Abiotic stresses including drought are serious threats to the sustainability of crop yields accounting for more crop productivity losses than any other factor in rainfed agriculture. Success in breeding for better adapted varieties to abiotic stresses depend upon the concerted efforts by various research domains including plant and cell physiology, molecular biology, genetics, and breeding. Use of modern molecular biology tools for elucidating the control mechanisms of abiotic stress tolerance, and for engineering stress tolerant crops is based on the expression of specific stress-related genes. Hence, genetic engineering for developing stress tolerant plants, based on the introgression of genes that are known to be involved in stress response and putative tolerance, might prove to be a faster track towards improving crop varieties. Far beyond the initial attempts to insert "single-action" genes, engineering of the regulatory machinery involving transcription factors has emerged as a new tool now for controlling the expression of many stress-responsive genes. Nevertheless, the task of generating transgenic cultivars is not only limited to the success in the transformation process, but also proper incorporation of the stress tolerance. Evaluation of the transgenic plants under stress conditions, and understanding the physiological effect of the inserted genes at the whole plant level remain as major challenges to overcome. This review focuses on the recent progress in using transgenic technology for the improvement of abiotic stress tolerance in plants. This includes discussion on the evaluation of abiotic stress response and the protocols for testing the transgenic plants for their tolerance under close-to-field conditions.

Water deficit is the major abiotic constraint affecting crop productivity in peanut (Arachis hypogaea L.). Water use efficiency under drought conditions is thought to be one of the most promising traits to improve and stabilize crop yields under intermittent water deficit. A transcription factor DREB1A from Arabidopsis thaliana, driven by the stress inducible promoter from the rd29A gene, was introduced in a drought-sensitive peanut cultivar JL 24 through Agrobacterium tumefaciens-mediated gene transfer. The stress inducible expression of DREB1A in these transgenic plants did not result in growth retardation or visible phenotypic alterations. T3 progeny of fourteen transgenic events were exposed to progressive soil drying in pot culture. The soil moisture threshold where their transpiration rate begins to decline relative to control well-watered (WW) plants and the number of days needed to deplete the soil water was used to rank the genotypes using the average linkage cluster analysis. Five diverse events were selected from the different clusters and further tested. All the selected transgenic events were able to maintain a transpiration rate equivalent to the WW control in soils dry enough to reduce transpiration rate in wild type JL 24. All transgenic events except one achieved higher transpiration efficiency (TE) under WW conditions and this appeared to be explained by a lower stomatal conductance. Under water limiting conditions, one of the selected transgenic events showed 40% higher TE than the untransformed control.

An efficient procedure for obtaining transgenicBrassica napus plants usingAgrobacterium binary vectors is described. The target tissue for the transformation is the cut end of cotyledonary petioles. These tissues, when cultured with their lamina intact, show a regeneration frequency of more than 80%. The cells of this cut surface, which undergo organogenesis, are very susceptible to topical infection byAgrobacterium. The cocultivation method used does not require feeder layers or use of exogenously applied promoters of virulence. After 72h of infection withAgrobacterium the explants were transferred to selective regeneration medium. Using kanamycin (15μg cm(-3)) for selection, transgenic plantlets emerged within 3 weeks. These plantlets which appeared on over half the explants were excised and rooted for a further 7-10 days. When the plants were large enough, leaves were taken for assay of NPT II activity using dot blots. Most of the plants surviving the selection showed substantial NPT II activity. The frequency of transformation and yield of transgenic plants was higher than in previously reported methods with this species. Southern blotting revealed that integration of the T-DNA frequently occurred in multiple copies and at multiple loci in the genome. The transgenicB. napus plants all grew normally and developed fertile flowers. The transgenic plants were self-pollinated and their progeny studied by two methods. The first was a single-embryo NPT II assay performed on developing seeds of these selfed-plants. The second was a leaf bleaching assay performed by selection of germinating seedlings of the selfed progeny. Both assays yielded segregation ratios consistent with the number of integration events indicated by Southern blots. The method should have broad application in studies of gene expression in theBrassicaceae and will be a cost-effective alternative to those seeking to improveBrassica crops by introduction of foreign genes.

