Use of a herbicide or lysine plus threonine for non-antibiotic selection of transgenic chickpea

Exploring Chickpea Germplasm Diversity for Broadening the Genetic Base Utilizing Genomic Resourses

Legume crops provide significant nutrition to humans as a source of protein, omega-3 fatty acids as well as specific macro and micronutrients. Additionally, legumes improve the cropping environment by replenishing the soil nitrogen content. Chickpeas are the second most significant staple legume food crop worldwide behind dry bean which contains 17%–24% protein, 41%–51% carbohydrate, and other important essential minerals, vitamins, dietary fiber, folate, β-carotene, anti-oxidants, micronutrients (phosphorus, calcium, magnesium, iron, and zinc) as well as linoleic and oleic unsaturated fatty acids. Despite these advantages, legumes are far behind cereals in terms of genetic improvement mainly due to far less effort, the bottlenecks of the narrow genetic base, and several biotic and abiotic factors in the scenario of changing climatic conditions. Measures are now called for beyond conventional breeding practices to strategically broadening of narrow genetic base utilizing chickpea wild relatives and improvement of cultivars through advanced breeding approaches with a focus on high yield productivity, biotic and abiotic stresses including climate resilience, and enhanced nutritional values. Desirable donors having such multiple traits have been identified using core and mini core collections from the cultivated gene pool and wild relatives of Chickpea. Several methods have been developed to address cross-species fertilization obstacles and to aid in inter-specific hybridization and introgression of the target gene sequences from wild Cicer species. Additionally, recent advances in “Omics” sciences along with high-throughput and precise phenotyping tools have made it easier to identify genes that regulate traits of interest. Next-generation sequencing technologies, whole-genome sequencing, transcriptomics, and differential genes expression profiling along with a plethora of novel techniques like single nucleotide polymorphism exploiting high-density genotyping by sequencing assays, simple sequence repeat markers, diversity array technology platform, and whole-genome re-sequencing technique led to the identification and development of QTLs and high-density trait mapping of the global chickpea germplasm. These altogether have helped in broadening the narrow genetic base of chickpeas.

K. S, Thakur S, Rathore M, Verma OP, Singh NP, Das A. Evaluation of transgenic chickpea harboring codon-modified Vip3Aa against gram pod borer (Helicoverpa armigera H.)

The gram pod borer is a major pest of chickpea, accounting for average annual yield losses to the tune of 40-50%. VIP3Aa, a class of insecticidal protein with different receptor binding site in the insect's midgut compared to Bt-crystal protein, offers an alternative protection strategy against Lepidopteran insects. Here, we report evaluation of genetically engineered chickpea lines harboring codon modified Vip3Aa (cmVip3Aa) against the Lepidopteran insect pest, gram pod borer. The synthetic codon modified, cmVip3Aa gene of 2,370 bp was sub-cloned in modified plant expression vector and used for direct transformation of embryonic axis explants of chickpea (cv. DCP 92-3), with transformation efficiency of 4.30%. Presence and transmission of transgene across two generations were confirmed by PCR and Southern blot analyses in the five selected transgenic chickpea lines. Real Time PCR analyses indicated variable levels of cmVip3Aa expression in the transgenic chickpea lines (average Cq values 15.01±0.86 to 19.32±0.10), which were absent in the non-transgenic counterpart. Detached leaf insect bioassay indicate larval mortality (up to 39.75%), reduced larval feeding (up to 82.91%) and reduced larval weight gain (up to 68.23%), compared to control lines. Evaluation of gene offers a platform to identify efficacious insecticidal gene that can be used for insect resistance management in chickpea.

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.

Viruses and Phytoparasitic Nematodes of Cicer arietinum L.: Biotechnological Approaches in Interaction Studies and for Sustainable Control

Cicer arietinum L. (chickpea) is the world's fourth most widely grown pulse. Chickpea seeds are a primary source of dietary protein for humans, and chickpea cultivation contributes to biological nitrogen fixation in the soil, given its symbiotic relationship with rhizobia. Therefore, chickpea cultivation plays a pivotal role in innovative sustainable models of agro-ecosystems inserted in crop rotation in arid and semi-arid environments for soil improvement and the reduction of chemical inputs. Indeed, the arid and semi-arid tropical zones of Africa and Asia have been primary areas of cultivation and diversification. Yet, nowadays, chickpea is gaining prominence in Canada, Australia, and South America where it constitutes a main ingredient in vegetarian and vegan diets. Viruses and plant parasitic nematodes (PPNs) have been considered to be of minor and local impact in primary areas of cultivation. However, the introduction of chickpea in new environments exposes the crop to these biotic stresses, compromising its yields. The adoption of high-throughput genomic technologies, including genome and transcriptome sequencing projects by the chickpea research community, has provided major insights into genome evolution as well as genomic architecture and domestication. This review summarizes the major viruses and PPNs that affect chickpea cultivation worldwide. We also present an overview of the current state of chickpea genomics. Accordingly, we explore the opportunities that genomics, post-genomics and novel editing biotechnologies are offering in order to understand chickpea diseases and stress tolerance and to design innovative control strategies.

