An international study led by researchers from the Higher Council for Scientific Research (CSIC) has identified a new plant hormone key to the survival of plants. It is the hormone dinor-OPDA, which allows non-vascular plants (bryophytes) to defend themselves from their external aggressors, such as pathogens and insects, among others. The study is on the cover of the journal Nature Chemical Biology.
"In addition to identifying the plant hormone, we have understood its biosynthetic pathway and demonstrated the functional conservation of its molecular signalling pathway (the molecular steps necessary for the hormone to activate the plant's defences)," explains Roberto Solano, researcher of the CSIC in the National Centre of Biotechnology, who has led the study.
The study initially aimed to find out how bryophytes (non-vascular plants) defend themselves from their external aggressors. The defence mechanism of the rest of terrestrial plants (the vascular ones) was known; it is based on jasmonates, a type of phytohormones essential for the survival of the plants, because they protect them from different types of stress (pathogens, insects, etc.). "The active form of this hormone (jasmonoyl-isoleucine) was discovered by our group a few years ago in the plant Arabidopsis thaliana," says Solano. However, this hormone, which has been detected in many other vascular plants, does not exist in bryophytes (non-vascular plants), so it was not clear how these defended themselves from their external aggressors.
This study has now managed to identify the hormonal defence mechanism of bryophyte plants by conducting research on the liverwort plant Marchantia polymorpha. "Liverworts are a type of bryophyte that are considered representatives of the first plants that colonised the Earth," explains Isabel Monte, first author of the study. "Using this plant, we have shown that the molecular signalling system of the jasmonoyl-isoleucine hormone is preserved in bryophytes, but the hormone that activates this route is different from that of vascular plants," says the researcher.
"The most important aspect of the work is that we have identified this new hormone as two isomers of dinor-OPDA (dinor-cis-OPDA and dinor-iso-OPDA), which would be the equivalent in bryophytes of the jasmonoyl-isoleucine of vascular plants. Moreover, we have also understood its biosynthesis and signalling path," says Solano.
The study also reaches other conclusions of interest. "Since the Marchantia polymorpha is considered a current representative of the first plants that colonised the Earth, our discovery suggests that the 'ancestral' hormone, that is, the hormone present in that common ancestor to all terrestrial plants, was the dinor-OPDA, whereas jasmonoyl-isoleucine is a recent creation of vascular plants which appeared in the process of evolution," argues Solano. "Furthermore, although the hormone discovered exists in vascular plants, until now it had been considered only a precursor of the jasmonoyl-isoleucine hormone. Our work suggests that the new hormone could also have a hormonal function in vascular plants, attributed until now to jasmonoyl-isoleucine, and which we want to characterise in future studies," explains Solano.
At the same time, this work also confirms that the study of phylogenetically distant organisms, such as Marchantia polymorpha
, can facilitate rapid progress in the knowledge about the fundamental processes in any plant, concludes Solano.