How does catnip maintain its “cat-attracting physique”?

Sneezing, chewing, rubbing, rolling, meowing, holding hands, chasing imaginary mice, sitting still and staring...

These are the possible reactions that cats may have after eating catnip (Nepeta cataria, catmint). The reason why catnip can attract cats is because of one of its ingredients, nepetalactone.

Recently, a group of researchers from the University of York in the UK, Purdue University in the United States, the University of Florida, Michigan State University, and the Max Planck Institute for Chemical Ecology in Germany discovered the past and present of nepetalactone.

On May 13, 2020, the team's paper titled The evolutionary origins of the cat attractant nepetalactone in catnip was published online in Science Advances.

Catnip has a long history. It was first mentioned in 1753 in the book Species Plantarum by Swedish biologist Carl von Linné.

In fact, catnip has many names, such as camphor grass, cool mint, catnip, mint, mint, anise, nepeta, and esculenta, etc. It is a plant of the genus Nepeta and the family Lamiaceae.

As the name suggests, catnip has a unique appeal to cats. In fact, not only cats, but also tigers, leopards, jaguars, cheetahs, lynxes and other felines are basically affected by this plant and produce hallucinations.

It is understood that catnip does have a certain positive effect in avoiding loneliness and depression in cats and relieving their stress. Therefore, there are many cat toys filled with catnip on the market. Catnip can also help cats vomit the hair balls that cannot be digested in their stomachs, but the real use of catnip is to repel insects.

In catnip, a volatile metabolite called nepetalactone, which looks like white powder crystals, is the main ingredient that excites cats.

Leifeng.com noticed that the process by which catnip affects cats is roughly as follows:

In the cat's olfactory epithelium, nepetalactone binds to one or more olfactory receptors, thereby activating the amygdala in the brain and converting it into behavioral signals. The signals also regulate the cat's neuroendocrine responses through the hypothalamus and the pituitary gland.

The figure below shows the volatile nepetalactone stereoisomers found in the genus Nepeta.

The chemical, nepetalactone, was first isolated in 1941 by steam distillation and is a volatile iridoid produced by catnip.

It is worth noting that according to the International Code of Plant Nomenclature, green plants (including fungi) include 12 main levels (classes), including family and genus. The genus belongs to the family, and a family contains one or more genera.

Leifeng.com learned that the Nepetae subfamily includes many common plants, such as basil, rosemary and mint.

As shown in the figure below, researchers found that cyclopentadiene terpenes are present in many Lamiaceae plants, but once disappeared during the evolution of Nepetoideae (a subfamily of the genus Nepeta), but then reappeared, mainly in the form of volatile nepetalactones.

But there is an exception to this rule and that is catnip - that is, catnip has always produced nepetalactone, while some of its "close relatives" have seen nepetalactone disappear and reappear.

Based on this discovery, the research team used comparative genomics, ancestral sequence reconstruction and phylogenetic analysis to explore the biosynthesis of cyclopentadiene in Nepeta plants.

Specifically, the researchers sequenced the genomes of two species of catmint and hyssop (Hyssopus officinalis, which does not produce any iridoids, including nepenthesin).

Ultimately, this study found evidence for the sequence of events that led to the formation of nepetalactone biosynthesis and its metabolic gene cluster (loss of cyclopentadiene 55-65 million years ago), thus revealing the loss-reevolution mechanism of cyclopentadiene in the Nepeta lineage.

The researchers found that about 20 million years ago, an ancestor of the genus Nephrolepis began to evolve two enzymes, ISY and NEPS. These two enzymes responsible for producing nephrolepis lactone molecules are only found in catnip and are not found in any "closely related" plants.

As Benjamin Lichman of York University, the paper’s lead author, said:

We discovered an unusual set of enzymes that produce the molecule nepetalactone. These enzymes have evolved a unique mechanism only in catnip. When we first saw the catnip genome sequence, we realized that the genes that we hypothesized to be important in the formation of nepetalactone were next to each other in the genome.

It is worth mentioning that Nepeta has become an important model for studying the loss-reevolution of a major class of defensive compounds, and this study also provides insights into the interaction between enzyme and genome evolution in the origin, disappearance and re-emergence of plant chemical diversity.

As Sarah O'Connor, director of the Natural Product Biosynthesis Department at the Max Planck Institute for Chemical Ecology in Germany, said:

This provides a good example for studying the evolution of plant diversity. We are now trying to artificially change the chemical composition of Nepeta plants. This will help us understand whether we have fully understood the path of all plant evolution and the ecological function of nepetalactones. This in turn can help us reveal the biological selective pressures that led to this process. In addition, we are also looking for other Nepeta plants that produce unusual iridoids.

Source:

[1]https://advances.sciencemag.org/content/6/20/eaba0721

[2]https://www.zhihu.com/topic/20746118/intro

[3]https://phys.org/news/2020-05-mint-catmint.html

[4]https://baike.baidu.com/item/%E7%8C%AB%E8%96%84%E8%8D%B7/1677283?fr=aladdin#6