The zoospores of the thraustochytrid Aurantiochytrium limacinum: Transcriptional reprogramming and lipid metabolism associated to their specific functions.

Younès Dellero,Riccardo Aiese Cigliano,Martin Schuler,Alberto Amato,Christian Morabito,Eric Maréchal,Caroline Bournaud,Fabrice Rébeillé,Cécile Maës

doi:10.1111/1462-2920.14978

Abstract

Aurantiochytrium limacinum (Thraustochytriaceae, class Labyrinthulomycetes) is a marine Stramenopile and a pioneering mangrove decomposer. Its life cycle involves a non-motile stage and zoospore production. We observed that the composition of the medium, the presence of amino acids in particular, affects the release of zoospores. Two opposite conditions were defined, one with a cell population mainly composed of zoospores and another one with almost only non-motile cells. In silico allelic frequency analysis and flow cytometry suggest that zoospores and non-motile cells share the same ploidy level and are diploid. Through an RNA-seq approach, the transcriptional reprogramming accompanying the formation of zoospores was investigated, with a particular focus on their lipid metabolism. Based on a differential expression analysis, zoospores are characterized by high motility, very active signal transduction, an arrest of the cell division, a low amino acid metabolism and low glycolysis. Focusing on lipid metabolism, genes involved in lipase activities and peroxisomal β-oxidation are upregulated. qRT-PCR of selected lipid genes and lipid analyses during the life span of zoospores confirmed these observations. These results highlight the importance of the lipid dynamics in zoospores and show the metabolic processes required to use these energy-dense molecules as fuel for zoospore survival during their quest of new territories.

Highlights

Mangrove forest environments sustain a composite ecosystem (Isa et al, 2017), with a food web primed by decomposers (Demopoulos et al, 2007)
Zoospore release As previously shown (Dellero et al, 2018a), in a rich medium (R) containing glucose and yeast extract (YE) less than 3 % zoospores were observed at best (D1), whereas in a poor medium (P), in which the glucose and yeast extract 95 (YE) concentrations were reduced to 1/40 (Supplementary Table 1), zoospores represented the main cell type (Table 1)
In order to discriminate whether amino acids hamper zoosporulation, nitrate was removed from R2 and replaced by a cocktail of amino acids in concentrations that mimic YE (R3 medium, Supplementary Table 1)

Summary

20 Abstract

Aurantiochytrium limacinum (Thraustochytriaceae, class Labyrinthulomycetes) is a marine Stramenopile and a pioneering mangrove decomposer. Its life cycle involves a non-motile stage and zoospore production. We observed that the composition of the medium, the presence of amino acids in particular, affects the release of zoospores. Based on a differential expression analysis, zoospores are characterized by high motility, very active signal transduction, an arrest of the cell division, a low amino acid metabolism and low glycolysis. QRT-PCR of selected lipid genes and lipid analyses during the life span of zoospores confirmed our observations. These results highlight the importance of the lipid dynamics in zoospores and show the metabolic processes required to use these energy-dense molecules as fuel for zoospore survival during their quest of new territories. These results highlight the importance of the lipid dynamics in zoospores and show the metabolic processes required to use these energy-dense molecules as fuel for zoospore survival during their quest of new territories. Key words: Fatty acids; GPCR pathway; Lipid metabolism; PUFA synthase; RNA-sequencing; Signal transduction; Thraustochytrids; Zoospores; ω3-docosahexaenoic acid (DHA)

Introduction

92 Results

Discussion

524 Acknowledgments