High-efficiency Agrobacterium-mediated transformation of chickpea (Cicer arietinum L.) and regeneration of insect-resistant transgenic plants

To develop an efficient genetic transformation system of chickpea (Cicer arietinum L.), callus derived from mature embryonic axes of variety P-362 was transformed with Agrobacterium tumefaciens strain LBA4404 harboring p35SGUS-INT plasmid containing the uidA gene encoding β-glucuronidase (GUS) and the nptII gene for kanamycin selection. Various factors affecting transformation efficiency were optimized; as Agrobacterium suspension at OD(600) 0.3 with 48 h of co-cultivation period at 20°C was found optimal for transforming 10-day-old MEA-derived callus. Inclusion of 200 μM acetosyringone, sonication for 4 s with vacuum infiltration for 6 min improved the number of GUS foci per responding explant from 1.0 to 38.6, as determined by histochemical GUS assay. For introducing the insect-resistant trait into chickpea, binary vector pRD400-cry1Ac was also transformed under optimized conditions and 18 T(0) transgenic plants were generated, representing 3.6% transformation frequency. T(0) transgenic plants reflected Mendelian inheritance pattern of transgene segregation in T(1) progeny. PCR, RT-PCR, and Southern hybridization analysis of T(0) and T(1) transgenic plants confirmed stable integration of transgenes into the chickpea genome. The expression level of Bt-Cry protein in T(0) and T(1) transgenic chickpea plants was achieved maximum up to 116 ng mg(-1) of soluble protein, which efficiently causes 100% mortality to second instar larvae of Helicoverpa armigera as analyzed by an insect mortality bioassay. Our results demonstrate an efficient and rapid transformation system of chickpea for producing non-chimeric transgenic plants with high frequency. These findings will certainly accelerate the development of chickpea plants with novel traits.

Agrobacterium-mediated transformation in chickpea (Cicer arietinum L.) with an insecticidal protein gene: optimisation of different factors

Agrobacterium-mediated transformation in chickpea was developed using strain LBA4404 carrying nptII, uidA and cryIAc genes and transformants selected on Murashige and Skoog's basal medium supplemented with benzyladenine, kinetin and kanamycin. Integration of transgenes was demonstrated using polymerase chain reaction and Southern blot hybridization of T0 plants. The expression of CryIAc delta endotoxin and GUS enzyme was shown by enzyme linked immunosorbent assay and histochemical assay respectively. The transgenic plants (T0) showed more tolerance to infection by Helicoverpa armigera compared to control plants. Various factors such as explant source, cultivar type, different preculture treatment period of explants, co-cultivation period, acetosyringone supplementation, Agrobacterium harboring different plasmids, vacuum infiltration and sonication treatment were tested to study the influence on transformation frequency. The results indicated that use of epicotyl as explant, cultivar ICCC37, Agrobacterium harboring plasmid pHS102 as vector, preculture of explant for 48 h, co-cultivation period of 2 days at 25°C and vacuum infiltration for 15 min produced the best transformation results. Sonication treatment of explants with Agrobacteria for 80 s was found to increase the frequency of transformation.

Development of a phosphomannose isomerase-based Agrobacterium-mediated transformation system for chickpea (Cicer arietinum L.)

To develop an alternative genetic transformation system that is not dependent on an antibiotic selection strategy, the phosphomannose isomerase gene (pmi) system was evaluated for producing transgenic plants of chickpea (Cicer arietinum L.). A shoot morphogenesis protocol based on the thidiazuron (TDZ)-induced shoot morphogenesis system was combined with Agrobacterium-mediated transformation of the pmi gene and selection of transgenic plants on mannose. Embryo axis explants of chickpea cv. C-235 were grown on a TDZ-supplemented medium for shoot proliferation. Embryo axis explants from which the first and second flush of shoots were removed were transformed using Agrobacterium carrying the pmi gene, and emerging shoots were allowed to regenerate on a zeatin-supplemented medium with an initial selection pressure of 20 g l(-1) mannose. Rooting was induced in the selected shoots on an indole-3-butyric acid (IBA)-supplemented medium with a selection pressure of 15 g l(-1) mannose. PCR with marker gene-specific primers and chlorophenol red (CPR) assay of the shoots indicated that shoots had been transformed. RT-PCR and Southern analysis of selected regenerated plants further confirmed integration of the transgene into the chickpea genome. These positive results suggest that the pmi/mannose selection system can be used to produce transgenic plants of chickpea that are free from antibiotic resistance marker genes.

