ABSTRACT
The full length Andrographis paniculate 4-hydroxy 3-methyl 2-butenyl 4-diphosphate reductase (ApHDR) gene of MEP pathway was isolated for the first time. The ApHDR ORF with 1404 bp flanked by 100 bp 5'UTR and 235 bp 3'UTR encoding 467 amino acids (NCBI accession number: MK503970) and cloned in pET 102, transformed and expressed in E. coli BL21. The ApHDR protein physico-chemical properties, secondary and tertiary structure were analyzed. The Ramachandran plot showed 93.8% amino acids in the allowed regions, suggesting high reliability. The cluster of 16 ligands for binding site in ApHDR involved six amino acid residues having 5-8 ligands. The Fe-S cluster binding site was formed with three conserved residues of cysteine at positions C123, C214, C251 of ApHDR. The substrate HMBPP and inhibitors clomazone, paraquat, benzyl viologen's interactions with ApHDR were also assessed using docking. The affinity of Fe-S cluster binding to the cleft was found similar to HMBPP. The HPLC analysis of different type of tissue (plant parts) revealed highest andrographolide content in young leaves followed by mature leaves, stems and roots. The differential expression profile of ApHDR suggested a significant variation in the expression pattern among different tissues such as mature leaves, young leaves, stem and roots. A 16-fold higher expression of ApHDR was observed in the mature leaves of A. paniculata as compared to roots. The young leaves and stem showed 5.5 fold and fourfold higher expression than roots of A. paniculata. Our result generated new genomic information on ApHDR which may open up prospects of manipulation for enhanced diterpene lactone andrographolide production in A. paniculata. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s12298-021-00952-0.
ABSTRACT
Andrographis paniculata 1-deoxy-D-xylulose-5-phosphate synthase (ApDXS) gene (GenBank Accession No MG271749.1) was isolated and cloned from leaves for the first time. Expression of ApDXS gene was carried out in Escherichia coli Rosetta cells. Tissue-specific ApDXS gene expression by quantitative RT-PCR (qRT-PCR) revealed maximum fold expression in the leaves followed by stem and roots. Further, the differential gene expression profile of Jasmonic acid (JA)-elicited in vitro adventitious root cultures showed enhanced ApDXS expression compared to untreated control cultures. A. paniculata 3-hydroxy-3-methylglutaryl-coenzyme A reductase (ApHMGR) gene expression was also studied where it was up-regulated by JA elicitation but showed lower expression compared to ApDXS. The highest expression of both genes was found at 25 µm JA elicitation followed by 50 µm. HPLC data indicated that the transcription levels were correlated with increased andrographolide accumulation. The peak level of andrographolide accumulation was recorded at 25 µM JA (9.38-fold) followed by 50 µM JA (7.58-fold) in elicitation treatments. The in silico generated ApDXS 3D model revealed 98% expected amino acid residues in the favored and 2% in the allowed regions of the Ramachandran plot with 92% structural reliability. Further, prediction of conserved domains and essential amino acids [Arg (249, 252, 255), Asn (307) and Ser (247)] involved in ligand/inhibitor binding was carried out by in silico docking studies. Our present findings will generate genomic information and provide a blueprint for future studies of ApDXS and its role in diterpenoid biosynthesis in A. paniculata.
