Molecular Cloning and Analysis of a Polyphenol Oxidase Gene (HbPPO1) from the Hevea brasiliensis Laticifer

Based on the EST sequence, a 2 102 bp cDNA was isolated from the rubber tree (Hevea brasiliensis) latex (representing the laticicfer cytoplasm) with specific primers via RACE and RT-PCR. The sequence designated as HbPPO1 contains a 1 803 bp long open reading frame (ORF), 81 bp 5′ UTR and 218 bp 3′ UTR. Sequence analysis indicated that HbPPO1 putatively encodes 600 amino acids with a theoretical molecular weight (Mw) of 67.88 kDa and isolectric point (pI) of 8.56, which was predicted to be localized to the plastid. The protein contains the conserved Tyrosinase, PPO1_DWL and PPO1_KFDV domains specific to polyphenol oxidases, and shares the similarity of 85.2%, 82.0%, 79.8% and 78.2% with its homologs in Manihot esculenta, Ricinus communis, Jatropha curcas and Populus euphratica. Expression analysis showed that, among the examined tissues such as laticifer, bark and leaf, HbPPO1 expressed relatively more in the laticifer and the expression level was significantly inhibited by ethylene.