For the first time, a draft genome covering 374 million bases (61 per cent coverage) of the tulsi herb has been sequenced and the main enzymes responsible for the synthesis of secondary metabolites which have medicinal properties have been unravelled by a team of nearly 30 scientists at the Bengaluru-based National Centre for Biological Sciences (NCBS) and the Centre for Cellular and Molecular Platforms, Bengaluru.
Tulsi is well known for its myriad medicinal properties — antibacterial, antifungal, antipyretic, antioxidant, antiseptic and anticancer.
Of the nearly 40 secondary metabolites that have medicinal value, the genes and enzymes responsible for the production of 14 metabolites have been mapped on the genome. Not much information on the pathway is available for the remaining metabolites. Of the 14 metabolites that have been mapped, eight have anti-cancer properties and the remaining six have antifungal, antioxidant, anti-inflammatory, antiseptic, and cardio protective properties. The results were published recently in the journal BMC Plant Biology.
“We know tulsi contains many anticancer and other medicinally important properties. Now, using a genome tool we have established the genes responsible for the production of the anticancer compounds,” Ramanathan Sowdhamini from the Biochemistry and Bioinformatics Department, NCBS and one of the corresponding authors told this Correspondent by email.
Of the five tulsi subtypes investigated, only the two domesticated subtypes — Rama (green leaves) and Krishna (purple leaves) — have been found to contain very high concentration of these medicinally important metabolites. Between the two domesticated subtypes, the Rama subtype contains “high abundance” of medicinally important metabolites. “The concentration of eugenol (anti-infective) and ursolic acid (anticancer) in both leaf and stem was more in Rama than Krishna subtype,” said Atul Upadhyay the first author of the paper from NCBS.
“Ayurveda mostly uses Rama and Krishna tulsi,” said Nitish Sathyanarayana of NCBS and a co-author of the paper.
Of the various parts of the plant, the leaves were found to have the highest concentration of the metabolites; roots and stems contain only minimal amount. “While the synthesis of the metabolites appears to begin in the young leaves, the mature leaves retain the medically relevant metabolites,” said Prof. Sowdhamini.
The reason why the metabolites are most abundant in leaves could be that they are the source of energy production and they are most vulnerable to consumption by animals and exposure to pathogens.
Many of the compounds found in the tulsi plant are being evaluated for their anti-cancer properties in various clinical trials. But there is a critical limitation — the final product is isolated from the tulsi leaves. And the production of these compounds in this plant does not match large-scale commercial exploitation.
So the study opens up a horizon for commercial exploitation of the medicinally important compounds. “Since the genes that have anti-cancer properties are now known, we can engineer yeast with enzymes from tulsi to make medicinally important molecules that are normally made in tulsi,” said S. Ramaswamy, a co-author and Professor and Dean of the Institute for Stem Cell Biology and Regenerative Medicine (InStem), Bengaluru. The cost of production and the time taken to produce these compounds will come down significantly once commercial exploitation is achieved.
But can commercial production of essential metabolites be undertaken based on the latest work? “Absolutely. The wet-lab experiments carried out to follow and validate the presence of few important enzymes in tulsi would be very useful to take it forward in the commercial angle,” said Prof. Sowdhamini.