Recovery of transgenic plants by pollen-mediated transformation in Brassica juncea

A comprehensive review of in planta stable transformation strategies

Plant transformation remains a major bottleneck to the improvement of plant science, both on fundamental and practical levels. The recalcitrant nature of most commercial and minor crops to genetic transformation slows scientific progress for a large range of crops that are essential for food security on a global scale. Over the years, novel stable transformation strategies loosely grouped under the term "in planta" have been proposed and validated in a large number of model (e.g. Arabidopsis and rice), major (e.g. wheat and soybean) and minor (e.g. chickpea and lablab bean) species. The in planta approach is revolutionary as it is considered genotype-independent, technically simple (i.e. devoid of or with minimal tissue culture steps), affordable, and easy to implement in a broad range of experimental settings. In this article, we reviewed and categorized over 300 research articles, patents, theses, and videos demonstrating the applicability of different in planta transformation strategies in 105 different genera across 139 plant species. To support this review process, we propose a classification system for the in planta techniques based on five categories and a new nomenclature for more than 30 different in planta techniques. In complement to this, we clarified some grey areas regarding the in planta conceptual framework and provided insights regarding the past, current, and future scientific impacts of these techniques. To support the diffusion of this concept across the community, this review article will serve as an introductory point for an online compendium about in planta transformation strategies that will be available to all scientists. By expanding our knowledge about in planta transformation, we can find innovative approaches to unlock the full potential of plants, support the growth of scientific knowledge, and stimulate an equitable development of plant research in all countries and institutions.

CRISPR/Cas9 System: A Potential Tool for Genetic Improvement in Floricultural Crops

Demand of flowers is increasing with time worldwide. Floriculture has become one of the most important commercial trades in agriculture. Although traditional breeding methods like hybridization and mutation breeding have contributed significantly to the development of important flower varieties, flower production and quality of flowers can be significantly improved by employing modern breeding approaches. Novel traits of significance have interest to consumers and producers, such as fragrance, new floral color, change in floral architecture and morphology, vase life, aroma, and resistance to biotic and abiotic stresses, have been introduced by genetic manipulation. The clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein (Cas) system has recently emerged as a powerful genome-editing tool for accurately changing DNA sequences at specific locations. It provides excellent means of genetically improving floricultural crops. CRISPR/Cas system has been utilized in gene editing in horticultural cops. There are few reports on the utilization of the CRISPR/Cas9 system in flowers. The current review summarizes the research work done by employing the CRISPR/Cas9 system in floricultural crops including improvement in flowering traits such as color modification, prolonging the shelf life of flowers, flower initiation, and development, changes in color of ornamental foliage by genome editing. CRISPR/Cas9 gene editing could be useful in developing novel cultivars with higher fragrance and enhanced essential oil and many other useful traits. The present review also highlights the basic mechanism and key components involved in the CRISPR/Cas9 system.

Current achievements and future prospects of genetic engineering in Indian mustard (Brassica juncea L. Czern & Coss.)

Transgenic technology in Indian mustard has expedited crop improvement programs. Further, there is a need to optimize gene editing protocols and find out the suitable target genes to harvest the benefits of gene editing technology in this important edible oilseed crop. Brassica juncea is an economically and industrially important oilseed crop being grown mainly in India and in some parts of Canada, Russia, China and Australia. Besides being consumed as edible oil, it also has numerous applications in food and paint industry. However, its overall production and productivity are being hampered by a number of biotic and abiotic stress factors. Further, its oil and seedmeal quality needs to be improved for increasing food as well as feed value. However, the lack of resistant crossable germplasm or varieties necessitated the use of genetic engineering interventions in Indian mustard crop improvement. A number of genes conferring resistance to biotic stresses including lectins for aphids' control, chitinase, glucanase and osmotin for disease control and for abiotic stresses, CODA, LEA and ion antiporter genes have been transferred to Indian mustard. Both antisense and RNAi technologies have been employed for improving oil and seedmeal quality. Efforts have been made to improve the phytoremediation potential of this crop through genetic engineering approach. The deployment of barnase/barstar gene system for developing male sterile and restorer lines has really expedited hybrid development programs in Indian mustard. Further, there is a need to optimize gene editing protocols and to find out suitable target genes for gene editing in this crop. In this review paper, authors have attempted to review various genetic transformation efforts carried out in Indian mustard for its improvement to combat biotic and abiotic stress challenges, quality improvement and hybrid development.

