Insects surrounded by their resin seen attached on their host plant.
| Photo Credit: Special Arrangement

In a new study, researchers at the Indian Institute of Science (IISc) have unravelled the mystery behind how the lac insect produces laccaic acid that is used to make lac pigment. The lac pigment is a prized commodity used in food colouring, textiles, dyes, handicrafts, and folk art.

According to IISc, the lac insect grows on certain trees (like the flame of the forest), drinks its sugary sap, and secretes a sticky resin called shellac.

It also makes a bright red compound called laccaic acid, which is used to make the pigment. “How the insect produces laccaic acid has remained a source of mystery. For decades, scientists have unsuccessfully hunted for genes coding for its synthesis in the insect’s genome,” IISc said.

However, now the researchers have found that the colourful pigment extracted from the lac insect may actually be produced by a symbiotic yeast-like organism living inside the insect.

The team also showed that the yeast-like organism exclusively harbours genes coding for key ingredients in the pigment synthesis pathway.

India, a key producer

“For thousands of years, India has been a key producer of lac pigment. The pathway for the pigment production was not very clear,” said Shantanu Shukla, assistant professor in the Department of Developmental Biology and Genetics, IISc.

IISc said that one of the key ingredients required for laccaic acid synthesis is an amino acid called tyrosine, which the insect cannot make on its own or source from the tree sap. Such missing ingredients are usually supplied by symbiotic bacteria or fungi that live inside insect bodies and secrete these molecules in exchange for housing.

The team sequenced the entire bacterial and fungal microbiome of the insect and zeroed in on two possible candidates: a bacterium belonging to the Wolbachia genus and a yeast-like fungus. Previous studies by other researchers had hinted at the presence of the fungus but had not identified it or sequenced its genome.

In the current study, the team found that neither the insect nor the bacterium carried the genes needed to make tyrosine and other components of the pigment pathway. But the yeast-like organism did — it carried the entire set of genes needed for laccaic acid production. This includes genes coding for various enzymes which catalyse the production of aromatic molecules that are the building blocks of laccaic acid.

Inside egg cell

Mr. Shukla said that the fungus is actually inside the insect’s oocyte (egg cell). The fungus floats around in the insect’s haemolymph — the equivalent of animal blood — and as soon as the oocyte matures, it latches on to it and enters the oocyte, and gets transmitted to the offspring that emerges from the oocyte.