Agrobacterium tumefaciens mediated transfer of Phaseolus vulgaris alpha-amylase inhibitor-1 gene into mungbean Vigna radiata (L.) Wilczek using bar as selectable marker

Recalcitrance to transformation, a hindrance for genome editing of legumes

Plant genome editing, a recently discovered method for targeted mutagenesis, has emerged as a promising tool for crop improvement and gene function research. Many genome-edited plants, such as rice, wheat, and tomato, have emerged over the last decade. As the preliminary steps in the procedure for genome editing involve genetic transformation, amenability to genome editing depends on the efficiency of genetic engineering. Hence, there are numerous reports on the aforementioned crops because they are transformed with relative ease. Legume crops are rich in protein and, thus, are a favored source of plant proteins for the human diet in most countries. However, legume cultivation often succumbs to various biotic/abiotic threats, thereby leading to high yield loss. Furthermore, certain legumes like peanuts possess allergens, and these need to be eliminated as these deprive many people from gaining the benefits of such crops. Further genetic variations are limited in certain legumes. Genome editing has the potential to offer solutions to not only combat biotic/abiotic stress but also generate desirable knock-outs and genetic variants. However, excluding soybean, alfalfa, and Lotus japonicus, reports obtained on genome editing of other legume crops are less. This is because, excluding the aforementioned three legume crops, the transformation efficiency of most legumes is found to be very low. Obtaining a higher number of genome-edited events is desirable as it offers the option to genotypically/phenotypically select the best candidate, without the baggage of off-target mutations. Eliminating the barriers to genetic engineering would directly help in increasing genome-editing rates. Thus, this review aims to compare various legumes for their transformation, editing, and regeneration efficiencies and discusses various solutions available for increasing transformation and genome-editing rates in legumes.

Gene-Editing Technologies and Applications in Legumes: Progress, Evolution, and Future Prospects

Legumes are rich in protein and phytochemicals and have provided a healthy diet for human beings for thousands of years. In recognition of the important role they play in human nutrition and agricultural production, the researchers have made great efforts to gain new genetic traits in legumes such as yield, stress tolerance, and nutritional quality. In recent years, the significant increase in genomic resources for legume plants has prepared the groundwork for applying cutting-edge breeding technologies, such as transgenic technologies, genome editing, and genomic selection for crop improvement. In addition to the different genome editing technologies including the CRISPR/Cas9-based genome editing system, this review article discusses the recent advances in plant-specific gene-editing methods, as well as problems and potential benefits associated with the improvement of legume crops with important agronomic properties. The genome editing technologies have been effectively used in different legume plants including model legumes like alfalfa and lotus, as well as crops like soybean, cowpea, and chickpea. We also discussed gene-editing methods used in legumes and the improvements of agronomic traits in model and recalcitrant legumes. Despite the immense opportunities genome editing can offer to the breeding of legumes, governmental regulatory restrictions present a major concern. In this context, the comparison of the regulatory framework of genome editing strategies in the European Union and the United States of America was also discussed. Gene-editing technologies have opened up new possibilities for the improvement of significant agronomic traits in legume breeding.

Management of stored grain pest with special reference to Callosobruchus maculatus, a major pest of cowpea: A review

Bruchids are most pernicious pest of stored grain pulses, especially in the tropical and subtropical areas. They penetrate into the fully grown matured pods, grains in fields and also during post-harvest storage. Among bruchids, Callosobruchus maculatus is the prominent pest having ubiquitous distribution. Chemical/synthetic insecticides provides adequate control against the C. maculatus on the pulses. However, the use of synthetic insecticides induces adverse health outcomes in agricultural workers and many causes various diseases such as cancers, genomic damage, oxidative stress, neurological disorders and respiratory, metabolic and thyroid effects. Therefore, alternative effective, safe and sustainable pest control, integration of different compatible methods should be taken into considerations. One of the possible managements might be use of traditional as well modern pest management practices. Traditional techniques include sealed containers, inert materials, harvesting time, alternate host, intercropping, storing un-threshed pulses, cleanliness, vegetable oil etc. Modern techniques such as temperature, freezing and heating, radiation treatments, resistance varieties, natural control, botanical extracts, chemical and microbial, transgenic approach, cold plasma treatments etc. thus integrated pest management might be alternative approach to combat the effect of pest. Therefore, present review aims to considers various measures for the handling of bruchids with special reference to Callosobruchus maculatus and integrated molecular inventions to decrease bruchids populations and enhance pulse productivity in pulses.

