A pollen-, ovule-, and early embryo-specific poly(A) binding protein from Arabidopsis complements essential functions in yeast.

Poly(A) tails of eukaryotic mRNAs serve as targets for regulatory proteins affecting mRNA stability and translation. Differential mRNA polyadenylation and deadenylation during gametogenesis and early development are now widely recognized as mechanisms of translational regulation in animals, but they have not been observed in plants. Here, we report that the expression of the PAB5 gene encoding one of the poly(A) binding proteins (PABPs) in Arabidopsis is restricted to pollen and ovule development and early embryogenesis. Furthermore, PAB5 is capable of rescuing a PABP-deficient yeast strain by partially restoring both poly(A) shortening and translational initiation functions of PABP. However, PAB5 did not restore the linkage of deadenylation and decapping, thus demonstrating that this function of PABP is not essential for viability. Also, like endogenous PABP, PAB5 expressed in yeast demonstrated genetic interaction with a recently characterized yeast protein SIS1, which is also involved in translational initiation. We propose that PAB5 encodes a post-transcriptional regulatory factor acting through molecular mechanisms similar to those reported for yeast PABP. This factor may have evolved further to post-transcriptionally regulate plant sexual reproduction and early development.