Sagar Banerjee

Contemporary Understanding of miRNA-Based Regulation of Secondary Metabolites Biosynthesis in Plants

Plants secondary metabolites such as flavonoids, terpenoids, and alkaloids etc. are known for their role in the defense against various insects-pests of plants and for medicinal benefits in human. Due to the immense biological importance of these phytochemicals, understanding the regulation of their biosynthetic pathway is crucial. In the recent past, advancement in the molecular technologies has enabled us to better understand the proteins, enzymes, genes, etc. involved in the biosynthetic pathway of the secondary metabolites. miRNAs are magical, tiny, non-coding ribonucleotides that function as critical regulators of gene expression in eukaryotes. Despite the accumulated knowledge of the miRNA-mediated regulation of several processes, the involvement of miRNAs in regulating secondary plant product biosynthesis is still poorly understood. Here, we summarize the recent progress made in the area of identification and characterizations of miRNAs involved in regulating the biosynthesis of secondary metabolites in plants and discuss the future perspectives for designing the viable strategies for their targeted manipulation.

RNA Interference: A Novel Source of Resistance to Combat Plant Parasitic Nematodes

Plant parasitic nematodes cause severe damage and yield loss in major crops all over the world. Available control strategies include use of insecticides/nematicides but these have proved detrimental to the environment, while other strategies like crop rotation and resistant cultivars have serious limitations. This scenario provides an opportunity for the utilization of technological advances like RNA interference (RNAi) to engineer resistance against these devastating parasites. First demonstrated in the model free living nematode, Caenorhabtidis elegans; the phenomenon of RNAi has been successfully used to suppress essential genes of plant parasitic nematodes involved in parasitism, nematode development and mRNA metabolism. Synthetic neurotransmitants mixed with dsRNA solutions are used for in vitro RNAi in plant parasitic nematodes with significant success. However, host delivered in planta RNAi has proved to be a pioneering phenomenon to deliver dsRNAs to feeding nematodes and silence the target genes to achieve resistance. Highly enriched genomic databases are exploited to limit off target effects and ensure sequence specific silencing. Technological advances like gene stacking and use of nematode inducible and tissue specific promoters can further enhance the utility of RNAi based transgenics against plant parasitic nematodes.

Pathogenicity, Ecology and Genetic Diversity of the Fusarium spp. Associated with an Emerging Bakanae Disease of Rice ( Oryza sativa L.) in India

Bakanae disease is one of the emerging diseases of rice (Oryza sativa L.). Gibberella fujikuroi species complex were detected in popularly grown rice varieties of India with infection percentage ranging from 1 to 24 %. Pathogenicity test of Fusarium spp. was performed in susceptible rice variety Pusa 1121, which showed reduced seed germination and possessed varying ability to cause symptoms. On the basis of internal transcribed spacer (ITS) and Translation Elongation Factor (TEF), three Fusarium spp., viz. F. verticillioides, F. fujikuroi and F. proliferatum were found associated with bakanae disease of rice in India. Maximum numbers of slender and chlorotic leaves were produced by F. fujikuroi (90 %), whereas crown rot and stem rot was produced by F. verticillioides (50 %). F. proliferatum produced both elongation and rotting symptoms. Information on the bakanae disease, its distribution, characterization and identification in India could be helpful for the development of management strategies.

Small Noncoding RNA-Based Regulation of Plant Immunity

Plant pathogens trigger massive changes in plant gene expression in the host as a result of transcriptional reprogramming. This activates several defense-related pathways such as hormonal imbalances, signal transduction, induction of defense-related proteins, ROS generation, small RNA expression, etc.; small RNA regulates myriad biological processes in several eukaryotes constituting a vital group of gene expression regulators. Among all, plants utilize small noncoding RNA machinery as a crucial means to respond and defend against pathogens by regulating immune-responsive genes. In turn, phytopathogens have evolved various effector molecules such as proteins and recently discovered sRNAs of fungal origin delivered into host cells to suppress plant immunity, to counter-defend the effect of host small RNA machinery. The significance of the small RNA-mediated plant defense response during plant-pathogen interaction have been well-established. Here, we discuss findings on noncoding small RNAs (sRNAs) from plants and pathogens, which regulate host immunity and pathogen virulence.

Host Delivered RNAi of Two Cuticle Collagen Genes, Mi-col-1 and Lemmi-5 Hampers Structure and Fecundity in Meloidogyne incognita

Root-knot nematodes have emerged as devastating parasites causing substantial losses to agricultural economy worldwide. Tomato is the most favored host for major species of root-knot nematodes. Control strategies like use of nematicides have proved to be harmful to the environment. Other control methods like development of resistant cultivars and crop rotation have serious limitations. This study deals with the application of host generated RNA interference toward development of resistance against root-knot nematode Meloidogyne incognita in tomato. Two cuticle collagen genes viz. Mi-col-1 and Lemmi-5 involved in the synthesis and maintenance of the cuticle in M. incognita were targeted through host generated RNA interference. Expression of both Mi-col-1 and Lemmi-5 was found to be higher in adult females followed by egg masses and J2s. Tomato var. Pusa Ruby was transformed with the RNAi constructs of these genes to develop transgenic lines expressing the target dsRNAs. 30.80–35.00% reduction in the number of adult females, 50.06–65.73% reduction in the number of egg mass per plant and 76.47–82.59% reduction in the number of eggs per egg mass were observed for the T1 events expressing Mi-col-1 dsRNA. Similarly, 34.14–38.54% reduction in the number of adult females, 62.34–66.71% reduction in number of egg mass per plant and 67.13–79.76% reduction in the number of eggs per egg mass were observed for the T1 generation expressing Lemmi-5 dsRNA. The multiplication factor of M. incognita reduced significantly in both the cases and the structure of adult females isolated from transgenic plants were heavily distorted. This study demonstrates the role of the cuticle collagen genes Mi-col-1 and Lemmi-5 in the structure and development of M. incognita cuticle inside the host and reinforces the potential of host generated RNA interference for management of plant parasitic nematodes (PPNs).