Phylogenetic tree of SPSs. SPSs from Craterostigma plantagineum (8), Solanum tuberosum (2), Vicia faba (4), Beta vulgaris (5), Spinacia oleracea (10), Zea mays (30), Saccharum officinarum (GenBank accession no. AB001338), Oryza sativa (28), Citrus unshiu (11), Musa acuminata (GenBank accession no. U59489), and Synechocystis sp. strain PCC 6803 (9) were used to construct this tree. The tree was generated with the program Megalign of the DNAStar package, using the Clustal method with PAM 250 residue weight table.