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 protein (PABP). The poly(A)PABP complex is central to the efficient translation initiation and control of poly (A) tail length and is required in some pathways of mRNA decay. A large gene family encodes PABPs in Arabidopsis thaliana. In striking contrast to the floral and root specific expression of three previously reported Arabidopsis PABPs, we demonstrate that RNA and protein for one highly diverse member of this family, PAB2, are expressed in roots, stems, leaves, flowers, pollen and siliques of Arabidopsis. However. cell-type specific analysis of a PAB2 reporter gene fusion revealed that PAB2 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 ovules. Furthermore, the PAB2-reporter construct gave a nearly identical expression pattern in transgenic tobacco, demonstrating that PAB2 expression is under strong selective constraint. The PAB2-reporter was also strongly expressed in the transmittal tissues of both Arabidopsis and tobacco, raising the possibility of its involvement in the pollination-dependent poly(A) tail shortening of transmittal tissue specific mRNAs previously reported in tobacco (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 presence of PAB2 protein in transmittal tissues of Arabidopsis. The evolutionary and functional implications of the expression pattern of PAB2 and its possible functional roles in post-transcriptional regulation in transmittal tissues are discussed.