Genetic transformation of legumes: an update

This review summarizes the recent advances in legume genetic transformation and provides an insight into the critical factors that play a major role in the process. It also sheds light on some of the potential areas which may ameliorate the transformation of legumes. Legumes are an important group of dicotyledonous plants, highly enriched in proteins and minerals. Majority of the legume plants are cultivated in the arid and semi-arid parts of the world, and hence said to be climate resilient. They have the capability of atmospheric nitrogen fixation and thus play a vital role in the ecological sphere. However, the worldwide production of legumes is somehow not up to the mark and the yields are greatly affected by various biotic and abiotic stress factors. Genetic engineering strategies have emerged as a core of plant biology and remarkably facilitate the crop improvement programmes. A significant progress has been made towards the optimization of efficient transformation system for legume plants over the years but this group is still underutilized in comparison to other crops. Among the variety of available DNA delivery systems, Agrobacterium-mediated and particle bombardment have been primarily deployed for optimization and trait improvement. However, recalcitrance and genotype-dependence are some of the major bottlenecks for successful transformation. In this context, the present review summarizes the advances taken place in the area of legume transformation and provides an insight into the present scenario. The challenges and future possibilities for yield improvement have also been discussed.

Robust Genetic Transformation System to Obtain Non-chimeric Transgenic Chickpea

Chickpea transformation is an important component for the genetic improvement of this crop, achieved through modern biotechnological approaches. However, recalcitrant tissue cultures and occasional chimerism, encountered during transformation, hinder the efficient generation of transgenic chickpeas. Two key parameters, namely micro-injury and light emitting diode (LED)-based lighting were used to increase transformation efficiency. Early PCR confirmation of positive in vitro transgenic shoots, together with efficient grafting and an extended acclimatization procedure contributed to the rapid generation of transgenic plants. High intensity LED light facilitate chickpea plants to complete their life cycle within 9 weeks thus enabling up to two generations of stable transgenic chickpea lines within 8 months. The method was validated with several genes from different sources, either as single or multi-gene cassettes. Stable transgenic chickpea lines containing GUS (uidA), stress tolerance (AtBAG4 and TlBAG), as well as Fe-biofortification (OsNAS2 and CaNAS2) genes have successfully been produced.

Robust Genetic Transformation System to Obtain Non-chimeric Transgenic Chickpea

Chickpea transformation is an important component for the genetic improvement of this crop, achieved through modern biotechnological approaches. However, recalcitrant tissue cultures and occasional chimerism, encountered during transformation, hinder the efficient generation of transgenic chickpeas. Two key parameters, namely micro-injury and light emitting diode (LED)-based lighting were used to increase transformation efficiency. Early PCR confirmation of positive in vitro transgenic shoots, together with efficient grafting and an extended acclimatization procedure contributed to the rapid generation of transgenic plants. High intensity LED light facilitate chickpea plants to complete their life cycle within 9 weeks thus enabling up to two generations of stable transgenic chickpea lines within 8 months. The method was validated with several genes from different sources, either as single or multi-gene cassettes. Stable transgenic chickpea lines containing GUS (uidA), stress tolerance (AtBAG4 and TlBAG), as well as Fe-biofortification (OsNAS2 and CaNAS2) genes have successfully been produced.

