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Molecular identification of cDNAs encoding for the Poly(A)-Binding Protein in the fern Anemia phyllitidis (L.) Sw.

Background and Purpose: Analysing the molecular events initiating and characterising some important morphogenetic steps in fern gamethophytes, we stressed on the possible role of transcriptional and translational factors in these processes. One such factor is the ubiquitous poly(A)-binding protein (PABP), which has been cloned from a wide variety of organisms, but not yet from the ancient family of Archegoniates. Material and Methods: Spores of the fern Anemia phyllitidis (L.) Sw. were grown to young gamethophytes with or without the addition of the plant hormone Gibberelic acid (GA3). mRNA was extracted for RT-PCR cloning of the Anemia PABP cDNA and the analysis of the transcriptional status of the PABP gene. cDNA sequencing and phylogenetic analysis was performed to find relationships between plant PABPs. Results: Hybridisation screening of a cDNA-library from fern Anemia phyllitidis with a probe for the poly(A)-binding protein led to the isolation of full-length clone Anpab1 and a partial clone Anpab2, resembling an isogene. Sequence analysis of Anpab1 confirmed the presence of ribonucleoprotein consensus sequences (RNP). The C-terminal part of Anpab1 contains a PAPB specific region, which distinguishes poly(A)-binding proteins from other RNA-binding proteins. Phylogenetic analysis using only this C-terminal domain reveals grouping of plant PABPs into three classes. As proven by Northern blot analysis, the PABP gene is transcribed in all developmental stages examined. Conclusions: The high degree of sequence homologies of PABPs from a member of the ancient family of Archegoniates is an additional proof of the ubiquitous meaning of the poly(A)/PABP-system. Additionally, the phylogenetic grouping of fern PABPs might implicate similar functions according to members of the same group, which show involvement in several post-transcriptional processes.

PABP; RBD; RNP; Archegoniates; gametophyt; prothallium

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