundance of the wheat CPK34 (TaCPK34) protein was remarkably upregulated in wheat plants suffering from drought stress, inferring that it could be involved in this stress. Therefore, here we further detected its function and mechanism in response to drought stress.ResultsTranscripts of the TaCPK34 gene were significantly induced after PEG-stimulated water deficiency (20% PEG6000) or 100 μM abscisic acid (ABA) treatments. The TaCPK34 gene was transiently silenced in wheat genome by using barley stripe mosaic virus-induced silencing (BSMV-VIGS) method. After 14 days of drought stress, the transiently TaCPK34-silenced wheat seedlings showed more sensitivity compared with control, and the plant biomasses and relative water contents significantly decreased, whereas soluble sugar and MDA contents increased. The iTRAQ-based quantitative proteomics was employed to measure the protein expression profiles in leaves of the transiently TaCPK34-silenced wheat plants after drought stress. There were 6103 proteins identified, of these, 51 proteins exhibited significantly altered abundance, they were involved in diverse function. And sequence analysis on the promoters of genes, which encoded the above identified proteins, indicated that some promoters harbored some ABA-responsive elements. We determined the interactions between TaCPK34 and three identified proteins by using bimolecular fluorescent complementation (BiFC) method and our data indicated that TaCPK34directly interacted with the glutathione S-transferase 1 and prx113, respectively.ConclusionsOur study suggested that the TaCPK34 gene played positive roles in wheat response to drought stress through directly or indirectly regulating the expression of ABA-dependent manner genes, which were encoding identified proteins from iTRAQ-based quantitative proteomics. And it could be used as one potential gene to develop crop cultivars with improved drought tolerance.

Genomic analysis of Spanish wheat landraces reveals their variability and potential for breeding

BackgroundOne of the main goals of the plant breeding in the twenty-first century is the development of crop cultivars that can maintain current yields in unfavorable environments. Landraces that have been grown under varying local conditions include genetic diversity that will be essential to achieve this objective. The Center of Plant Genetic Resources of the Spanish Institute for Agriculture Research maintains a broad collection of wheat landraces. These accessions, which are locally adapted to diverse eco-climatic conditions, represent highly valuable materials for breeding. However, their efficient use requires an exhaustive genetic characterization. The overall aim of this study was to assess the diversity and population structure of a selected set of 380 Spanish landraces and 52 reference varieties of bread and durum wheat by high-throughput genotyping.ResultsThe DArTseq GBS approach generated 10 K SNPs and 40 K high-quality DArT markers, which were located against the currently available bread and durum wheat reference genomes. The markers with known locations were distributed across all chromosomes with relatively well-balanced genome-wide coverage. The genetic analysis showed that the Spanish wheat landraces were clustered in different groups, thus representing genetic pools providing a range of allelic variation. The subspecies had a major impact on the population structure of the durum wheat landraces, with three distinct clusters that corresponded to subsp. durum, turgidum and dicoccon being identified. The population structure of bread wheat landraces was mainly biased by geographic origin.ConclusionsThe results showed broader genetic diversity in the landraces compared to a reference set that included commercial varieties, and higher divergence between the landraces and the reference set in durum wheat than in bread wheat. The analyses revealed genomic regions whose patterns of variation were markedly different in the landraces and reference varieties, indicating loci that have been under selection during crop improvement, which could help to target breeding efforts. The results obtained from this work will provide a basis for future genome-wide association studies.

Bio-chemicals triggering host preference mechanism against tomato fruit borer, Helicoverpa armigera (H�bner)

