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Transcription factors are multi-domain proteins that regulate gene expression in eukaryotic organisms. They are one of the largest families of proteins, which are structurally and functionally diverse. While there are transcription factors that are plant-specific, such as AP2/ERF, B3, NAC, SBP and WRKY, some transcription factors are present in both plants as well as other eukaryotic organisms. MYB transcription factors are widely distributed among all eukaryotes. In plants, the MYB transcription factors are involved in the regulation of numerous functions such as gene regulation in different metabolic pathways especially secondary metabolic pathways, regulation of different signalling pathways of plant hormones, regulation of genes involved in various developmental and morphological processes etc. Out of the thousands of MYB TFs that have been studied in plants, the majority of them have been studied in the model plants like Arabidopsis thaliana, Oryza sativa etc. The study of MYBs in other plants, especially medicinal plants, has been comparatively limited. But the increasing demand for medicinal plants for the production of biopharmaceuticals and important bioactive compounds has also increased the need to explore more number of these multifaceted transcription factors which play a significant role in the regulation of secondary metabolic pathways. These studies will ultimately contribute to medicinal plants’ research and increased production of secondary metabolites, either through transgenic plants or through synthetic biology approaches. This review compiles studies on MYB transcription factors that are involved in the regulation of diverse functions in medicinal plants.

In the current study, a MYB (Myeloblastosis) Transcription Factor (TF) gene sequence ( WsMYB46 ) has been retrieved from the transcriptome repertoire of the medicinal plant Withania somnifera and it has been structurally and functionally characterised using different bioinformatics tools. Amino acid sequence comparison of WsMYB46 and MYB TFs from 30 medicinal plants and the model plant Arabidopsis thaliana provided information about the conserved DNA binding domains of WsMYB46. The analysis suggests that WsMYB46 belongs to the R2R3 family of MYB TFs. The in silico prediction of the physicochemical properties of WsMYB46 and the MYB TFs show that they are localized in the nucleus, contain 312–438 amino acid residues, and are hydrophilic and acidic in nature, with a theoretical pI between 5.15 and 6.65. A 3-D model of the WsMYB46 protein has been constructed, and the functional annotation indicates that the WsMYB46 gene is involved in mRNA and cellular processing. The high degree of structural similarity of WsMYB46 with AtMYB46/AtMYB83, which are known to have important roles in the regulation of secondary cell wall biosynthesis, indicates the possible functional role of WsMYB46 in the regulation of secondary cell wall biosynthesis. The in silico gene expression analysis showed its low expression during salt stress. 427 miRNA sequences from A. thaliana were selected to identify the possible miRNA targets in WsMYB46. Six miRNAs with target sites in WsMYB46 were identified. This comprehensive in silico study of WsMYB46 and other MYB TFs from medicinal plants would be helpful to gain a deeper understanding of MYB TFs and their roles in medicinal plants.

Tma12, isolated from the fern Tectaria macrodonta, is a next-generation insecticidal protein. Transgenic cotton expressing Tma12 exhibits resistance against whitefly and viral diseases. Beside its insecticidal property, the structure and function of Tma12 are unknown. This limits understanding of the insecticidal mechanism of the protein and targeted improvement in its efficacy. Here we report the amino acid sequence analysis and the crystal structure of Tma12, suggesting that it is possibly a lytic polysaccharide monooxygenase (LPMO) of the AA10 family. Amino acid sequence of Tma12 shows 45% identity with a cellulolytic LPMO of Streptomyces coelicolor. The crystal structure of Tma12, obtained at 2.2 Å resolution, possesses all the major structural characteristics of AA10 LPMOs. A H₂O₂-based enzymatic assay also supports this finding. It is the first report of the occurrence of LPMO-like protein in a plant. The two facts that Tma12 possesses insecticidal activity and shows structural similarity with LPMOs collectively advocate exploration of microbial LPMOs for insecticidal potential.

Gabapentin (1-(aminomethyl)cycloheaxaneacetic acid; Gpn) is a widely used anti-epileptic drug. The target site of action of Gpn remains controversial. Gpn can exist in two isomeric chair forms. The crystal structures of Gpn 1 and eight derivatives, Gpn hydrochloride 2, Gpn lactam 3, Boc-Gpn-OH 4, Ac-Gpn-OH 5, PivGpn-OH 6, Tosyl-Gpn-OH 7, Boc-Gpn-OSu 8 and Boc-Gpn-NHMe 9, are described. The aminomethyl group occupies an axial position in 1, 3, 6 and 7, while it lies in an equatorial orientation in 2, 4, 5 and 8. The structure of Boc-Gpn-NHMe 9 reveals that the crystals contain both chair forms of the derivative in the ratio 0.7 : 0.3, favouring the aminomethyl group in an axial position. In all cases, the torsional angles about the Cα-Cβ (θ1) and Cβ-Cγ (θ2) bonds of the γ-amino acid residue are characteristic of a gauche, gauche (g, g) conformation. In solution, NMR studies establish rapid conformational exchange, as anticipated, at room temperature. Low temperature NMR studies permit conformational freezing and determination of the freeenergy difference between the two 1,1-disubstituted cyclohexane conformers. The largest free-energy difference is observed in the free amino acid (0.38 Kcal mol-1), with the most stable conformer having the aminomethyl group in the equatorial position. The free-energy difference between the two forms is significantly reduced in the protected derivatives, with almost equal populations observed in solution for the fully protected neutral derivatives, Boc-Gpn-NHMe and Gpn lactam.