Fig. 1

Phylogenetic tree and conserved domains of PPOs in N. tabacum and other plant species. (a) Phylogenetic tree of NtPPOs and other PPOs in different plant species. PPOs are divided into four groups (I, II, III, IV). NtPPO members are marked with an orange circle. Red branches indicate the pairs of paralogous PPOs. PPO sequences obtained from other plant species genomes are as follows: Fugi apple pMD-PPO2, Solanum lycopersicum PPO A/A’, PPOB, PPOC, PPOD, PPOE, PPOF, apple pAPO5, Lycopersicon esculentum LePPO, Solanum tuberosum StPPO, Vicia faba VfPPO, Vitis vinifera VvPPO, Prunus armeniaca PaPPO, Populus trichocarpa PtPPO. Ntom, Nicotiana tomentosoformis L.; Nsyl, Nicotiana sylvestris L. (b) Putative transit peptide and function domain analysis by multiple sequence alignment. Gaps were introduced to achieve maximum homology among the sequences. The hydroxy A.A.-rich, Region I (‘n-region’) and thylakoid transfer domains are underlined with red lines, respectively. Putative cleavage sites are marked by a red box. His-rich copper binding domains CuA, CuB are underlined with red lines. His residues predicted to be copper-binding sites are marked by red star. KFDV domain is marked with black squares. (c) Conserved domain analysis. T, tyrosinase domain; D, PPO1_DWL domain; K, PPO1_KFDV domain