CLONING AND CHARACTERIZATION OF SER/THR PROTEIN PHOSPHATASE TRANSCRIPTS IN APPLE

Several cDNA fragments corresponding to different apple (Malus domestica [L.] Borkh) protein phosphatases were amplified using fully degenerate oligonucleotide primers corresponding to amino-acid motifs highly conserved in Ser/Thr protein phosphatases. One of them, encoding an apple homolog of PPX protein phosphatase, has been used to isolate the corresponding full-length cDNA copy (PP-Mdl) from an apple cDNA library. Other amplified fragments were found to represent two distinct but partial PP2A-type phosphatase transcripts (PP-Md2 and PP-Md3), These three cDNAs were used to detect homologous gene copies in apple genomic DNA digests, Using the same probes, significant changes in PPX-type phosphatase message levels (detected by the PP-Mdl probe) were observed during the course of apple leaf development, while modest variation in the accumulation levels of the phosphatase transcripts could be detected among different organs of an apple tree. Using the apple protein phosphatase cDNA probes, fragments of very similar or identical size were detected in genomic DNA digests from several Prunus fruit-tree species, suggesting the strong sequence conservation of these genes among different plant species.