Mechanism of host plant resistance in tomato varieties was evaluated and compared against tomato fruit borer, Helicoverpa armigera (Hubner) attack in the Solan district known to be ‘Tomato bowl of Himachal Pradesh’. Eight varieties utilized for the experiment included three self pollinating indeterminate varieties developed by selection (Solan Lalima, Solan Vajar, Palam Pink) and four hybrids (Naveen 2000+, Heem Sohna, Red Gold, Rakshita Yash Tomato). In order to locate the sources for resistance in tomato foliage various macro and micro- nutrients were extracted from these varieties and chemical composition of tomato fruits viz., content of total phenols, titrable acidity, reducing sugars and total sugars were also estimated to compare for varying levels of resistance to Helicoverpa armigera . The content of phenol and sugars in tomato fruits was found to be negatively correlated with fruit infestation with values of correlation coefficient (r = - 0.895) and (r = - 0.650), respectively, indicating that susceptible varieties were low in phenols as well as in sugars. Nitrogen (r = 0.660), potassium (r = 0.679), magnesium (r = 0.698), iron (r = 0.547) and manganese (r = 0.546) content were found to be optimistically correlated with per cent fruit infestation while, phosphorous (r = - 0.857) and zinc (r = - 0.801) content did not favor the fruit borer attack. This observed resistance can be exploited for developing crop cultivars, which readily produce the inducible response upon mild infestation, and can act as important components of integrated pest management compatible with other approaches like biological control, cultural control as well as chemical control.

HvPAA1 Encodes a P-Type ATPase, a Novel Gene for Cadmium Accumulation and Tolerance in Barley (Hordeum vulgare L.).

The identification of gene(s) that are involved in Cd accumulation/tolerance is vital in developing crop cultivars with low Cd accumulation. We developed a doubled haploid (DH) population that was derived from a cross of Suyinmai 2 (Cd-sensitive) × Weisuobuzhi (Cd-tolerant) to conduct quantitative trait loci (QTL) mapping studies. We assessed chlorophyll content, traits that are associated with development, metal concentration, and antioxidative enzyme activity in DH population lines and parents under control and Cd stress conditions. A single QTL, designated as qShCd7H, was identified on chromosome 7H that was linked to shoot Cd concentration; qShCd7H explained 17% of the phenotypic variation. Comparative genomics, map-based cloning, and gene silencing were used in isolation, cloning, and functional characterization of the candidate gene. A novel gene HvPAA1, being related to shoot Cd concentration, was identified from qShCd7H. Sequence comparison indicated that HvPAA1 carried seven domains with an N-glycosylation motif. HvPAA1 is predominantly expressed in shoots. Subcellular localization verified that HvPAA1 is located in plasma membrane. The silencing of HvPAA1 resulted in growth inhibition, greater Cd accumulation, and a significant decrease in Cd tolerance. We conclude HvPAA1 is a novel plasma membrane-localized ATPase that contributes to Cd tolerance and accumulation in barley. The results provide us with new insights that may aid in the screening and development of Cd-tolerant and low-Cd-accumulation crops.

MiR164c and miR168a regulate seed vigor in rice.

MicroRNAs (miRNAs) are key regulators of gene expression in many important biological processes of plants. However, few miRNAs have been shown to regulate seed vigor. Here, we conducted microarray assays to analyze miRNA expression levels in seeds of the rice (Oryza sativa L.) cultivar ZR02. Results showed significant differences in the expression of 11 miRNAs between artificially aged and untreated control seeds. Among these, osa-miR164c was transcriptionally upregulated, while osa-miR168a was downregulated in artificially aged seeds; this was verified by quantitative real-time PCR analysis. Under the same aging condition, osa-miR164c overexpression in OE164c transgenic seeds and osa-miR168a silencing in MIM168a transgenic seeds of the rice cultivar Kasalath led to lower germination rates, whereas osa-miR164c silencing in MIM164c and osa-miR168a overexpression in OE168a resulted in higher seed germination rates compared with wild-type seeds. Meanwhile, changes in cytomembrane permeability of seeds and in the expression level of osa-miR164c target genes (OsPM27 and OsPSK5) and osa-miR168a target genes (OsAGO1 and OsPTR2) under aging conditions coincided with changes in seed vigor induced by osa-miR164c and osa-miR168a. Thus, genetic manipulation of miRNAs has important implications in the development of crop cultivars with high vigor and extended life span of seeds.

