RNA dependent RNA polymerase (RdRp) is one of the most versatile enzymes of RNA viruses that is indispensable for replicating the genome as well as for carrying out transcription. The core structural features of RdRps are conserved, despite the divergence in their sequences. The structure of RdRp resembles that of a cupped right hand and consists of fingers, palm and thumb subdomains. The catalysis involves the participation of conserved aspartates and divalent metal ions. Complexes of RdRps with substrates, inhibitors and metal ions provide a comprehensive view of their functional mechanism and offer valuable insights regarding the development of antivirals. In this article, we provide an overview of the structural aspects of RdRps and their complexes from the Group III, IV and V viruses and their structure-based phylogeny.

Badnaviruses (Family: Caulimoviridae; Genus: Badnavirus) are non-enveloped bacilliform DNA viruses with a monopartite genome containing about 7.2 to 9.2 kb of dsDNA with three to seven open reading frames. They are transmitted by mealybugs and a few species by aphids in a semi-persistent manner. They are one of the most important plant virus groups and have emerged as serious pathogens affecting the cultivation of several horticultural crops in the tropics, especially banana, black pepper, cocoa, citrus, sugarcane, taro, and yam. Some badnaviruses are also known as endogenous viruses integrated into their host genomes and a few such endogenous viruses can be awakened, e.g., through abiotic stress, giving rise to infective episomal forms. The presence of endogenous badnaviruses poses a new challenge for the fool-proof diagnosis, taxonomy, and management of the diseases. The present review aims to highlight emerging disease problems, virus characteristics, transmission, and diagnosis of badnaviruses.

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Sixteen collections of the wild Musa species, Musa balbisiana Colla collected from different regions of India were studied for their intraspecific relationships using random amplified polymorphic DNA (RAPD) markers. Out of 80 primers screened, 34 primers produced reproducible bands and four primers among them showing polymorphic bands were used. In all, 43 DNA fragments were amplified averaging 10.75 per primer. Of these, 31 amplified fragments showed polymorphism (averaging of 7.75 per primer). The extent of polymorphism (74.6%) has indicated the existence of considerable variation at the DNA level within the species. The 16 accessions were clustered into four as against seven clusters obtained through morphotaxonomic characterization. The inter relationships based on geographical origin in comparison with molecular characterization have been discussed.

A B S T R A C TVirus infection can result in the alteration of physiological, biochemical and metabolic processes within plants leading to symptom development. Banana bunchy top virus (BBTV) is one of the most destructive viral diseases in Tropical Asia, Pacific Indian Oceania (PIO) regions and Africa leading to 100% yield loss in banana and plantains. Though molecular characterization and their diversity were studied in depth in recent years, information on physiological and biochemical changes during banana-BBTV interaction is still not convincingly explained. Therefore, the present investigation was conducted to find out the quantifiable changes in physiological and biochemical parameters such as proteins, pigment and carbohydrate content, phenolic compounds, polyphenol oxidase (PPO), peroxidase (POX), ascorbate peroxidase (APX), guaiacol peroxidase (GPX), catalase (CAT) and superoxide dismutase (SOD) activities in leaves of banana cultivars Grand Nain (AAA) and Virupakshi (AAB). The amount of carbohydrate contents, phenolic compounds, PPO, POX, APX, GPX, CAT were significantly higher in BBTV infected leaves of both the cultivars over the healthy, whereas total protein content, pigments and SOD activity showed an opposite trend. Overall the results suggest that BBTV infection induces significant changes in enzyme levels leading to irreversible symptom development. Further studies would lead to identification of biochemical markers for studying plant-virus compatible and incompatible interactions.