Elite hairy roots of Raphanus sativus (L.) as a source of antioxidants and flavonoids

An efficient protocol for hairy root induction in radish was established by optimizing several parameters that affect the efficiency of Agrobacterium rhizogenes-mediated transformations. Explants wounded using sterile hypodermic needle, infected with Agrobacterium suspension (0.6 OD600) for 10 min and co-cultivated in 1/2 MS medium containing acetosyringone (100 µM) for 2 days displayed maximum percentage of hairy root induction using MTCC 2364 (77.6%) and MTCC 532 (67.6%). On further experiments with MTCC 2364 initiated hairy roots, maximum biomass accumulation (fresh weight = 9.50 g; dry weight = 1.48 g) was achieved in liquid 1/2 MS medium supplemented with 87.6 mM sucrose after 40 days of culture. Transgenic state of hairy roots of MTCC 2364 was confirmed by polymerase chain reaction using rolB- and rolC-specific primers. The MTCC 2364-induced hairy roots produced higher amount of phenolic (33.0 mg g-1), flavonoid (48.0 mg g-1), and quercetin (114.8 mg g-1) content compared to auxin-induced roots of non-transformed radish. Furthermore, the results of ferric reducing antioxidant power and 1,1-diphenyl-2-picrylhydrazyl assay confirmed that the antioxidant activity of MTCC 2364 root extracts was improved when compared to auxin-induced roots of non-transformed radish. The present study offers a new insight in radish for production of phenolics and flavonoids (quercetin) using A. rhizogenes-mediated hairy root induction.

Co-expression of Arabidopsis NHX1 and bar Improves the Tolerance to Salinity, Oxidative Stress, and Herbicide in Transgenic Mungbean

Mungbean is an important pulse crop extensively cultivated in Southeast Asia for supply of easily digestible protein. Salinity severely limits the growth and productivity of mungbean, and weeding poses nutritional and disease constraints to mungbean cultivation. To pyramid both salt tolerance and protection against herbicide in mungbean, the AtNHX1 encoding tonoplast Na+/H+ antiporter from Arabidopsis, and bar gene associated with herbicide resistance were co-expressed through Agrobacterium-mediated transformation. Stress inducible expression of AtNHX1 significantly improved tolerance under salt stress to ionic, osmotic, and oxidative stresses in transgenic mungbean plants compared to the wild type (WT) plants, whereas constitutive expression of bar provided resistance to herbicide. Compared to WT, transgenic mungbean plants grew better with higher plant height, foliage, dry mass and seed yield under high salt stress (200 mM NaCl) in the greenhouse. The improved performance of transgenic plants under salt stress was associated with enhanced sequestration of Na+ in roots by vacuolar Na+/H+ antiporter and limited transport of toxic Na+ to shoots, possibly by restricting Na+ influx into shoots. Transgenic plants showed better intracellular ion homeostasis, osmoregulation, reduced cell membrane damage, improved photosynthetic capacity, and transpiration rate as compared to WT when subjected to salt stress. Reduction in hydrogen peroxide and oxygen radical production indicated enhanced protection of transgenic plants to both salt- and methyl vialogen (MV)-induced oxidative stress. This study laid a firm foundation for improving mungbean yield in saline lands in Southeast Asia.

Ex vitro hairy root induction in detached peanut leaves for plant-nematode interaction studies

BACKGROUND

Peanut (Arachis hypogaea) production is largely affected by a variety of abiotic and biotic stresses, including the root-knot nematode (RKN) Meloidogyne arenaria that causes yield losses worldwide. Transcriptome studies of wild Arachis species, which harbor resistance to a number of pests and diseases, disclosed several candidate genes for M. arenaria resistance. Peanut is recalcitrant to genetic transformation, so the use of Agrobacterium rhizogenes-derived hairy roots emerged as an alternative for in-root functional characterization of these candidate genes.

