Characterisation of complementary DNAs from the expressed sequence tag analysis of life cycle stages of Laminaria digitata (Phaeophyceae)

Laminariales (Phaeophyceae, Heterokonta) are characterised by a heteromorph ic digenetic life cycle with a filamentous, microscopic gametophyte and a h ighly evolved, macroscopic sporophyte. With the ultimate goal of comparing gene expression in each life cycle stage, complementary DNA libraries were constructed from sporophytes and gametophytes of Laminaria digitata. A set of ca. 500 expressed sequence tags (EST) was generated from each life histo ry phase, by single-run partial sequencing of randomly picked cDNA clones. Comparison of the EST deduced amino acid sequences with database protein se quences assigned a putative identity for 39% of the 412 gametophyte clones and 48% of the 493 sporophyte clones sequenced thus far. These data represe nt more than 152 different proteins now probably identified in L. digitata. Several of those newly identified proteins are of interest to our understa nding of the molecular physiology of kelps, for example their carbon-concen trating mechanisms, cell wall biosynthesis and halogen metabolism. EST anal ysis also confirmed that genes with long 3'-UTRs are widespread in Laminari ales and the study of 5'-UTRs allowed the identification of a Kozak consens us sequence, c(A/C)A(A/C)CAUGGc(G/T). Several potential developmentally reg ulated differences in gene expression are discussed.