Isolation and characterization of a maintenance DNA-methyltransferase gene from peach (Prunus persica [L.] Batsch): transcript localization in vegetative and reproductive meristems of triple buds

A cDNA coding for a DNA (cytosine-5)-methyltransferase (METase) was isolated from peach (Prunus persica [L.] Batsch) and the corresponding gene designated as PpMETI. The latter encoded a predicted polypeptide of 1564 amino acid residues and harboured all the functional domains conserved in the maintenance METases group type I. PpMETI was a single copy in the cultivar Chiripa which was used as a model in the present study. Expression analyses revealed that PpMETI transcripts were more abundant in tissues with actively proliferating cells such as apical tips, uncurled leaves, elongating herbaceous stems, and small immature fruits. Peach plants bear bud clusters (triads or triple buds), consisting of two lateral and one central bud with floral and vegetative fates, respectively. PpMETI in situ hybridization was performed in triple buds during their entire developmental cycle. High and low levels of PpMETI transcript were related to burst and quiescence of vegetative growth, respectively. Message localization distinguished lateral from central buds during the meristem switch to the floral phase. In fact, the PpMETI message was abundant in the L1 layer of protruding domes, a morphological trait marking the beginning of floral transition. The PpMETI transcript was also monitored during organ flower formation. Altogether, these data suggest a relationship between DNA replication and PpMETI gene expression.