Phylogenetic analysis of GRAS proteins from moss, lycophyte and vascular plant lineages reveals that GRAS genes arose and underwent substantial diversification in the ancestral lineage common to bryophytes and vascular plants.

GRAS genes are a large family of streptophyte specific transcription factors that function in a diverse set of physiological and developmental processes. GRAS proteins of the HAIRY MERISTEM (HAM) sub-family are required for maintenance of shoot and root indeterminacy. The transcriptional targets of HAM proteins and the signaling inputs regulating HAM activity are completely unknown. Understanding the relationship of HAM proteins to other members of the GRAS family may inform hypotheses relating to cellular level HAM functions. I here report a phylogenetic analysis of GRAS proteins employing the complete set of known and probable GRAS proteins from the sequenced genomes of the flowering plants Arabidopsis and Rice, the lycophyte Selaginella moellendorffii, and the bryophyte Physcomitrella patens. HAM proteins are most closely related to DELLA proteins, key components of gibberellin perception. However, GRAS proteins diversified into a minimum of twelve discreet monophyletic lineages, including the HAM and DELLA subfamilies, prior to divergence of the moss and flowering plant lineages. Substantial diversification of GRAS proteins at so early a point in land plant evolution suggests that relative relatedness sequence homology among GRAS proteins sub-families may not substantially reflect shared protein function.