Evaluation of the Chilli veinal mottle virus CP gene expressing transgenic Nicotiana benthamiana plants for disease resistance against the virus

Vegetables are an important source of income and high-value crops for small farmers. Chilli (Capsicum spp.) is one of the most economically important vegetables of Pakistan and it is grown throughout the country. It is a rich source of nutrition especially vitamins A, B, C and E along with minerals as folic acid, manganese (Mn), potassium (K) and molybdenum (Mo). Chilli possesses seven times more amount of vitamin C than an orange. Vitamin A, C and beta-carotenoids are strong antioxidants to scavenge the free radicals. Chilli production is restricted due to various biotic factors. Among these viruses, Chilli veinal mottle virus (ChiVMV) is one of the most destructive and menacing agents that inflicts heavy and colossal losses that accounted for 50% yield loss both in quality and quantity. Pathogen-Derived Resistance (PDR) approach is considered one of the effective approaches to manage plant viruses. In this study, ChiVMV was characterized on a molecular level, the coat protein (CP) gene of the virus was stably transformed into Nicotiana benthamiana plants using Agrobacterium tumefaciens. The transgenic plants were challenged with the virus to evaluate the level of resistance of plants against the virus. It was observed that the plants expressing CP gene have partial resistance against the virus in terms of symptoms’ development and virus accumulation. Translation of this technique into elite chilli varieties will be resulted to mitigate the ChiVMV in the crop as well as an economic benefit to the farmers.

Distinguishing resistances of transgenic sugarcane generated from RNA interference and pathogen‐derived resistance approaches to combating sugarcane mosaic virus

Sugarcane mosaic virus (SCMV) is a causative agent that reduces growth and productivity in sugarcane. Pathogen‐derived resistance (PDR) and RNA interference (RNAi) are the most common approaches to generating resis‐ tance against plant viruses. Two types of transgenic sugarcane have been obtained by PDR and RNAi methods using a gene‐encoding coat protein (CP) of SCMV (SCMVCp). This research aimed to distinguish resistance of the two transgenic sugarcanes in combating SCMV through artificial viral inoculation. The experiment was conducted using transgenic sugar‐ cane lines validated by PCR analysis. Insertion of gene‐encoding CP in the transgenic lines was confirmed by amplification of 702 bp of DNA fragment of SCMVCp. After viral inoculation, mosaic symptoms appeared earlier, at 21 days post inoculation (dpi) in PDR transgenic lines, but was at 26 dpi in RNAi transgenic lines. Symptom observation showed that 77.8% and 50% of the inoculated plants developed mosaic symptoms in PDR and RNAi transgenic lines, respectively. RT‐PCR analysis revealed that the nuclear inclusion protein b (Nib) gene of SCMV was amplified in the symptomatic leaves in plants classified as susceptible lines. Immunoblot analysis confirmed presence of viral CP with a molecular size of 37 kDa in the susceptible lines. Collectively, these results indicated that the RNAi approach targeting the gene for CP effectively produces more resistance against the SCMV infection in transgenic sugarcane compared to the PDR approach.

Gene silencing to induce pathogen-derived resistance in plants.

This chapter provides information on the history of the use of pathogen-derived resistance (PDR) in plants and use of PDR for basic research and commercial purposes. Some limitations of the RNA interference (RNAi) technology are presented and various tools that can be used to design RNAi constructs and screen for potential off-target effects are also discussed.

Analysis of potyvirus terminal protein VPg-transgenic Arabidopsis thaliana plants.

Virus-coded VPg protein of Potato virus Y (PVY) does not have homologs apart from other VPgs. Since VPg is indispensable for the potyvirus life cycle, it appeared a good candidate for eliciting pathogen-derived resistance to PVY. Following agroinfection used to obtain PVY VPg-transgenic Arabidopsis thaliana plants, only few transgenic seeds were recovered giving rise to six transgenic plants that contained the VPg gene with the correct sequence. They generated VPg mRNA, but VPg protein was not detected. Some plants were immune to PVY infection suggesting post-transcriptional gene silencing. However, the likely PVY VPg toxicity exerted at an early stage of transformed seeds development precludes its use for engineering pathogen-derived resistance.

Genetic Engineering for Viral Disease Management in Plants

Viral diseases are a major threat to world agriculture and breeding resistant varieties against these viruses is one of the major challenge faced by plant virologists and biotechnologists. The development of the concept of pathogen derived resistance gave rise to strategies ranging from coat protein based interference of virus propagation to RNA mediated virus gene silencing. Much progress has been achieved in protecting plants against these RNA and DNA viruses. In this review, the most recent transgene based approaches for viral disease management in plants will be discussed.

Twenty Years of Transgenic Plants Resistant to Cucumber mosaic virus

Plant genetic engineering has promised researchers improved speed and flexibility with regard to the introduction of new traits into cultivated crops. A variety of approaches have been applied to produce virus-resistant transgenic plants, some of which have proven to be remarkably successful. Studies on transgenic resistance to Cucumber mosaic virus probably have been the most intense of any plant virus. Several effective strategies based on pathogen-derived resistance have been identified; namely, resistance mediated by the viral coat protein, the viral replicase, and post-transcriptional gene silencing. Techniques using non-pathogen-derived resistance strategies, some of which could offer broader resistance, generally have proven to be much less effective. Not only do the results obtained so far provide a useful guide to help focus on future strategies, but they also suggest that there are a number of possible mechanisms involved in conferring these resistances. Further detailed studies on the interplay between viral transgene-derived molecules and their host are needed in order to elucidate the mechanisms of resistance and pathogenicity.