Abstract: Based on the relative conservation of plant homologous genes, a full full-length citrus homologue of APETALA2 was bioinformatically cloned by search of citrus EST database via Arabidopsis thaliana corresponding sequence. Accordingly, the 5'- and 3'-end sequences were obtained from cDNA of opening flower of Poncirus trifoliata (L.) Raf. by RACE with two gene-specific primers designed on the basis of the citrus sequence. The 1,980 bp complete cDNA, designated as Pt-AP2, contained an open reading frame (ORF) of 1,539 nucleotides and 289 bp of 5' -untranslated region (UTR) and a 152 bp 3'-UTR. The sequence has been deposited in GenBank database with the accession number of EU883665. The deduced amino acid sequence of Pt-AP2 (512 residues) showed 59.1%, 59.7%, 63.8% identity with those of Malus domestica, Arabidopsis thaliana, Petunia hybrida, respectively. Pt-AP2 amino acid sequence contained a putative nuclear localization signal sequence (KKSR) and two highly conserved AP2 domains. The semi-quantitative RT-PCR and SYBR Green I Real-time qRT-PCR were employed to analyze the expression of Pt-AP2 in different organs, revealing similar expression profiles in leave, stem, root, flower, fruit, in which the flower and fruit exhibited the highest and the lowest expression, respectively.

Key words: Citrus, Poncirus trifoliata, flower, gene, expression