RESULTS

The present report describes an ex vitro methodology for hairy root induction in detached leaves based on the well-known ability of peanut to produce roots spontaneously from its petiole, which can be maintained for extended periods under high-humidity conditions. Thirty days after infection with the A. rhizogenes 'K599' strain, 90% of the detached leaves developed transgenic hairy roots with 5 cm of length in average, which were then inoculated with M. arenaria. For improved results, plant transformation, and nematode inoculation parameters were adjusted, such as bacterial cell density and growth stage; moist chamber conditions and nematode inoculum concentration. Using this methodology, a candidate gene for nematode resistance, AdEXLB8, was successfully overexpressed in hairy roots of the nematode-susceptible peanut cultivar 'Runner', resulting in 98% reduction in the number of galls and egg masses compared to the control, 60 days after M. arenaria infection.

CONCLUSIONS

This methodology proved to be more practical and cost-effective for functional validation of peanut candidate genes than in vitro and composite plant approaches, as it requires less space, reduces analysis costs and displays high transformation efficiency. The reduction in the number of RKN galls and egg masses in peanut hairy roots overexpressing AdEXLB8 corroborated the use of this strategy for functional characterization of root expressing candidate genes. This approach could be applicable not only for peanut-nematode interaction studies but also to other peanut root diseases, such as those caused by fungi and bacteria, being also potentially extended to other crop species displaying similar petiole-rooting competence.

Development of an efficient in vitro plant regeneration system amenable to Agrobacterium- mediated transformation of a recalcitrant grain legume blackgram (Vigna mungo L. Hepper)

An efficient, rapid and direct multiple shoot regeneration system amenable to Agrobacterium-mediated transformation from primary leaf with intact petiole of blackgram (Vigna mungo) is established for the first time. The effect of the explant type and its age, type and concentration of cytokinin and auxin either alone or in combination and genotype on multiple shoot regeneration efficiency and frequency was optimized. The primary leaf explants with petiole excised from 4-day-old seedlings directly developed multiple shoots (an average of 10 shoots/ explant) from the cut ends of the petiole in 95 % of the cultures on MSB (MS salts and B5 vitamins) medium containing 1.0 μM 6-benzylaminopurine. Elongated (2-3 cm) shoots were rooted on MSB medium with 2.5 μM indole-butyric acid and resulted plantlets were hardened and established in soil, where they resumed growth and reached maturity with normal seed set. The regenerated plants were morphologically similar to seed-raised plants and required 8 weeks time from initiation of culture to establish them in soil. The regeneration competent cells present at the cut ends of petiole are fully exposed and are, thus, easily accessible to Agrobacterium, making this plant regeneration protocol amenable for the production of transgenic plants. The protocol was further successfully used to develop fertile transgenic plants of blackgram using Agrobacterium tumefaciens strain EHA 105 carrying a binary vector pCAMBIA2301 that contains a neomycin phosphotransferase gene (nptII) and a β-glucuronidase (GUS) gene (uidA) interrupted with an intron. The presence and integration of transgenes in putative T0 plants were confirmed by polymerase chain reaction (PCR) and Southern blot hybridization, respectively. The transgenes were inherited in Mendelian fashion in T1 progeny and a transformation frequency of 1.3 % was obtained. This protocol can be effectively used for transferring new traits in blackgram and other legumes for their quantitative and qualitative improvements.

High-throughput transformation pipeline for a Brazilian japonica rice with bar gene selection

The goal of this work was to establish a transformation pipeline for upland Curinga rice (Oryza sativa L. ssp. japonica) with bar gene selection employing bialaphos and phosphinothricin as selection agents. The following genes of interest: AtNCED3, Lsi1, GLU2, LEW2, PLD-alpha, DA1, TOR, AVP1, and Rubisco were cloned into the binary vector p7i2x-Ubi and were transferred into Agrobacterium strain EHA 105. Embryogenic calli derived from the mature embryos were transformed, and transgenic cells and shoots were selected on the medium supplemented with bialaphos or phosphinothricin (PPT) using a stepwise selection scheme. Molecular analyses were established using polymerase chain reaction and Southern blot for the bar gene and the NOS terminator. Overall, 273 putative transgenic plants were analyzed by Southern blot with 134 events identified. In total, 77 events had a single copy of the transgene integrated in the plant genome while 29 events had two copies. We tested backbone integration in 101 transgenic plants from all constructs and found 60 transgenic plants having no additional sequence integrated in the plant genome. The bar gene activity was evaluated by the chlorophenol red test and the leaf painting test using phosphinothricin with several transgenic plants. The majority of T0 plants carrying the single copy of transgene produced T1 seeds in the screen house.

