Bioprospecting of phytohormone biosynthetic pathways in the microalgal realm

Microalgae are considered sustainable factories for high added value metabolites, with growing applications in industrial or biomedical biotechnology. Carotenoids and polyunsatured fatty acids (PUFAs) are the main targets. Vitamins or polyphenols are also of interest. Metabolites such as phytohormones have not been contemplated so far in microalgae, especially due to a notable gap of knowledge. This study aimed to explore and compare the biosynthetic pathways of phytohormones along the diverse microalgal taxa, discussing the results together with data available on the qualitative and quantitative assessment of phytohormones in microalgae. A multistep in silico analysis was carried out using a selection of core enzymes from the pathways described in the flowering plant species Arabidopsis thaliana. Results showed that the enzymatic machinery for phytohormone biosynthesis known in plants is generally present in microalgae. Phylogenetic analysis inferred conserved biosynthetic routes in microalgal divisions for abscisic acid, auxins, cytokinins, ethylene and jasmonates. Endosymbiotic events generating phyla such as Ochrophyta, Cryptophyta, Haptophyta or Dinophyta likely determined divergences in the biosynthesis of auxins, gibberellins, and brassinosteroids. Microalgae can be a resource for PHs production with human health benefits, together with carotenoids, polyphenols or vitamins.