They discover how algae produce a hormone that they use to communicate

Auxin is an essential hormone for plants: it helps them grow and is responsible for the leaves pointing towards the light and the roots going deeper into the soil. It is an essential hormone in the chemical language of plants to communicate with other organisms and promote beneficial interactions. But how does it work in algae, which are the “cousins” of plants?

Although it has been known for some years that algae produce auxin, knowledge on the subject is limited and the mechanisms used by the algae to produce it had not been described.

The situation has now changed, thanks to the fact that the team of Victoria Calatrava, Aurora Galván, Ángel Llamas and Emilio Fernández, from the Inorganic Nitrogen Metabolism in Algae research group, at the University of Córdoba (UCO) in Spain, has discovered one of auxin production routes in algae, using the model algae Chlamydomonas reinhardtii.

“The auxin production pathway that we demonstrate here is very simple and very common. It involves the enzyme L-amino acid oxidase (LAO1) that produces auxin through the use of tryptophan” explains professor Aurora Galván.

The alga produces the hormone in its periplasmic space, a type of permeable membrane that is where the enzyme is located. “This is interesting because from there it can release the hormone outside to communicate with other organisms or perhaps incorporate it inside to regulate its metabolism,” continues the researcher.

Ángel Llamas, Aurora Galván and Victoria Calatrava, three of the authors of the study. (Photo: UCO)

Auxin to team up with bacteria and help agricultural production

The team has also analyzed the effects of auxin production for the algae and how the hormone helps it communicate with bacteria of the genus Methylobacterium to create beneficial interactions.

“We see that the accumulation of auxin is bad because it slows down growth. In low concentrations it improves the growth of the algae, but when it accumulates it inhibits it,” says researcher Victoria Calatrava. To solve these negative effects, Methylobacterium comes into play.

“The bacteria degrade auxin, lowering the levels of the hormone, helping Chlamydomonas to continue growing while the bacteria obtain food from the auxin,” Calatrava explains. Thus, auxin functions as a mediator in that mutualistic relationship in which algae and bacteria help each other. Furthermore, interestingly, these bacteria can feed on auxin only in the presence of the alga, which reinforces the importance of this way of cooperating.

And what applications could this knowledge have for agriculture? Recalling the importance of auxin for plants, the researcher highlights that “both algae and bacteria live in crop fields and are part of the plant microbiota, so their production and regulation of auxin could work to improve production agricultural, both its growth and tolerance to environmental stresses such as drought.

Having revealed the pathway of auxin production by algae and its role in the creation of beneficial mutualisms with bacteria, the team will now seek to find out the role of algae in the plant microbiota and more specifically the algal interaction. bacteria-plant to evaluate its potential in the development of biostimulants that benefit sustainable and environmentally friendly agricultural production.

The study is titled “Genetic evidence for algal auxin production in Chlamydomonas and its role in algal-bacterial mutualism”. And it has been published in the academic journal iScience. (Source: UCO)