Characterization of an actin gene family in <i>Palmaria palmata</i> and Porphyra purpurea (Rhodophyta)

The actin gene family was investigated in Palmaria palmata and Porphyra purpurea, two members of the Rhodoplantae. Respectively four and two partial actin gene sequences were isolated from P. purpurea and P. palmata by PCR using actin primers deduced from the conserved regions of many classes of organisms. In P. purpurea, the partial actin gene puract1, puract2 and puract3 were shown to code for proteins whereas puract4 is a pseudogene. This result confirms the presence of several actin genes already suspected in the genus Porphyra. In P. palmata, palmact1 presents a greater identity with actin sequences from other red algae than palmact2, the second gene characterized in this species. Sequencing of the gene palmact1 revealed the existence of an intron in the coding region. To our knowledge this is the first time that two actin encoding genes have been observed in a member of the Florideophyceae. The two genes were both expressed in tetrasporophytic fronds, which raises the question as to their function. We discuss the alternative possibilities that these two genes may possess distinct roles in the cell, or fulfill similar functions in cellular mechanisms. The presence of an actin multigenic family was further demonstrated in four additional species of Rhodophyta suggesting that actin multigenic families are a relatively common feature in red algae. Phylogenetic analyses strongly support the occurrence of several independent duplication events of actin genes in the Rhodophyta.