YABBY gene family

From Purdue Genomics Database Facility

Victor A. Albert

The primary function of the YABBY transcription factor family in angiosperms is to specify abaxial cell fates in lateral organs produced by apical and flower meristems. Homologs of YABBY gene family members can be found in many EST library sets, e.g., from developing reproductive tissues of a variety of basal angiosperms, young spruce shoot tips, and young cycad leaves. I have not found YABBY homologs in ferns or Physcomitrella, so it comes as little surprise that no family members appear to exist in Selaginella. Apparently, YABBY transcription factors are an innovation of the lateral-organed seed plant lineage.

See also: Floyd SK, Bowman JL. Distinct developmental mechanisms reflect the independent origins of leaves in vascular plants. Curr Biol. 2006 Oct 10;16(19):1911-7. PMID: 17027487

These authors present expression evidence from Class III HD-Zip genes for the non-homology of Selaginella microphylls and seed-plant megaphylls. Importantly, the fossil record suggests distinct evolutionary pathways to fern vs. seed plant megaphylls, which concurs with the absence of YABBY homologs in ferns, as noted above.

Note as well that some extinct lepidodendralean lycopod trees had lateral branching systems, which based on the absence of YABBY factors in Selaginella, may speak to the non-homology of their regulatory control vis-a-vis the lateral organs of seed plants.