The aim of this study was to profile expression of mannuronan C5‐epimerase (ManC5‐E) genes of Laminaria digitata (Huds.) J. V. Lamour. under treatment with brown alga cell wall components known to induce defense reaction in this organism. After determining that incubation in the presence of homo‐guluronates increased the accumulation of ManC5‐E transcripts, we cloned a number of partial ManC5‐E genes from nonelicited and elicited specimens. In addition to these fragments, previously identified genes from sporophyte and protoplast cDNA libraries were considered for a clustering analysis. Several groups of ManC5‐E genes were observed, including groups containing sequences specific from nonelicited and elicited sporophytes, and sequences isolated from protoplasts. Quantitative real‐time PCR experiments were then carried out using genes representative of different groups. Results of transcript accumulation during protoplast regeneration and sporophyte elicitation supported the hypothesis that specific C5‐epimerase genes are recruited under pathogen attack, enabling L. digitata to modify its cell wall in response to environmental stimuli.

In order to identify genes involved in cell wall regeneration and stress responses in red algae, expressed sequence tags (ESTs) from protoplasts (2002 ESTs) and thalli (2052 ESTs) from the seaweedChondrus crispus(Stackh.) were studied. Clustering gave 2291 non‐redundant sequences; 50% of the ESTs showed similarity (e<10−4) to known sequences. The fraction of stress‐related ESTs was five‐times higher in the protoplast library than in the thallus library. The ESTs that were statistically over‐represented in protoplasts included: glutathione S‐transferases, heat shock proteins, vanadium bromoperoxidase, and several genes of unknown function; in all 32 transcripts. Over‐represented genes in thallus included: NADH dehydrogenase, a peroxidase, and several genes of unknown function; in all 12 transcripts. In general, the ESTs from the two libraries were very different; for example, only 38% of contigs had members of both catalogues. The approach allowed the identification of numerous stress genes; including 23 different heat shock proteins and molecular chaperones, antioxidative enzymes, and several genes potentially involved in detoxification. Genes potentially involved in the construction of the cell wall or the extracellular matrix included α‐galactosidase, pullulanase, sulfohydrolase, and several sequences with von Willebrand factor type A domains with similarities to cochlin, integrin, and vitrin.

Afin d'identifier des marqueurs moleculaires de la reponse au stress et des genes impliques dans la synthese de la paroi cellulaire chez l'algue brune Laminaria digitata, 1985 EST issus de protoplastes (cellules isolees et stressees) ont ete generees. Un quart de ces EST mannuronane-C5-epimerases (ManC5), seraient impliquees dans la synthese de la paroi. La production de protoplastes entrainant la liberation d'oligoguluronates et mimant ainsi l'attaque par un pathogene, la technique d'hybridation soustractive sur des sporophytes elicites a permis d'identifier des genes plus specifiques au stress (heat shock proteins, glutathion S-transferases) ou a la defense (thioredoxine peroxydases, 6-phosphogluconate deshydrogenase, glucose 6-phosphate deshydrogenase). De plus, nous avons mesure des variations d'expression pour quatre ManC5 par PCR quantitative chez les protoplastes et des sporophytes elicites.

To characterize stress and defense‐induced genes in the brown algaLaminaria digitata(Hudson) J.V. Lamouroux, 1985 expressed sequence tags (ESTs) were generated fromL. digitataprotoplasts. Comparison of the ESTs with public databases allowed putative functions to be assigned to 45% of the sequences. Comparison with ESTs fromL. digitatasporophytes showed that protoplasts expressed more stress genes than intact thalli. Several transcripts in the stress gene class coded for proteins involved in cell protection against oxygen radicals, including thioredoxins (six ESTs), thioredoxin peroxidases (two ESTs), and glutathione‐S‐transferase (GST) (41 ESTs). The GSTs appear to be part of the sigma class, making them the first GST sigma identified in a photosynthetic organism. Other stress genes included a new type of vanadium‐dependent bromoperoxidases (vBPO) showing 71% similarity with vBPOs previously identified in the sporophytic‐thalli phase ofL. digitata. The ESTs coding for 22 different mannuronan‐C5‐epimerases were identified among the cell wall biosynthesis genes, and several ESTs showed similarity with the genome of theEctocarpus siliculosusvirus.