Breeding for increased drought tolerance in wheat: a review

Drought, being a yield-limiting factor, has become a major threat to international food security. It is a complex process, and drought tolerance response is carried out by various genes, transcription factors, microRNAs, hormones, proteins, co-factors, ions and metabolites. This complexity has limited the development of crop cultivars for drought tolerance. Breeding for drought tolerance is further complicated because several types of abiotic stress, such as high temperatures, high irradiance, and nutrient toxicities or deficiencies, can challenge crop plants simultaneously. Although marker-assisted selection is now widely deployed in wheat, it has not contributed significantly to cultivar improvement for adaptation to low-yielding environments, and breeding has relied largely on direct phenotypic selection for improved performance in these difficult environments. Advances in plant breeding to produce improved and higher performing wheat cultivars are key to making dryland food-production systems more efficient and more resistant to pressure from drought, extremes of cold and heat, unpredictable rainfall, and new pests and diseases. For optimal performance, wheat cultivars can be targeted to specific farming systems, depending on local conditions and stresses. Genetic gain in wheat yield potential during the last century has been achieved by plant breeding and is well documented. It has been studied by comparing, in the same field trial, the yield of cultivars characterised by different years of release. Genomic selection (GS) and high-throughput phenotyping (HTP) have attracted the interest of plant breeders, and both approaches promise to revolutionise the prediction of complex traits, including growth, yield and adaptation to stress. This review describes the impact of drought on yield, trends in yield for boosting crop yields to meet the projected demands of rising global population by 2050, and genetic gain achieved by plant breeding in the last decades; and gathers known functional information on the genes, metabolites and traits and their direct involvement in conferring drought tolerance in wheat. In addition, it discusses recently developed techniques (i.e. GS and HTP) integrated with approaches such as breeding, genetics, genomics, and agronomic strategies for improving drought in wheat.

Biochemical basis ofplant-insect interaction in arid horticulture crops: a scientific review

Plants are persistently confronted to both abiotic and biotic stresses that drastically reduce their productivity. Plant responses to these stresses are multifaceted and involve copious Biochemical, physiological, molecular, molecular and cellular adaptations. Recent evidence shows that simultaneous occurrence of abiotic and biotic stress can have a positive effect on plant performance by reducing the susceptibility to biotic stress which is a positive sign for arid horticulture crops. Some of these adaptations specifically biochemical adaptations become the source of plant defense mechanisms against biotic stresses like insect’s pest and diseases. These biochemical adaptations/mechanisms includes production of secondary metabolites of plant defense against the biotic stresses especially against insects are wide spread and highly dynamic, and are mediated the response directly or indirectly in arid horticultural crops. Production of secondary metabolites viz. terpenes, phenolics, flavonoids, alkaloids, N & S containing compounds is constitutive as well as inducible through mild stress caused by insect damage to plants which leads to affect the feeding, growth and survival of the insect. Quality and quantity of constitutive secondary metabolites production is species as well as cultivar specific and can be expressed as signature of particular plant or species and leads to the phenomenon of host-plant interaction or host-plant resistance. This phenomenon of host plant resistance to insect can be exploited for development of crop cultivars which readily produce the inducible response upon mild infestation and can perform as one of the of integrated pest management for sustainable arid horticulture crop production. This review presents overviews about these constitutive and inducible responses towards biochemical adaptations in arid horticulture crops to protect themselves against insects.

Impact of heat-wave at high and low VPD on photosynthetic components of wheat and their recovery

