title: The GapA/B gene duplication marks the origin of Streptophyta (charophytes and land plants).
abstract: Independent evidence from morphological, ultrastructural, biochemical, and molecular data have shown that land plants originated from charophycean green algae. However, the branching order within charophytes is still unresolved, and contradictory phylogenies about, for example,the position of the unicellular green alga Mesostigma viride are difficult to reconcile. A comparison of nuclear-encoded Calvin cycle glyceraldehyde-3-phosphate dehydrogenases (GAPDH) indicates that a crucial duplication of the GapA gene occurred early in land plant evolution. The duplicate called GapB acquired a characteristic carboxy-terminal extension (CTE) from the general regulator of the Calvin cycle CP12. This CTE is responsible for thioredoxin-dependent light/dark regulation. In this work, we established GapA, GapB, and CP12 sequences from bryophytes, all orders of charophyte as well as chlorophyte green algae, and the glaucophyte Cyanophora paradoxa. Comprehensive phylogenetic analyses of all available plastid GAPDH sequences suggest that glaucophytes and green plants are sister lineages and support a positioning of Mesostigma basal to all charophycean algae. The exclusive presence of GapB in terrestrial plants, charophytes, and Mesostigma dates the GapA/B gene duplication to the common ancestor of Streptophyta. The conspicuously high degree of GapB sequence conservation suggests an important metabolic role of the newly gained regulatory function. Because the GapB-mediated protein aggregation most likely ensures the complete blockage of the Calvin cycle at night, we propose that this mechanism is also crucial for efficient starch mobilization. This innovation may be one prerequisite for the development of storage tissues in land plants.
authors.affiliation: Institut für Genetik, Technische Universität Braunschweig, Braunschweig, Germany. j.petersen@tu-bs.de
authors.forename: Jörn
authors.initials: J
authors.lastname: Petersen
authors.forename: René
authors.initials: R
authors.lastname: Teich
authors.forename: Burkhard
authors.initials: B
authors.lastname: Becker
authors.forename: Rüdiger
authors.initials: R
authors.lastname: Cerff
authors.forename: Henner
authors.initials: H
authors.lastname: Brinkmann
mesh_terms: D000595:Amino Acid Sequence; D001499:Bayes Theorem; D044002:Bryophyta / Q000235:genetics; D044522:Characeae / Q000145:classification / Q000235:genetics*; D000460:Chlorophyta / Q000235:genetics; D000458:Cyanobacteria / Q000235:genetics; D044424:Cyanophora / Q000235:genetics; D019143:Evolution, Molecular; D020440:Gene Duplication; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D010944:Plants / Q000145:classification / Q000235:genetics*
chemical_list: D010940:Plant Proteins; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases