The Stepwise Increase in the Number of Transcription Factor Families in the Precambrian Predated the Diversification of Plants On Land.

The colonization of the land by streptophytes and their subsequent radiation is a major event in Earth history. We report a stepwise increase in the number of transcription factor (TF) families and subfamilies in Archaeplastida before the colonization of the land. The subsequent increase in TF number on land was through duplication within existing TF families and subfamilies. Almost all subfamilies of the Homeodomain (HD) and basic Helix-Loop-Helix (bHLH) had evolved before the radiation of extant land plant lineages from a common ancestor. We demonstrate that the evolution of these TF families independently followed similar trends in both plants and metazoans; almost all extant HD and bHLH subfamilies were present in the first land plants and in the last common ancestor of bilaterians. These findings reveal that the majority of innovation in plant and metazoan TF families occurred in the Precambrian before the Phanerozoic radiation of land plants and metazoans.