Insights into the biosynthesis pathway of phenolic compounds in microalgae

Abstract

Among the most relevant bioactive molecules family, phenolic compounds (PCs) are well known in higher plants, while their knowledge in microalgae is still scarce. Microalgae represent a novel and promising source of human health benefit compounds to be involved, for instance, in nutraceutical composition. This study aims to investigate the PCs biosynthetic pathway in the microalgal realm, exploring its potential variability over the microalgal biodiversity axis. A multistep in silico analysis was carried out using a selection of core enzymes from the pathway described in land plants. This study explores their presence in ten groups of prokaryotic and eukaryotic microalgae.. Analyses were carried out taking into account a wide selection of algal protein homologs, functional annotation of conserved domains and motifs, and maximum-likelihood tree construction. Results showed that a conserved core of the pathway for PCs biosynthesis is shared horizontally in all microalgae. Conversely, the ability to synthesize some subclasses of phenolics may be restricted to only some microalgal groups (i.e., Chlorophyta) depending on featured enzymes, such as the flavanone naringenin and other related chalcone isomerase dependent compounds.

Keywords: Blue biotechnology; Flavonoids; In silico analysis; Microalgae; Polyphenols.

Graphical abstract

Fig. 1

Major routes in phenylpropanoid/flavonoid pathway: red line: lignins; blue line: gallotannins and elagitannins; dark-green line: coumarins; orange line: stillbenoids; purple line: isoflavonoids; light-green line: flavonoids (flavanols, 3-flavonols); pink line: catechins, anthocyanins. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 2

Heatmap build by normalized BLASTp scores obtained from plant entries of 29 selected core enzyme in phenylpropanoid pathway using. A subset of 47 algal taxa.

Fig. 3

PCA of normalized BLASTp scores obtained from plant entries of 29 selected core enzymes in phenylpropanoid pathway. Cyanobacteria (dots), primary endosymbiotic event (triangles) and secondary endosymbiotic event (squares) eukaryotic algae are plotted following the colour legend in Fig. 2. Tertiary endosymbiotic event alga Euglena is marked by a void circle.

Fig. 4

ML-tree for PAL enzyme. Phylogeny was obtained starting from 236 protein sequences. Thicker clades indicate node support >75%. Green, cyan and magenta boxes represent motifs retrieved by MEME analysis of algal sequences within the domain IPR001106. Algal divisions are indicated as color arches, following the legend presented in Fig. 2. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 5

ML-tree for 4CL enzyme. Phylogeny was obtained starting from 882 protein sequences. Thicker clades indicate node support >75%. Green, cyan and magenta boxes represent motifs retrieved by MEME analysis of algal sequences within the domain IPR000873. The Ser/Thr/Gly-rich trait and a conserved Pro-Lys-Gly triplet are highlighted in the red box. Algal divisions are indicated as color arches, following the legend presented in Fig. 2. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 6

ML-tree for CAD-DFR enzymes. Phylogeny was obtained starting from 722 CAD and 109 DFR protein sequences. Thicker clades indicate node support >75%. At the end of leaves, dark and light blue colors differentiate DFR and CAD sequences, respectively. Red bars and green, cyan and magenta boxes represent motifs retrieved by MEME analysis of algal sequences within the respective domains IPR002328 and IPR001509. Algal divisions are indicated as color arches, following the legend presented in Fig. 2. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 7

ML-tree for CHS enzyme. Phylogeny was obtained starting from 506 protein sequences. Thicker clades indicate node support >75%. Green, cyan and magenta boxes represent motifs retrieved by MEME analysis of algal sequences within the domains IPR011141 (inner) and IPR004655 (outer). Algal divisions are indicated as color arches, following the legend presented in Fig. 2. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)