Successive Evolutionary Steps Drove Pooideae Grasses from Tropical to Temperate Regions

Angiosperm adaptations to seasonally cold climates have occurred multiple times independently. However, the observation that less than half of all angiosperm families are represented in temperate latitudes suggests internal constraints on the evolution of cold tolerance/avoidance strategies. Similar to angiosperms as a whole, grasses are primarily tropical, but one major clade, subfamily Pooideae, radiated extensively within temperate regions. It is posited that this Pooideae niche transition was facilitated by an early origin of long-term cold responsiveness around the base of the subfamily, and that a set of more ancient pathways enabled evolution of seasonal cold tolerance. To test this, we compared transcriptome-level responses of disparate Pooideae to short-/long-term cold and with those previously known in the subtropical grass rice (Ehrhartoideae).