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Tobacco has been widely used as a model plant for stable and non-stable gene function analysis. Successful Agrobacterium-mediated transformation mainly depends on in vitro regeneration of tobacco plant. However, a reliable and standard regeneration protocol of tobacco using multiple explants is limited. In this study, we established a reliable and reproducible regeneration protocol of tobacco using three different explants i.e. cotyledon, hypocotyl and leaf. Preliminary, surface sterilized tobacco seeds were germinated on growth regulator free MS medium. Thereafter, in vitro germinated explants were inoculated into Murashige and Skoog [1] media supplemented with different combination and types of growth regulators for callus induction and subsequent regeneration of plantlets. It was revealed that, regeneration ability of explants is greatly influenced by type and nature of the explant. Among the three explants, higher callus induction (95%) was obtained in MS medium supplemented with 2.0 mg l-1 kinetin + 2.0 mg l-1 IAA from leaf explant. Also, leaf explant exhibited much higher regeneration ability (95%) than hypocotyl (60%) and cotyledon (45%) explants. Significantly highest number of shoots (8.0) were regenerated from leaf explants cultured on MS medium supplemented with 3.0 mg l-1 Kinetin+1.0 mg l-1 IAA compared to the other hormone combinations. Regenerated mature shoots were showed normal root after transferred onto ½ MS medium containing 0.3 mg l-1 IBA. This study will provide valuable information related to in vitro regeneration of tobacco plantlets using cotyledon, hypocotyl and leaf explants and will be used as a standard protocol for Agrobacterium-mediated transformation for gene function analysis.

RNA silencing is mediated through RNA interference (RNAi) pathway gene families, i.e., Dicer-Like (DCL), Argonaute (AGO), and RNA-dependent RNA polymerase (RDR) and their cis-acting regulatory elements. The RNAi pathway is also directly connected with the post-transcriptional gene silencing (PTGS) mechanism, and the pathway controls eukaryotic gene regulation during growth, development, and stress response. Nevertheless, genome-wide identification of RNAi pathway gene families such as DCL, AGO, and RDR and their regulatory network analyses related to transcription factors have not been studied in many fruit crop species, including banana (Musa acuminata). In this study, we studied in silico genome-wide identification and characterization of DCL, AGO, and RDR genes in bananas thoroughly via integrated bioinformatics approaches. A genome-wide analysis identified 3 MaDCL, 13 MaAGO, and 5 MaRDR candidate genes based on multiple sequence alignment and phylogenetic tree related to the RNAi pathway in banana genomes. These genes correspond to the Arabidopsis thaliana RNAi silencing genes. The analysis of the conserved domain, motif, and gene structure (exon-intron numbers) for MaDCL, MaAGO, and MaRDR genes showed higher homogeneity within the same gene family. The Gene Ontology (GO) enrichment analysis exhibited that the identified RNAi genes could be involved in RNA silencing and associated metabolic pathways. A number of important transcription factors (TFs), e.g., ERF, Dof, C2H2, TCP, GATA and MIKC_MADS families, were identified by network and sub-network analyses between TFs and candidate RNAi gene families. Furthermore, the cis-acting regulatory elements related to light-responsive (LR), stress-responsive (SR), hormone-responsive (HR), and other activities (OT) functions were identified in candidate MaDCL, MaAGO, and MaRDR genes. These genome-wide analyses of these RNAi gene families provide valuable information related to RNA silencing, which would shed light on further characterization of RNAi genes, their regulatory elements, and functional roles, which might be helpful for banana improvement in the breeding program.