Indirect effects of high temperature through increased vapor pressure deficit (VPD) are vital but often ignored in climate impact studies. We investigated the direct (via heat) and indirect (via VPD) effects of a post-anthesis applied high temperature episode on biochemical and diffusional components of photosynthesis in two wheat cultivars. Plants were exposed to a five-day episode of hot humid (HH: 36 °C; 1.96 kPa) or hot dry (HD: 36 °C; 3.92 kPa) climate, including normal climate (NC: 24 °C; 1.49 kPa VPD) as control. The capacity and sensitivity of different photosynthetic components that included diffusional and biochemical processes was investigated both during the stress and after six-days of recovery under NC. The results showed that, regardless of VPD, photosynthetic capacity under high temperature was largely impaired by biochemical limitations while the diffusional limitations were relatively insignificant. The processes involved in CO2-use (i.e. in vivo carboxylation efficiency and Vcmax) presented higher sensitivity than the processes involved in light-use (PSII efficiency, quantum yield and chlorophyll content index). Maximum photosynthetic capacity under high temperature was primarily restricted by limitations to RuBP-regeneration. Effects of higher VPD through diffusional limitations (stomatal and mesophyll conductance) were potentially insignificant. The effects of VPD through changes in transpiration were observed under HH, where significantly higher gs and increase in gs (and transpiration) over time due to acclimation led to drought, because the irrigation amounts per day remained same over the stress period. Resultantly, the photosynthesis under HH was co-limited by both RuBP-carboxylation and RuBP-regeneration. Irrespective of VPD, the after-effects of heat-wave were either non-existent or potentially insignificant, as most of the photosynthetic and related parameters recovered to their respective control. The results indicated that the effect of VPD through changes in soil moisture dynamics is an important confounding variable to consider in climate-impact studies. Higher sensitivity of CO2-use suggested that even moderately high temperature-episodes might limit photosynthetic capacity and hence crop productivity, thus reiterating the need to develop crop cultivars with greater tolerance to high temperatures.

Thermosensing Enlightened.

Understanding the molecular networks driving plant responses to high ambient temperatures is crucial for developing crop cultivars resistant to global warming. Although several factors involved in temperature signalling are known, a thermosensing mechanism had remained elusive. However, two recent publications demonstrate that the photoreceptor phytochrome B (phyB) also acts as a thermosensor.

Review Paper on Approaches in Developing Inbred Lines in Cross-Pollinated Crops

Plant breeding aims to constantly develop crop cultivars with improved yields and quality and tolerant to droughts, diseases and pests. Use of genetically improved crop cultivars and better management practices are among the best strategies to increase food production and meet a projected doubling of food demand. Inbred lines are homozygous genotypes produced by repeated selfing with selection over several generations. It is developed and maintained by repeated selfing of selected plants. In cross-pollinated species with strongly expressed self-incompatibility, various techniques are used to overcome the incompatibility. The technique of doubled haploids may be used to produce complete homozygous diploid lines in just 1 year (versus more than 4 years in conventional breeding) by doubling the chromosome complement of haploid cells. Doubled haploidy is and will continue to be a very efficient tool for the production of completely homozygous lines from heterozygous donor plants in a single step. Haploids contain half the chromosome number of somatic cells. Anthers/stigma Contain immature microspores or pollen grains with the haploid (n) chromosome number. If successfully cultured (anther culture), the plantlets resulting will have a haploid genotype. To have maximum genetic variability in the plantlets, breeders usually use anthers from F1 or F2 plants. Usually, the haploid plant is not the goal of anther culture. Rather, the plantlets are diplodized (to produce diploid plants) by using colchicine for chromosome doubling. This strategy yields a highly inbred line that is homozygous at all loci, after just one generation.

Gen dan QTL Pengendali Toleransi Tanaman terhadap Keracunan Aluminium dan Aplikasinya untuk Pemuliaan Tanaman di Indonesia

<p>Genetic knowledge of loci controlling Al toxicity tolerance is the key for a successful breeding program in developing Al<br />tolerant cultivars. Tolerance level of crop plants to Al toxicity is genetically controlled. The gene inheritance pattern is mainly<br />resulted from intensive studies of cereal crops, such as wheat, sorghum, maize, and rice. The trait can be controlled by a<br />single dominant gene, a single dominant gene with many alleles, a pair of dominant genes, or by many genes (QTL). The<br />majority of the Al tolerance genes identified so far belongs to two independent groups of gene families, i.e. aluminumactivated<br />malate transporter (ALMT) and multidrug and toxic compound extrusion (MATE), both encoding transport proteins<br />involved in Al-activated organic acid release, mainly citrate and malate. The variations in Al toxicity tolerance phenotypes are<br />strongly correlated with the expressions of such genes in the root apical cells. Many Al tolerance QTLs have been mapped in<br />the genomes of various crop species and were found to be colocated with the ALMT and MATE genes. The genetic maps of<br />the Al tolerance genes and QTLs facilitate breeding programs for developing Al-tolerant cultivars through marker-assisted<br />breeding methods. Al tolerance genes that have been isolated from genetically unrelated species can be used in genetic<br />transformation studies of crop genotypes sexually incompatible to the gene source genotypes. The application of these<br />molecular breeding methods expedites breeding programs to develop crop cultivars tolerance to Al toxicity and acid soils.<br />Genomic technologies by using next-generation sequencing and high-throughput genotyping system accelerate Al toxicity<br />tolerance gene and QTL discoveries of various crop species. The modern genomic technologies also facilitate more<br />comprehensive PGR characterization and utilization to accelerate identification and isolation of the Al tolerance genes and<br />QTLs to be used in a more comprehensive breeding program to support national food self sufficiency and food security<br />programs.</p>

