Sequence diversity and conservation of the poly(A)-binding protein in plants

Abstract

Although the poly(A)-binding protein (PABP) is relatively conserved among eukaryotes, there is a surprising degree of divergence within the Arabidopsis thaliana PABP gene family which is unique for any species investigated to date. To determine whether divergent PABPs are present in another dicot species and whether members of a PABP multigene family are conserved between plant species, cDNAs encoding PABP were isolated from Nicotiana tabacum and were compared with PABP from the Arabidopsis gene family as well as other plant species. Arabidopsis PAB2 is considerably more conserved with the tobacco (a dicot) and wheat (a monocot) PABPs so far isolated reflecting the evolution of higher plants whereas Arabidopsis PAB5 has diverged significantly from these plant PABPs. Analysis of individual domains within PABP demonstrated that of the four N-terminal RNA recognition motif (RRM) domains in Arabidopsis PAB5, RRM1, RRM2, RRM4 exhibit a higher degree of conservation with other plant PABPs whereas RRM3 and particularly the C-terminal domain have diverged from the other higher plant PABPs analyzed. These data support the hypothesis that PABP underwent gene duplication during plant evolution and that individual domains within PABP have evolved at different rates.