Conserved expression of Arabidopsis thaliana poly (A) binding protein 2 (PAB2) in distinct vegetative and reproductive tissues

The poly(A) tails of eukaryotic mRNAs are complexed with poly(A) binding pr otein (PABP). The poly(A)PABP complex is central to the efficient translati on initiation and control of poly (A) tail length and is required in some p athways of mRNA decay. A large gene family encodes PABPs in Arabidopsis tha liana. In striking contrast to the floral and root specific expression of t hree previously reported Arabidopsis PABPs, we demonstrate that RNA and pro tein for one highly diverse member of this family, PAB2, are expressed in r oots, stems, leaves, flowers, pollen and siliques of Arabidopsis. However. cell-type specific analysis of a PAB2 reporter gene fusion revealed that PA B2 is spatially and temporally regulated in each organ. For example, strong expression was detected only in the stele and meristem region of roots and a dramatic decrease in expression was observed upon fertilization of ovule s. Furthermore, the PAB2-reporter construct gave a nearly identical express ion pattern in transgenic tobacco, demonstrating that PAB2 expression is un der strong selective constraint. The PAB2-reporter was also strongly expres sed in the transmittal tissues of both Arabidopsis and tobacco, raising the possibility of its involvement in the pollination-dependent poly(A) tail s hortening of transmittal tissue specific mRNAs previously reported in tobac co (Wang et al., 1996, Plant J. 9, 715-727). In view of its potential role in poly(A) tail shortening, we demonstrated the strong and distinct presenc e of PAB2 protein in transmittal tissues of Arabidopsis. The evolutionary a nd functional implications of the expression pattern of PAB2 and its possib le functional roles in post-transcriptional regulation in transmittal tissu es are discussed.