Genetic evidence for algal auxin production in Chlamydomonas and its role in algal-bacterial mutualism
Victoria Calatrava,
Erik F.Y. Hom,
Qijie Guan,
Angel Llamas,
Emilio Fernández,
Aurora Galván
Affiliations
Victoria Calatrava
Departamento de Bioquímica y Biología Molecular. Campus de Rabanales y Campus Internacional de Excelencia Agroalimentario (CeiA3), Edificio Severo Ochoa, Universidad de Córdoba, 14071 Córdoba, Spain; Corresponding author
Erik F.Y. Hom
Department of Biology and Center for Biodiversity and Conservation Research, University of Mississippi, University, MS 38677-1848, USA; Corresponding author
Qijie Guan
Department of Biology and Center for Biodiversity and Conservation Research, University of Mississippi, University, MS 38677-1848, USA
Angel Llamas
Departamento de Bioquímica y Biología Molecular. Campus de Rabanales y Campus Internacional de Excelencia Agroalimentario (CeiA3), Edificio Severo Ochoa, Universidad de Córdoba, 14071 Córdoba, Spain
Emilio Fernández
Departamento de Bioquímica y Biología Molecular. Campus de Rabanales y Campus Internacional de Excelencia Agroalimentario (CeiA3), Edificio Severo Ochoa, Universidad de Córdoba, 14071 Córdoba, Spain
Aurora Galván
Departamento de Bioquímica y Biología Molecular. Campus de Rabanales y Campus Internacional de Excelencia Agroalimentario (CeiA3), Edificio Severo Ochoa, Universidad de Córdoba, 14071 Córdoba, Spain
Summary: Interactions between algae and bacteria are ubiquitous and play fundamental roles in nutrient cycling and biomass production. Recent studies have shown that the plant auxin indole acetic acid (IAA) can mediate chemical crosstalk between algae and bacteria, resembling its role in plant-bacterial associations. Here, we report a mechanism for algal extracellular IAA production from L-tryptophan mediated by the enzyme L-amino acid oxidase (LAO1) in the model Chlamydomonas reinhardtii. High levels of IAA inhibit algal cell multiplication and chlorophyll degradation, and these inhibitory effects can be relieved by the presence of the plant-growth-promoting bacterium (PGPB) Methylobacterium aquaticum, whose growth is mutualistically enhanced by the presence of the alga. These findings reveal a complex interplay of microbial auxin production and degradation by algal-bacterial consortia and draws attention to potential ecophysiological roles of terrestrial microalgae and PGPB in association with land plants.