Untapping root system architecture for crop improvement.

Drought leads to greater yield loss in crops than any other abiotic stress. Roots form a plant’s first line of defense against water deficit, and in this issue Gao and Lynch (pages 4533–4546) report that fewer but longer crown roots facilitate water acquisition from subsoil and thus improve drought tolerance in maize. Roots are the first organ to sense water deficit, and at the same time they extract virtually all those mineral nutrients from soil that are consumed by humans. Soil resource acquisition under challenging conditions such as drought is a primary limitation on plant productivity, resulting in low yields and thus food insecurity in the poorest countries. Indeed, in overall global agriculture, drought accounts for more loss in plant productivity than any other abiotic factor. Thus the development of crop cultivars with enhanced traits for soil resource acquisition is a key goal for feeding the growing world population (Lynch, 2007). However, so far the potential of root traits for crop improvement remains largely unexploited, largely because of the limited accessibility of roots in their belowground soil habitat.

A remorin gene is implicated in quantitative disease resistance in maize.

Quantitative disease resistance is used by plant breeders to improve host resistance. We demonstrate a role for a maize remorin ( ZmREM6.3 ) in quantitative resistance against northern leaf blight using high-resolution fine mapping, expression analysis, and mutants. This is the first evidence of a role for remorins in plant-fungal interactions. Quantitative disease resistance (QDR) is important for the development of crop cultivars and is particularly useful when loci also confer multiple disease resistance. Despite its widespread use, the underlying mechanisms of QDR remain largely unknown. In this study, we fine-mapped a known quantitative trait locus (QTL) conditioning disease resistance on chromosome 1 of maize. This locus confers resistance to three foliar diseases: northern leaf blight (NLB), caused by the fungus Setosphaeria turcica; Stewart's wilt, caused by the bacterium Pantoea stewartii; and common rust, caused by the fungus Puccinia sorghi. The Stewart's wilt QTL was confined to a 5.26-Mb interval, while the rust QTL was reduced to an overlapping 2.56-Mb region. We show tight linkage between the NLB QTL locus and the loci conferring resistance to Stewart's wilt and common rust. Pleiotropy cannot be excluded for the Stewart's wilt and the common rust QTL, as they were fine-mapped to overlapping regions. Four positional candidate genes within the 243-kb NLB interval were examined with expression and mutant analysis: a gene with homology to an F-box gene, a remorin gene (ZmREM6.3), a chaperonin gene, and an uncharacterized gene. The F-box gene and ZmREM6.3 were more highly expressed in the resistant line. Transposon tagging mutants were tested for the chaperonin and ZmREM6.3, and the remorin mutant was found to be more susceptible to NLB. The putative F-box is a strong candidate, but mutants were not available to test this gene. Multiple lines of evidence strongly suggest a role for ZmREM6.3 in quantitative disease resistance.

