Through the shot glass, and what can be found in liverworts

Studying plant vegetative reproduction is key to increasing crop yield and for bioengineering. Kobe University research is making progress in studying the genetic regulation of the process in liverworts, which are ideal model plants and even a candidate for space crops.

Potatoes are tubers, ginger is a rhizome, and both are forms of vegetative plant reproduction, in which plants create structures from which genetically identical individuals can emerge. This mode of reproduction is very important for agriculture and horticulture, but there is very little research on the underlying genetic mechanism.

Kobe University plant geneticist Ishizaki Kimitsune thinks that the liverwort Marchantia polymorpha is an ideal model organism to study this process, and over the past 10 years, has been involved in decoding its genome and establishing tools for its convenient genetic manipulation.

He says, “The liverwort is so proliferative that it is considered a nuisance to gardeners, growing back quickly no matter how often it is removed.”

The liverwort spreads through tiny, detachable buds, called “gemmae,” that form in small cups on the upper side of the liverwort’s “leaves” and are dispersed by rain, the wind or animals. Apart from this, the plant also engages in sexual production, switching from vegetative reproduction when the days become longer in summer.

“In previous research, we found a gene that seemed to be involved in the formation of both gemma cups and the plant’s sexual reproductive organs. But it was completely unclear what it does, so we wanted to learn more,” says Ishizaki.

In the journal New Phytologist, the Kobe University team now reports that plants lacking the gene generally don’t form vegetative or sexual reproductive organs, and in rare cases form empty, shot-glass-shaped cups instead of the usually wide and shallow gemma cups, leading them to name the gene “shot glass.” This shows that the gene is necessary for the development of functioning reproductive structures.

Studying the interactions with other genes known to be involved, the team found that shot glass acts by suppressing the development of air chambers in the liverwort’s “leaves” to make space for gemma cup development, and by helping factors needed for the development of sexual reproductive organs to locate to the right place.

In addition, Ishizaki and his team found something astonishing. They knew that flowering plants, which are much more complex than the simple liverwort, have genes that are related to shot glass and likely derive from the same gene in the ancestor of all land plants. Interestingly, in flowering plants, those genes are also involved in regulating the development of the secondary meristem that—broadly speaking—makes a plant grow branches.

When they inserted the liverwort’s gene into a flowering plant lacking one of its own versions, they found that it could even compensate for the gap its more evolved cousin left.

Ishizaki explains, “This suggests that the mechanism by which plants create new buds away from the main shoot tip may be common to all land plants.”

This means that Ishizaki’s liverwort is indeed a convenient model organism to study this agriculturally important process. But the Kobe University researcher has bigger dreams.

“Unlike crop plants, liverworts don’t require soil but can be grown with just fog cultivation. We are exploring the development of liverworts where the whole body is directly available as a food resource. This means it could even be used as a food source in space,” Ishizaki explains.

“We are also exploring using the liverwort as an organism for the bioproduction of valuable chemical resources, which has so far practically been restricted to bacteria and yeasts. The engineering technology we are developing and the knowledge we are gathering on the plant’s biology are an important step in that direction.”