Embryophyte stress signaling evolved in the algal progenitors of land plants

Significance The evolution of land plants from algae is an age-old question in biology. The entire terrestrial flora stems from a grade of algae, the streptophyte algae. Recent phylogenomic studies have pinpointed the Zygnematophyceae as the modern-day streptophyte algal lineage that is most closely related to the algal land plant ancestor. Here, we provide insight into the biology of this ancestor that might have aided in its conquest of land. Specifically, we uncover the existence of stress-signaling pathways and the potential for intimate plastid-nucleus communication. Plastids act as environmental sensors in land plants; our data suggest that this feature was present in a common ancestor they shared with streptophyte algae.