Characterization of a tissue-specific and developmentally regulated β-1,3-glucanase gene family in Prunus persica

We report here on the characterization of a peach β-1,3-glucanase (ßGlu) gene family including two newly isolated basic βGlu genes, PpGns2 and PpGns3, linked in a tandem array. The deduced mature proteins PpGNS2 and PpGNS3 share 80% amino acid sequence identity, while PpGNS2 is nearly identical to PpGNS1 (99% identity). The deduced PpGNS3 protein contains a potential N-linked glycosylation site and a tetrapeptide sequence for sorting function, whereas these sites are absent in both PpGNS1 and PpGNS2. βGlu gene expression during flowering and early fruit development is both temporally and spatially regulated. The βGlu transcript reaches a high level in opening flower buds, and then decreases to very low levels at full-bloom. The transcript levels then increase once again at petal-fall (young fruitlets). Gene-specific expression studies in peach revealed that alternate members of βGlu genes were expressed at different stages of development. The PpGns1 transcript was specifically localized in calyx and carpels of opening flower buds. The PpGns3 transcript was mainly expressed at a high level during early fruit set. The PpGns2 transcript was not detected in all tissues analyzed. Transgenic tobacco plants carrying the 5′-promoter region of each of the βGlu genes fused to the uidA reporter gene revealed that PpGns2 was transcriptionally active, and was exclusively expressed in both cotyledons and first leaves of transgenic seedlings. In spite of their highly conserved 5′-flanking regions, the regulation of PpGns1 and PpGns2 was quite distinct. Upon closer investigation of these 5′-flanking regions, significant variations associated with ACGT core-containing motifs and their flanking sequences were observed.