Sonication, Vacuum Infiltration and Thiol Compounds Enhance the Agrobacterium-Mediated Transformation Frequency of Withania somnifera (L.) Dunal

In the present study, we have established a stable transformation protocol via Agrobacterium tumafacines for the pharmaceutically important Withania somnifera. Six day-old nodal explants were used for 3 day co-cultivation with Agrobacterium tumefaciens strain LBA4404 harbouring the vector pCAMIBA2301. Among the different injury treatments, sonication, vacuum infiltration and their combination treatments tested, a vacuum infiltration for 10 min followed by sonication for 10 sec with A. tumefaciens led to a higher transient GUS expression (84% explants expressing GUS at regenerating sites). In order to improve gene integration, thiol compounds were added to co-cultivation medium. A combined treatment of L-Cys at 100 mg/l, STS at 125 mg/l, DTT at 75 mg/l resulted in a higher GUS expression (90%) in the nodal explants. After 3 days of co-cultivation, the explants were subjected to three selection cycles with increasing concentrations of kanamycin [100 to 115 mg/l]. The integration and expression of gusA gene in T0 and T1 transgenic plants were confirmed by polymerase chain reaction (PCR), and Southern blott analysis. These transformed plants (T0 and T1) were fertile and morphologically normal. From the present investigation, we have achieved a higher transformation efficiency of (10%). Withanolides (withanolide A, withanolide B, withanone and withaferin A) contents of transformed plants (T0 and T1) were marginally higher than control plants.

Enhanced antifungal and insect α-amylase inhibitory activities of Alpha-TvD1, a peptide variant of Tephrosia villosa defensin (TvD1) generated through in vitro mutagenesis

TvD1 is a small, cationic, and highly stable defensin from the weedy legume, Tephrosia villosa with demonstrated in vitro antifungal activity. We show here peptide modifications in TvD1 that lead to enhanced antifungal activities. Three peptide variants, S32R, D37R, and Alpha-TvD1 (-G-M-T-R-T-) with variations in and around the β2-β3 loop region that imposes the two β-strands, β2 and β3 were generated through in vitro mutagenesis. Alpha-TvD1 exhibited enhanced antifungal activity against the fungal pathogens, Fusarium culmorum and Fusarium oxysporum with respective IC(50) values of 2.5 μM and 3.0 μM, when compared to S32R (<5.0 μM and >5.0 μM), D37R (5.5 μM and 4.5 μM), and the wild type TvD1 (6.5 μM). Because of the enhanced antifungal activity, this variant peptide was characterized further. Growth of F. culmorum in the presence of Alpha-TvD1 showed deformities in hyphal walls and nuclear damage. With respect to the plant pathogenic bacterium, Pseudomonas syringae pv. tomato strain DC3000, both Alpha-TvD1 and the wild type TvD1 showed comparable antibacterial activity. Both wild type TvD1 and Alpha-TvD1 displayed inhibitory activity against the α-amylase of the mealworm beetle, Tenebrio molitor (TMA) with the latter showing enhanced activity. The human salivary as well as barley α-amylase activities were not inhibited even at concentrations of up to 50 μM, which has been predicted to be due to differences in the pocket size and the size of the interacting loops. Present study shows that the variant Alpha-TvD1 exhibits enhanced antifungal as well as insect α-amylase inhibitory activity.

