Can drought tolerance be a preadaptation to frost tolerance? : evolution of responses to drought and sudden frost within the grass subfamily Pooideae

Abstract

The grass family (Poaceae) is one of the most economical and ecological important plant family on earth. The largest of the Poaceae grass subfamilies is Pooideae. This subfamily contains many of our crop and forage grasses and it dominates the grass flora in the temperate and arctic regions. Many studies indicate that Pooideae spread from the Tropics to the temperate zone due to acquisition of frost tolerance. However, little is known about what could be the preadaptation that led to evolution of frost tolerance. Since drought responses resembles frost responses in plants, drought tolerance is a good candidate as a precursor to frost tolerance. This study asks whether drought tolerance could be a preadaptation to frost. Plants from a phylogenetically diverse set of Pooideae species were subjected to drought and sudden frost separately, and then the evolutionary history of drought and sudden frost tolerance were reconstructed by ancestral state reconstruction. The results suggest that drought tolerance is not a preadaptation to sudden frost tolerance within the subfamily Pooideae because freezing resistance is determined by phylogenetic history, but drought resistance is not. The phylogenetic signal was stronger for frost tolerance compared to the weak phylogenetic signal from drought tolerance. Further, the core Pooideae has a higher sudden frost tolerance but a lower drought tolerance compared to the early diverging linages of Pooideae. These findings suggest that drought tolerance was not a significant precursor for development of frost tolerance within Pooideae.