MOLECULAR COMPARISON OF CARBONIC-ANHYDRASE FROM FLAVERIA SPECIES DEMONSTRATING DIFFERENT PHOTOSYNTHETIC PATHWAYS

During the evolution of C-4 plants from C-3 plants, both the function and intracellular location of carbonic anhydrase (CA) have changed. To determine whether these changes are due to changes at the molecular l evel, we have studied the cDNA sequences and the expression of CA from Flaveria species demonstrating different photosynthetic pathways. In leaf extracts from F. bidentis (C-4), F. brownii (C-4-like), F lineari s (C-3-C-4) and F, pringlei (C-3), two polypeptides of M(r) 31 kDa and 35 kDa cross-reacted with anti-spinach CA antibodies. However, the re lative labelling intensities of the two polypeptides differed dependin g on the species. Northern blot analysis indicated at least two CA tra nscripts are present in each Flaveria species with sizes ranging from 1.1 to 1.6 kb. Carbonic anhydrase cDNAs from all four Flaveria species studied encode an open reading frame for a polypeptide of 35-36 kDa. The amino acid sequences deduced from all four Flaveria cDNAs share at least 70% homology with the sequences of other dicot CAs. The F. bide ntis (C-4) CA sequence was found to be the least similar of the Flaver ia proteins and, as most of the sequence dissimilarity was found in th e first third of the CA molecule, these differences may be involved in the intracellular targeting of CA. A neighbour-joining tree inferred from CA amino acid sequences showed that the Flaveria CAs cluster with other dicot CAs forming a group distinct from those of monocot CAs an d prokaryotic and Chlamydomonas periplasmic CAs.