Mungbean plants expressing BjNPR1 exhibit enhanced resistance against the seedling rot pathogen, Rhizoctonia solani

Mungbean, Vigna radiata (L.) Wilczek is an important pulse crop that is widely cultivated in semi- arid tropics. The crop is attacked by various soil-borne pathogens like Rhizoctonia solani, which causes dry rot disease and seriously affects its productivity. Earlier we characterized the non-expressor of pathogenesis related gene-1(BjNPR1) of mustard, Brassica juncea, the counterpart of AtNPR1 of Arabidopsis thaliana. Here, we transformed mungbean with BjNPR1 via Agrobacterium tumefaciens. Because of the recalcitrant nature of mungbean, the effect of some factors like Agrobacterium tumefaciens strains (GV2260 and LBA4404), pH, L: -cysteine and tobacco leaf extract was tested in transformation. The transgenic status of 15 plants was confirmed by PCR using primers for nptII. The independent integration of T-DNA in transgenic plants was analyzed by Southern hybridization with an nptII probe and the expression of BjNPR1 was confirmed by RT-PCR. Some of the T(0) plants were selected for detached leaf anti-fungal bioassay using the fungus Rhizoctonia solani, which showed moderate to high level of resistance depending on the level of expression of BjNPR1. The seedling bioassay of transgenic T(2) plants indicated resistance against dry rot disease caused by R. solani.

Transgenic ramie [Boehmeria nivea (L.) Gaud.]: factors affecting the efficiency of Agrobacterium tumefaciens-mediated transformation and regeneration

In the present study, an efficient Agrobacterium-mediated gene transformation system was developed for ramie [Boehmeria nivea (L.) Gaud.] based on the examinations of several factors affecting plant transformation efficiency. The effects of Agrobacterium cell density, acetosyringone, co-cultivation temperature, co-cultivation duration, co-cultivation photoperiod and pH on stable transformation were evaluated. Agrobacterium at a concentration of OD = 0.5-0.8 improved the efficiency of transformation. Concentration of acetosyringone at 50 mg/L during co-cultivation significantly increased transformation efficiency. Co-cultivation at 20 degrees C, in comparison to 15, 25 and 28 degrees C, consistently resulted in higher transformation frequencies. A relatively short co-cultivation duration (3 days) was optimal for ramie transformation. Co-cultivation medium at pH 5.9 and co-cultivation in darkness both improved the transformation efficiencies of ramie. An overall scheme for producing transgenic ramie is presented, through which an average transformation rate from 10.5 to 24.7% in five ramie varieties was obtained. Stable expression and integration of the transgenes were confirmed by histochemical GUS assay, kanamycin painting assay, PCR and Southern blotting. This optimized transformation system should be employed for efficient Agrobacterium-mediated transformation of ramie.

Agrobacterium tumefaciens-mediated genetic transformation of a recalcitrant grain legume, lentil (Lens culinaris Medik)

A simple and reproducible Agrobacterium-mediated transformation protocol for a recalcitrant legume plant, lentil (Lens culinaris M.) is reported. Application of wounding treatments and efficiencies of three Agrobacterium tumefaciens strains, EHA105, C58C1, and KYRT1 were compared for T-DNA delivery into lentil cotyledonary node tissues. KYRT1 was found to be on average 2.8-fold more efficient than both EHA105 and C58C1 for producing transient beta-glucuronidase (GUS) gene (gus) expression on cotyledonary petioles. Wounding of the explants, use of an optimized transformation protocol with the application of acetosyringone and vacuum infiltration treatments in addition to the application of a gradually intensifying selection regime played significant roles in enhancing transformation frequency. Lentil explants were transformed by inoculation with Agrobacterium tumefaciens strain, KYRT1 harboring a binary vector pTJK136 that carried neomycin phosphotransferase gene (npt-II) and an intron containing gusA gene on its T-DNA region. GUS-positive shoots were micrografted on lentil rootstocks. Transgenic lentil plants were produced with an overall transformation frequency of 2.3%. The presence of the transgene in the lentil genome was confirmed by GUS assay, PCR, RT-PCR and Southern hybridization. The transgenic shoots grafted on rootstocks were successfully transferred to soil and grown to maturity in the greenhouse. GUS activity was detected in vegetative and reproductive organs of T(0), T(1), T(2) and T(3) plants. PCR assays of T(1), T(2) and T(3) progenies confirmed the stable transmission of the transgene to the next generations.

