Indian holy basil hot favourite of genomic scientists

Holy basil plant tulsi seems to be a hot favourite of genomic scientists in the country this year as two separate groups of scientists – one from the CSIR-Central Institute of Medicinal & Aromatic Plants (CSIR-CIMAP), Lucknow and another from the National Centre for Biological Sciences (NCBS), Bangalore – report sequencing the whole genomes of two different varieties of the sacred Indian plant.

While CIMAP scientists published the whole genome sequence of Ocimum sanctum¹, worshipped by Hindus as ‘Vishnupriya’, in June this year, NCBS scientists produced the first draft genome of O. tenuiflorum or the ‘Krishna’ subtype this week (September 2015)².

Both genomes open up the immense medical, metabolic and therapeutic potential of the much revered herb described in ancient Indian Ayurvedic text Charaka Samhita as the “Queen of herbs”. Ocimum varieties are widely used in traditional Greek, Roman, Siddha and Unani systems of medicine.

Tulsi is rich in phenylpropanoids, terpenoids and their derivatives, known for their therapeutic roles. “The availability of the genome sequence now opens the possibility to identify genes involved in producing therapeutic molecules and to produce them in vitro ,” says Ajit Kumar Shasany, corresponding author of the CIMAP project carried out with Bengaluru-based genomics company Genotypic. The draft genome will also facilitate identification of not yet identified genes involved in the synthesis of important secondary metabolites in this plant,” he adds.

The genomic data could also be used for the production of secondary metabolites through synthetic biology approaches. Comparing the genomic data, the scientists found that O. sanctum showed maximum evolutionary closeness to Salvia miltiorrhiza , a plant used in the Chinese system of traditional medicine.

Working on Ocimum tenuiflorum, the NCBS group led by Sowdhamini has produced the first draft genome of the Krishna subtype. The team included researchers from NCBS, inStem and CCAMP, all members of the Bangalore Life Sciences Cluster.

Sowdhamini says since the genes involved in the synthesis of secondary metabolites of medicinal value are now known, it is possible to engineer a convenient model organism to overproduce such enzymes from tulsi.

On the new avenues of inquiry that the genomic data opens up, Sowdhamini says detailed comparison and characterisation of select tulsi genes will now become possible to understand the medicinal values. The medicinal properties of tulsi are attributed to specialised compounds produced as a part of its defence mechanism. These compounds are called 'metabolites' because they are a by-product of the plant's metabolism. “There are more than 40 secondary metabolites in Ocimum species, which are exploited by humans to treat diseases.

“Apigenin, taxol and urosolic acid are known to impart anti-cancer properties while citral is an anti-septic and eugenol has anti-infective properties”, says Atul Updadhyay, the first author of the Bangalore cluster paper.

The team used five different types of Tulsi, (Ocimum tenuflorium subtype Rama, O. tenuflorium subtype Krishna, O. gratissimum , O. saccharicum and O. kilmund) to collect the genomic data. They then compared the results with well-studied species like Arabidopsis thaliana . This helped them identify the unique compounds found in tulsi Krishna subtype. They also investigated an important metabolic pathway producing urosolic acid, which revealed that such specialised metabolites are synthesised in the young tissues and carried onto the matured parts, while retaining their medicinal properties.