A POLLEN-SPECIFIC, OVULE-SPECIFIC, 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 prot eins affecting mRNA stability and translation, Differential mRNA polya denylation and deadenylation during gametogenesis and early developmen t 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) bind ing proteins (PABPs) in Arabidopsis is restricted to pollen and ovule development and early embryogenesis. Furthermore, PAB5 is capable of r escuing 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, thu s demonstrating that this function of PABP is not essential for viabil ity, 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 PA B5 encodes a post-transcriptional regulatory factor acting through mol ecular mechanisms similar to those reported for yeast PABP, This facto r may have evolved further to post-transcriptionally regulate plant se xual reproduction and early development.