Genetic transformation and regeneration of Sesbania drummondii using cotyledonary nodes

Sesbania drummondii (Rydb.) Cory is a source for phytopharmaceuticals. It also hyperaccumulates several toxic heavy metals. Development of an efficient gene transfer method is an absolute requirement for the genetic improvement of this plant with more desirable traits due to limitations in conventional breeding methods. A simple protocol was developed for Agrobacterium-mediated stable genetic transformation of Sesbania. Agrobacterium tumefaciens strain EHA 101 containing the vector pCAMBIA 1305.1 having hptII and GUS plus genes was used for the gene transfer experiments. Evaluation of various parameters was carried out to assess the transformation frequency by GUS expression analysis. High transformation frequency was achieved by using 7-day-old precultured cotyledonary node (CN) explants. Further, the presence of acetosyringone (150 muM), infection of explants for 30-45 min and 3 days of cocultivation proved to be critical factors for greatly improving the transformation efficiency. Stable transformation of S. drummondii was achieved, and putative transgenic shoots were obtained on medium supplemented with hygromycin (25 mg l(-1)). GUS histochemical analysis of the putative transgenic tissues further confirmed the transformation event. Genomic Southern blot analysis was performed to verify the presence of transgenes and their stable integration. A transformation frequency of 4% was achieved for CN explants using this protocol.

Novel insights on the mechanism of action of alpha-amylase inhibitors from the plant defensin family

Plant defensins are small cysteine-rich proteins commonly synthesized in plants, encoded by large multigene families. Most plant defensins that have been characterized to date show potent antifungal and/or bactericidal activities. This report describes VuD1, an unusual defensin that is able to inhibit insect-pest alpha-amylases. VuD1 was cloned from cowpea (Vigna unguiculata) seeds and expressed in a heterologous system. Inhibitory enzyme assays showed that VuD1 efficiently inhibits alpha-amylases from the weevils Acanthoscelides obtectus and Zabrotes subfasciatus, caused low inhibition toward mammalian enzymes and was unable to inhibit the alpha-amylases from Callosobruchus maculatus and Aspergillus fumigatus. To shed some light over the mechanism of action of VuD1, molecular modeling analyses were performed, revealing that the N-terminus of the molecule is responsible for binding with the active site of weevil enzymes. Moreover, models of VuD1 and mammalian enzymes were also generated to elucidate the specificity mechanisms. The data presented herein suggests that this defensin has potential application in the development of transgenic plants for insect pest control.

Advances in development of transgenic pulse crops

It is three decades since the first transgenic pulse crop has been developed. Todate, genetic transformation has been reported in all the major pulse crops like Vigna species, Cicer arietinum, Cajanus cajan, Phaseolus spp, Lupinus spp, Vicia spp and Pisum sativum, but transgenic pulse crops have not yet been commercially released. Despite the crucial role played by pulse crops in tropical agriculture, transgenic pulse crops have not moved out from laboratories to large farm lands compared to their counterparts - 'cereals' and the closely related leguminous oil crop - 'soybean'. The reason for lack of commercialization of transgenic pulse crops can be attributed to the difficulty in developing transgenics with reproducibility, which in turn is due to lack of competent totipotent cells for transformation, long periods required for developing transgenics and lack of coordinated research efforts by the scientific community and long term funding. With optimization of various factors which influence genetic transformation of pulse crops, it will be possible to develop transgenic plants in this important group of crop species with more precision and reproducibility. A translation of knowledge from information available in genomics and functional genomics in model legumes like Medicago truncatula and Lotus japonicus relating to factors which contribute to enhancing crop yield and ameliorate the negative consequences of biotic and abiotic stress factors may provide novel insights for genetic manipulation to improve the productivity of pulse crops.