Climate change and investment in agricultural research: Policy challenges in India

Agriculture will continue to be the major sector supporting the Indian economy. On the other hand, the reported and projected impact of climate change raises question against its sustainability and stability. The present paper through reviewing of the relevant literature therefore aims to address three interrelated issues. The first issue on climate change reflected that the annual temperature increase by 0.5°C during the period 1901–2003 and to counteract the negative impact of climate change, the farming community resorted to adaptation strategies, mainly adoption of resistant cultivars. Concerning this need, the Central Government initiated the mega project National Initiatives on Climate Research Agriculture (NICRA) with a budget of 200 crores during the year 2010–11 and the National Mission for Sustainable Agriculture (NMSA) scheme with a budget support of 1, 08, 000 crores in order to provide resilient to agriculture with one of the main components on the development of crop cultivars. Emphasizing the need for research in agriculture particularly under the climate change scenario the third issue on the status of Agricultural R&D investment in India was discussed and revealed that the level of Agricultural Research Indicator (ARI) is below the recommended level of 2% being only 0.43% during the year 2012–13. Meeting the need of the farming community coupled with the objectives of the mentioned Government initiatives and the target set to attain 2% of ARI during the twelve plan the study recommended that Agricultural R&D investment needs to be strengthened to maintain the viability of Indian agriculture.

CO2 Sensing and CO2 Regulation of Stomatal Conductance: Advances and Open Questions.

Guard cells form epidermal stomatal gas-exchange valves in plants and regulate the aperture of stomatal pores in response to changes in the carbon dioxide (CO2) concentration ([CO2]) in leaves. Moreover, the development of stomata is repressed by elevated CO2 in diverse plant species. Evidence suggests that plants can sense [CO2] changes via guard cells and via mesophyll tissues in mediating stomatal movements. We review new discoveries and open questions on mechanisms mediating CO2-regulated stomatal movements and CO2 modulation of stomatal development, which together function in the CO2 regulation of stomatal conductance and gas exchange in plants. Research in this area is timely in light of the necessity of selecting and developing crop cultivars that perform better in a shifting climate.

Towards plant salinity tolerance-implications from ion transporters and biochemical regulation

Crop production is adversely affected by soil salinization and therefore, development of crop cultivars with salt tolerance is crucial for better utilization of saline soil and enhancement of sustainable agricultural productivity. High salt concentration induces various physiological and biochemical responses in plants, while plants employ mechanisms in adaptation to salinity stress at cellular, metabolic and whole-plant levels, including stress signalling, ion balancing, osmotic regulation and antioxidant protection. In this review, we discuss the signalling pathways and key mechanisms of Na+ detoxification mediated by ion transporters and antiporters, and make an overview of practical strategies and methodologies for functional characterization of high-affinity potassium transporters. In addition, recent research advances in improvement of plant salt tolerance through biochemical regulation, particularly alleviating salt stress by exogenous application of gibberellins and nitric oxide, are reviewed. We also propose key research perspectives that remain to be addressed in future.

Carbon Dioxide Control in an Open System that Measures Canopy Gas Exchanges

Atmospheric carbon dioxide concentration ([CO2]) affects both C3 carbon net assimilation (A) as well as crop water use. Methods for measuring whole canopy gas exchange responses under [CO2] enrichment are needed for breeding programs aiming to develop crop cultivars resistant to stresses like drought in a future higher CO2 world. Previously we developed and tested a portable, open transparent chamber system for measuring canopy gas exchanges. Here we describe further development of this system by adding the capability of controlling [CO2]. Pure CO2 injection into the system was accomplished with a data logger operated mass flow controller attached to a high pressure CO2 gas cylinder. Across the full range of chamber air flow rates, [CO2] enrichment controls were within ± 12 µmol mol−1 of the desired set point. Following an abrupt user‐selected change in chamber air flow rate, [CO2] enrichment controls were re‐established within 3 to 5 min.

Iron biofortification of rice using different transgenic approaches.

