Comparative transcriptome analysis of Discosporangium mesarthrocarpum (Phaeophyceae), Schizocladia ischiensis (Schizocladiophyceae), and Phaeothamnion confervicola (Phaeothamniophyceae), with special reference to cell wall-related genes

Abstract

Within the stramenopile lineage, only brown algae (Phaeophyceae) have evolved complex multicellularity, although some other members of the lineage (e.g., Schizocladia in Schizocladiophyceae; Phaeothamnion in Phaeothamniophyceae) also develop simple multicellular thalli. The development of an adherent extracellular matrix (ECM) is considered to be one of the key steps in the evolution of multicellularity, because ECM is involved in adhesion of cells to each other and in cell–cell communication essential for developmental, reproductive, and sophisticated defense systems. Because there are no unicellular organisms within brown algae, we considered that comparison of other stramenopile taxa closely related to brown algae and having multicellular thalli could yield clues to elucidate the evolution of multicellularity in brown algae. In this study, we investigated transcriptomes involved in cell wall polysaccharide metabolism of three stramenopile species, Discosporangium mesarthrocarpum, which is suggested to be one of the most basal taxa within Phaeophyceae, S. ischiensis, and P. confervicola. We employed 454-FLX high-throughput pyrosequencing to generate expressed sequence tag (EST) databases for these species, and performed comparative analyses between these databases and the genome sequence of the brown alga Ectocarpus siliculosus. Results indicate that cell wall polysaccharide metabolism pathways of D. mesarthrocarpum are similar to E. siliculosus, whereas those of S. ischiensis and P. confervicola are significantly different from E. siliculosus, suggesting that the components of the cell wall in S. ischiensis and P. confervicola are likely to be different from those of E. siliculosus.