New grass phylogeny resolves deep evolutionary relationships and discovers C4 origins.

GRASS PHYLOGENY WORKING GROUP II: ALISCIONI, S., BELL, H.L., BESNARD, G., CHRISTIN, P.-A., COLUMBUS, J.T., DUVALL, M.R., EDWARDS, E.J., GIUSSANI, L., ET AL.

NEW PHYTOLOGIST

WILEY-BLACKWELL PUBLISHING, INC

Año: 2012 vol. 193 p. 304 - 312

0028-646X

Grasses rank among the world?s most ecologically and economically important plants. Repeated evolution of the C4 syndrome has made photosynthesis highly efficient in many grasses, inspiring intensive efforts to engineer the pathway into C3 crops. However, comparative biology has been of limited use to this endeavor, due to uncertainty in the number and placement of C4 origins. Here, we aimed to solve this problem and resolve deep relationships within the grass phylogeny, building on previous work from a decade ago. We built the most comprehensive and robust molecular phylogeny for grasses to date, expanding from 62 to 546 taxa, emphasizing PACMAD species. Our final matrix comprises ~ 6000 bp and is >90% complete. For the first time, we present strong support for relationships among all the major grass lineages. Several new C4 lineages are identified, and previously inferred origins confirmed. C3-C4 evolutionary transitions have been highly asymmetrical, with 21-24 inferred origins of the C4 pathway and only one potential reversal. Our backbone tree clarifies major outstanding systematic questions and highlights C3 and C4 sister taxa for comparative studies. Two lineages emerged as hotbeds of C4 evolution. Future work in these lineages will be instrumental in understanding the evolution of this complex trait.