More than 2 billion people suffer from iron (Fe) deficiency, and developing crop cultivars with an increased concentration of micronutrients (biofortification) can address this problem. In this review, we describe seven transgenic approaches, and combinations thereof, that can be used to increase the concentration of Fe in rice seeds. The first approach is to enhance the Fe storage capacity of grains through expression of the Fe storage protein ferritin under the control of endosperm-specific promoters. Using this approach, the concentration of Fe in the seeds of transformants was increased by approximately 2-fold in polished seeds. The second approach is to enhance Fe translocation by overproducing the natural metal chelator nicotianamine; using this approach, the Fe concentration was increased by up to 3-fold in polished seeds. The third approach is to enhance Fe influx to the endosperm by expressing the Fe(II)-nicotianamine transporter gene OsYSL2 under the control of an endosperm-specific promoter and sucrose transporter promoter, which increased the Fe concentration by up to 4-fold in polished seeds. The fourth approach is introduction of the barley mugineic acid synthesis gene IDS3 to enhance Fe uptake and translocation within plants, which resulted in a 1.4-fold increase in the Fe concentration in polished seeds during field cultivation. In addition to the above approaches, Fe-biofortified rice was produced using a combination of the first, second, and third approaches. The Fe concentration in greenhouse-grown T2 polished seeds was 6-fold higher and that in paddy field-grown T3 polished seeds was 4.4-fold higher than in non-transgenic seeds without any reduction in yield. When the first and fourth approaches were combined, the Fe concentration was greater than that achieved by introducing only the ferritin gene, and Fe-deficiency tolerance was observed. With respect to Fe biofortification, the introduction of multiple Fe homeostasis genes is more effective than the introduction of individual genes. Moreover, three additional approaches, i.e., overexpression of the Fe transporter gene OsIRT1 or OsYSL15, overexpression of the Fe deficiency-inducible bHLH transcription factor OsIRO2, and knockdown of the vacuolar Fe transporter gene OsVIT1 or OsVIT2, may be useful to further increase the Fe concentration of seeds.

Transgenic Tomato Plants Expressing BrOAT1 gene from Brassica rapa var. SUN-3061 Show Enhanced Tolerance to Salt Stress

Salt stress is by far the leading environmental stress limiting crop yields worldwide. Genetic engineering techniques hold great promise for developing crop cultivars with high tolerance to salt stress. In this study, the Brassica rapa var. SUN-3061 BrOAT1 gene was transferred into tomato through Agrobacterium-mediated leaf disc transformation. The transgenic status and transgene expression of the transgenic plants was confirmed by polymerase chain reaction (PCR) analysis and semi-quantitative one step RT-PCR analysis respectively. Subsequently, the growth status under salt stress, and physiological responses to salt stress of transgenic tomato were studied. The results showed that the transgenic plants exhibited better growth status under salt stress condition compared to the wild type plants. In physiological assessment of salt stress tolerance, transgenic plants showed more dry matter accumulation and maintained significantly higher levels of leaf chlorophyll content along with increasing levels of salt stress than the wild type plants. This study shows that BrOAT1 is a candidate gene in the engineering of crops for enhanced salt stress tolerance.

Water: the most important 'molecular' component of water stress tolerance research.

Water deficit is the main yield-limiting factor across the Asian and African semiarid tropics and a basic consideration when developing crop cultivars for water-limited conditions is to ensure that crop water demand matches season water supply. Conventional breeding has contributed to the development of varieties that are better adapted to water stress, such as early maturing cultivars that match water supply and demand and then escape terminal water stress. However, an optimisation of this match is possible. Also, further progress in breeding varieties that cope with water stress is hampered by the typically large genotype×environment interactions in most field studies. Therefore, a more comprehensive approach is required to revitalise the development of materials that are adapted to water stress. In the past two decades, transgenic and candidate gene approaches have been proposed for improving crop productivity under water stress, but have had limited real success. The major drawback of these approaches has been their failure to consider realistic water limitations and their link to yield when designing biotechnological experiments. Although the genes are many, the plant traits contributing to crop adaptation to water limitation are few and revolve around the critical need to match water supply and demand. We focus here on the genetic aspects of this, although we acknowledge that crop management options also have a role to play. These traits are related in part to increased, better or more conservative uses of soil water. However, the traits themselves are highly dynamic during crop development: they interact with each other and with the environment. Hence, success in breeding cultivars that are more resilient under water stress requires an understanding of plant traits affecting yield under water deficit as well as an understanding of their mutual and environmental interactions. Given that the phenotypic evaluation of germplasm/breeding material is limited by the number of locations and years of testing, crop simulation modelling then becomes a powerful tool for navigating the complexity of biological systems, for predicting the effects on yield and for determining the probability of success of specific traits or trait combinations across water stress scenarios.