An optimal protocol for in vitro regeneration, efficient rooting and stable transplantation of chickpea

A rapid, reproducible and efficient regeneration method was developed for chickpea (Cicer arietinum L.) using single cotyledon with half embryonal axis as explants. MS medium supplemented with 4 ìM TDZ, 10 ìM 2-iP and 2 ìM kinetin induced 50-100 adventitious buds/shoots after 14 days of culture and elongated on MS medium supplemented with 5 ìM 2-iP and 2 ìM kinetin. Healthy, strong and 100 % rooting was achieved by exposing cut ends of the shoots to 10 sec pulse treatment with 100 ìmoles/ml IBA followed by their transfer to liquid MS basal medium within 10-14 d. 2-3 cm long shoots were most suitable for rooting. Potting-mixture with good aeration and lesser capacity to retain water was most suitable for achieving successful establishment of chickpea plantlets. Garden soil mixed with sand (gravel) and bio-manure in the ratio of 1:1:1 is most suitable for achieving cent percent transplantation success. Cent percent of plantlets got acclimatized, survived in the pots and showed normal growth, development, flowering followed by podding and seeds setting. Harvesting of seeds was done after the pods were fully matured and dry. In this communication, we have demonstrated for the first time that shoot length, pulse treatment of cut ends of shoots with 100 ìmoles/ml IBA and aeration of potting mixture are key factors for rapid micro-propagation and successful establishment of chickpea.

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.

Genetic transformation of chickpea (Cicer arietinum L.) with insecticidal crystal protein gene using particle gun bombardment

Here, we report the establishment of an efficient particle gun bombardment mediated genetic transformation in chickpea (Cicer arietinum L.) using cryIAc gene of Bacillus thuringiensis. Explants were bombarded with recombinant plasmids engineered for the expression of cryIAc transgene in plants and stable transformants regenerated in presence of benzyladenine, kinetin and kanamycin. Transformation frequency showed dependence on explant type, cultivars, plasmids, helium pressure and microcarrier type used. Integration of transgenes was demonstrated using polymerase chain reaction and Southern blot hybridization approaches in T (0) plants. The expression of CryIA(c) delta-endotoxin and GUS enzyme was ascertained by enzyme linked immunosorbent assay and histochemical assays, respectively. These transgenic plants (T (0)) showed more protection and high mortality for Heliothis armigera and Spodoptera litura larvae as compared to control plants. The results of the present study indicate that highest transformation frequency (18%) could be achieved by use of gold as a microcarrier in combination with helium pressure of 900 psi. Among the other factors tested, plasmid pHS 102 was the most efficient plasmid, while epicotyl explant was the best explant source for particle gun bombardment. Among the different cultivars of chickpea tested, cultivar ICCC37 and PG-12 produced higher frequency of transformation frequency compared to others.

Agrobacterium-mediated transformation of chickpea with alpha-amylase inhibitor gene for insect resistance

Chickpea is the world's third most important pulse crop and India produces 75% of the world's supply. Chickpea seeds are attacked by Callosobruchus maculatus and C. chinensis which cause extensive damage. The alpha-amylase inhibitor gene isolated from Phaseolus vulgaris seeds was introduced into chickpea cultivar K850 through Agrobacterium-mediated transformation. A total of 288 kanamycin resistant plants were regenerated. Only 0.3% of these were true transformants. Polymerase chain reaction (PCR) analysis and Southern hybridization confirmed the presence of 4.9 kb alpha-amylase inhibitor gene in the transformed plants. Western blot confirmed the presence of alpha-amylase inhibitor protein. The results of bioassay study revealed a significant reduction in the survival rate of bruchid weevil C. maculatus reared on transgenic chickpea seeds. All the transgenic plants exhibited a segregation ratio of 3:1.

The aspartic acid metabolic pathway, an exciting and essential pathway in plants

Aspartate is the common precursor of the essential amino acids lysine, threonine, methionine and isoleucine in higher plants. In addition, aspartate may also be converted to asparagine, in a potentially competing reaction. The latest information on the properties of the enzymes involved in the pathways and the genes that encode them is described. An understanding of the overall regulatory control of the flux through the pathways is undisputedly of great interest, since the nutritive value of all cereal and legume crops is reduced due to low concentrations of at least one of the aspartate-derived amino acids. We have reviewed the recent literature and discussed in this paper possible methods by which the concentrations of the limiting amino acids may be increased in the seeds.

An efficient transformation system for chickpea (Cicer arietinum L.)

A reproducible and efficient transformation method was developed for Desi and Kabuli chickpeas (Cicer arietinum L.) using germinated seedlings as sources of explants. Slices derived from plumules were the most efficient at generating transformed shoots. The AGL1 Agrobacterium-treated explants were first incubated on thidiazuron-containing media, then selected using phosphinothricin. Resistant shoots were successfully transferred to soil either by grafting or in vitro rooting. In experiments each taking 4-9 months, a total of 41 confirmed transformed lines were created using embryo axis slices as source explants, giving a transformation frequency of 5.1%. Southern analysis and histochemical and leaf painting assays demonstrated integration and expression of the transgenes in the initial transformants and two generations of progeny.