Genome-wide analysis of glycerol-3-phosphate O-acyltransferase gene family and functional characterization of two cutin group GPATs in Brassica napus

Genome-wide identification, spatio-temporal expression analysis and functional characterization of selected Brassica napus GPATs highlight their roles in cuticular wax biosynthesis and defense against fungal pathogens. Glycerol-3-phosphate 1-O-acyltransferase (GPAT) is a key enzyme in the biosynthesis of glycerolipids, a major component of cellular membranes and extracellular protective layers, such as cuticles in plants. Brassica napus is an economically important crop and cultivated worldwide mostly for its edible oil. The B. napus GPATs (BnGPATs) are insufficiently characterized. Here, we performed genome-wide analysis to identify putative GPATs in B. napus and its diploid progenitors B. rapa and B oleracea. The 32 B. napus BnGPATs are phylogenetically divided into three major groups, cutin, suberin, and diverse ancient groups. Analysis of transcriptomes of different tissues and seeds at different developmental stages revealed the spatial and temporal expression profiles of BnGPATs. The yield and oil quality of B. napus are adversely affected by the necrotrophic fungus, Sclerotinia sclerotiorum. We showed that several BnGPATs, including cutin-related BnGPAT19 and 21, were upregulated in the S. sclerotiorum resistant line. RNAi-mediated suppression of BnGPAT19 and 21 in B. napus resulted in thinner cuticle, leading to rapid water and chlorophyll loss in toluidine blue staining and leaf bleaching assays. In addition, the RNAi plants also developed severe necrotic lesions following fungal inoculation compared to the wild-type plants, indicating that BnGPAT19 and 21 are likely involved in cuticular wax biosynthesis that is critical for initial pathogen defense. Taken together, we provided a comprehensive account of GPATs B. napus and characterized BnGPAT19 and 21 for their potential roles in cuticular wax biosynthesis and defense against fungal pathogens.

Opportunities for Innovation in Genetic Transformation of Forest Trees

The incorporation of DNA into plant genomes followed by regeneration of non-chimeric stable plants (transformation) remains a major challenge for most plant species. Forest trees are particularly difficult as a result of their biochemistry, aging, desire for clonal fidelity, delayed reproduction, and high diversity. We review two complementary approaches to transformation that appear to hold promise for forest trees.

Expression of Foreign Genes Demonstrates the Effectiveness of Pollen-Mediated Transformation in Zea mays

Plant genetic transformation has arguably been the core of plant improvement in recent decades. Efforts have been made to develop in planta transformation systems due to the limitations present in the tissue-culture-based methods. Herein, we report an improved in planta transformation system, and provide the evidence of reporter gene expression in pollen tube, embryos and stable transgenicity of the plants following pollen-mediated plant transformation with optimized sonication treatment of pollen. The results showed that the aeration at 4°C treatment of pollen grains in sucrose prior to sonication significantly improved the pollen viability leading to improved kernel set and transformation efficiency. Scanning electron microscopy observation revealed that the removal of operculum covering pollen pore by ultrasonication might be one of the reasons for the pollen grains to become competent for transformation. Evidences have shown that the eGfp gene was expressed in the pollen tube and embryos, and the Cry1Ac gene was detected in the subsequent T₁ and T₂ progenies, suggesting the successful transfer of the foreign genes to the recipient plants. The Southern blot analysis of Cry1Ac gene in T₂ progenies and PCR-identified Apr gene segregation in T₂ seedlings confirmed the stable inheritance of the transgene. The outcome illustrated that the pollen-mediated genetic transformation system can be widely applied in the plant improvement programs with apparent advantages over tissue-culture-based transformation methods.

Pollen grains as a target for introduction of foreign genes into plants: an assessment

Introduction of foreign genes and development of transgenic plants have become an integral part of crop improvement programmes in the last decade. However, most of the present day plant transformation protocols require long periods for development of transgenic plants and need skilled personnel. Development of alternate, simple and rapid transformation protocols for development of transgenic plants can overcome the constraints of in vitro culture, regeneration and associated problems. Pollen grains, due to their abundance and ease with which they can be handled are ideal targets for introduction of foreign genes into the germ line. However, progress in introduction of transgenes into pollen grains and their subsequent use in fertilization leading to development of transgenic plants are limited. With the recent progress made in understanding of pollen development along with reports of successful pollen-mediated transformation in important crop plants, it should be possible to extend this simple method of transformation to other crop plants. The review deals with development of pollen grains as a target for introduction of genes with special emphasis on recent developments.