The phylogeny of glyceraldehyde-3-phosphate dehydrogenase indicates lateral gene transfer from cryptomonads to dinoflagellates

Sequence analysis of two nuclear-encoded glyceraldehyde-3-phosphate dehydro genase (GAPDH) genes isolated from the dinoflagellate Gonyaulax polyedra di stinguishes them as cytosolic and chloroplastic forms of the enzyme. Distan ce analysis of the cytosolic sequence shows the Gonyaulax gene branching ea rly within the cytosolic clade, consistent with other analyses. However, th e plastid sequence forms a monophyletic group with the plastid isoforms of cryptomonads, within an otherwise cytosolic clade, distinct from all other plas tid GAPDHs. This is attributed to lateral gene transfer from an ancest ral cryptomonad to a dinoflagellate, providing the first example of genetic exchange accompanying symbiotic associations between the two, which are co mmon in present day cells.