KUZOFF, ROBERT K.*, JOHN L. BOWMAN, AND CHARLES S. GASSER. Sections of Molecular and Cellular Biology and Plant Biology, University of California, Davis, CA 95616. - Structural and functional diversification of the YABBY gene family across angiosperms.
Members of the YABBY gene family, recently discovered in
Arabidopsis thaliana, are crucial for the establishment of
abaxial identity in diverse organs including leaves, floral appendages
and ovules. YABBY genes encode putative transcription factors with a
zinc finger domain near the N-terminus, a central variable region, and
a YABBY domain near the C-terminus. To explore the patterns and rates
of diversification among members of the YABBY gene family across
angiosperms, we isolated several homologs from two Asterids,
Lycopersicon esculentum and Antirrhinnum majus, and a
monocot, Zea mays. Amino acid sequences of both the zinc finger
and YABBY regions from all isolated genes were easily aligned. The
central variable regions among these genes exhibited some similarities
but could not be unambiguously aligned. Phylogenetic analysis of these
genes, using the PAM-250 amino acid transition matrix, identified five
distinct molecular lineages, with high bootstrap support, that
correspond to functional categories identified in A. thaliana.
Within these lineages, the zinc finger regions, having an average
sequence dissimilarity of 18.6%, are evolving more rapidly than the
YABBY regions, which have an average sequence dissimilarity of 6.7%.
Orthologs of INNER NO OUTER, a gene required for outer
integument development in A. thaliana, have been identified in
both the Asterid and monocot lineages. Orthologs of CRABS CLAW,
a gene involved in abaxial differentiation of the carpel, have also
been identified in these lineages. In situ hybridization of
orthologs of INNER NO OUTER and CRABS CLAW in L.
esculentum indicates that they are expressed in the same tissues
as their counterparts in A. thaliana, but also exhibit expanded
expression patterns relative to A. thaliana. The pattern of
INNER NO OUTER expression in ovules of L. esculentum may
provide insights into the origin of unitegmy in the Asterids, in
particular, and the relationship between molecular and morphological
evolution, more generally.
Key words: Carpel Diversification, CRABS CLAW, Evolution of Development, INNER NO OUTER, Ovule Diversification, YABBY gene family