Auxin is a hormone that is fundamental for plants, as it helps them grow and is responsible for their leaves seeking exposure to light, and their roots reaching down into the soil. It is an essential hormone in the chemical language of plants, enabling them to communicate with other organisms and promoting beneficial interactions. But, how does it work in algae, which are 'cousins' of plants?
Although it has been known for some years that algae produce auxin, knowledge of the subject is limited and the mechanisms used by algae to produce it had not been described. Now, researchers Victoria Calatrava, Aurora Galván, Ángel Llamas and Emilio Fernández, with the Inorganic Nitrogen Metabolism in
Algae research group at the University of Cordoba, have discovered one of the routes of auxin production in algae, using Chlamydomonas reinhardtii algae as a model.
"The auxin production pathway we demonstrated here is very simple and very common. It involves the L-amino acid oxidase (LAO1) enzyme, which produces auxin through the use of tryptophan" explains Professor Aurora Galván.
The algae produces the hormone in its periplasmic space, a kind of permeable membrane 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.
Auxina teams up with bacteria and bolsters agricultural production
The team has also looked at the effects of auxin production for algae and how the hormone helps it communicate with bacteria of the genus Methylobacterium to generate beneficial interactions.
"We see that the accumulations of auxin is bad because it slows growth. At low concentrations, it actually improves the growth of the algae, but when it accumulates, it hinders it," says researcher Victoria Calatrava. To overcome these negative effects, Methylobacterium comes into play.
"The bacterium degrades the auxin by lowering the hormone levels, helping Chlamydomonas to continue growing while the bacterium obtains food from the auxin," Calatrava says. Thus, auxin functions as a mediator in that mutualistic relationship in which algae and bacteria help each other. Also, interestingly, these bacteria can feed on auxin only in the presence of the algae, which reinforces the importance of that cooperative mode.
How does this apply to the field? Pointing to the importance of auxin for plants, the researcher stressed that "both algae and bacteria live in crop fields and are part of the microbiota of plants, so their production and regulation of auxin could serve to improve agricultural production, boosting both their growth and their tolerance to stresses like drought."
Thus, once the pathway of auxin production by algae and its role in the creation of beneficial mutualisms with bacteria is understood, the team seeks to understand the role of algae in the microbiota of plants and, more specifically, the algae-bacteria-plant interaction, to evaluate its potential in the development of biostimulants that might benefit sustainable and environmentally friendly agricultural production
Reference
Calatrava V, Hom EFY, Guan Q, Llamas A, Fernández E, Galván A. Genetic evidence for algal auxin production in Chlamydomonas and its role in algal-bacterial mutualism. iScience. 2023 Dec 16;27(1):108762. doi: 10.1016/j.isci.2023.108762