Cotyledon explants from mature peanut seeds (Arachis hypogaea L.) were optimized to obtain adventitious shoot buds with high frequencies (>90%). Efficient transformation of these cotyledons by using Agrobacterium tumefaciens strain C58 carrying neomycin phosphotransferase II (nptII) and ß-glucuronidase (GUS; uidA), or coat protein gene of the Indian peanut clump virus (IPCVcp) and nptII on binary vectors (pBI121; pROKII:IPCVcp) led to the production of a large percentage (55%) of transgenic plants. Transformed individuals were obtained through selection on medium containing 125 mg l(-1) kanamycin. A large number of independently transformed plants (over 75) were successfully transplanted to the glasshouse. Integration of the transgenes and stable genetic transformants in the progeny were assessed by PCR amplification of 700-bp fragment of nptII and 585-bp of IPCVcp genes, and Southern blot hybridizations in the T1 generation of transgenic plants. Analysis of 35 transgenic plants of T1 generation from the progeny of a single transformation event suggested the segregation of a single copy insert in a 3:1 Mendelian ratio. On an average, 120-150 days were required between the initiation of explant transformation and transfer of rooted plants to the greenhouse. The cotyledon regeneration system proved to be an excellent vehicle for the production of a large number of independently transformed peanut plants. Shoot formation was rapid and prolific, and a large proportion of these shoots developed into fertile plants. The method reported here provides new opportunities for the crop improvement of peanut via genetic transformation.

a b s t r a c tAflatoxins are toxic, carcinogenic, mutagenic, teratogenic and immunosuppressive byproducts of Aspergillus spp. that contaminate a wide range of crops such as maize, peanut, and cotton. Aflatoxin not only affects crop production but renders the produce unfit for consumption and harmful to human and livestock health, with stringent threshold limits of acceptability. In many crops, breeding for resistance is not a reliable option because of the limited availability of genotypes with durable resistance to Aspergillus. Understanding the fungal/crop/environment interactions involved in aflatoxin contamination is therefore essential in designing measures for its prevention and control. For a sustainable solution to aflatoxin contamination, research must be focused on identifying and improving knowledge of host-plant resistance factors to aflatoxin accumulation. Current advances in genetic transformation, proteomics, RNAi technology, and marker-assisted selection offer great potential in minimizing preharvest aflatoxin contamination in cultivated crop species. Moreover, developing effective phenotyping strategies for transgenic as well as precision breeding of resistance genes into commercial varieties is critical. While appropriate storage practices can generally minimize post-harvest aflatoxin contamination in crops, the use of biotechnology to interrupt the probability of pre-harvest infection and contamination has the potential to provide sustainable solution.

Nitric oxide (NO) is a versatile gaseous signaling molecule with increasing significance in plant research due to its association with various stress responses. Although, improved drought tolerance by NO is associated greatly with its ability to reduce stomatal opening and oxidative stress, it can immensely influence other physiological processes such as photosynthesis, proline accumulation and seed germination under water deficit. NO as a free radical can directly alter proteins, enzyme activities, gene transcription, and post-translational modifications that benefit functional recovery from drought. The present drought-mitigating strategies have focused on exogenous application of NO donors for exploring the associated physiological and molecular events, transgenic and mutant studies, but are inadequate. Considering the biphasic effects of NO, a cautious deployment is necessary along with a systematic approach for deciphering positively regulated responses to avoid any cytotoxic effects. Identification of NO target molecules and in-depth analysis of its effects under realistic field drought conditions should be an upmost priority. This detailed synthesis on the role of NO offers new insights on its functions, signaling, regulation, interactions and co-existence with different drought-related events providing future directions for exploiting this molecule towards improving drought tolerance in crop plants.

We have isolated a novel member of the TNFR family, designated TAJ, that is highly expressed during embryonic development. TAJ possesses a unique cytoplasmic domain with no sequence homology to the previously characterized members of the TNFR family. TAJ interacts with the TRAF family members and activates the JNK pathway when overexpressed in mammalian cells. Although it lacks a death domain, TAJ is capable of inducing apoptosis by a caspase-independent mechanism. Based on its unique expression profile and signaling properties, TAJ may play an essential role in embryonic development.

Recombinant DNA technology has significantly augmented the conventional crop improvement, and has a great promise to assist plant breeders to meet the increased food demand predicted for the 21st century. Dramatic progress has been made over the past two decades in manipulating genes from diverse and exotic sources, and inserting them into microorganisms and crop plants to confer resistance to insect pests and diseases, tolerance to herbicides, drought, soil salinity and aluminum toxicity; improved post-harvest quality; enhanced nutrient uptake and nutritional quality; increased photosynthetic rate, sugar, and starch production; increased effectiveness of biocontrol agents; improved understanding of gene action and metabolic pathways; and production of drugs and vaccines in crop plants. Despite the diverse and widespread beneficial applications of biotechnology products, there remains a critical need to present these benefits to the general public in a real and understandable way that stimulates an unbiased and responsible public debate. The development, testing and release of agricultural products generated through biotechnology-based processes should be continuously optimized based on the most recent experiences. This will require a dynamic and streamlined regulatory structure, clearly supportive of the benefits of biotechnology, but highly sensitive to the well being of humans and environment.