AUTHOR=Zhang Wenheng , Steinmann Victor W., Nikolov Lachezar , Kramer Elena M., Davis Charles 

TITLE=Divergent genetic mechanisms underlie reversals to radial floral symmetry from diverse zygomorphic flowered ancestors

JOURNAL=Frontiers in Plant Science

VOLUME=4

YEAR=2013

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2013.00302

DOI=10.3389/fpls.2013.00302

ISSN=1664-462X

ABSTRACT=<p>Malpighiaceae possess flowers with a unique bilateral symmetry (zygomorphy), which is a hypothesized adaptation associated with specialization on neotropical oil bee pollinators. Gene expression of two representatives of the <italic>CYC2</italic> lineage of floral symmetry TCP genes, <italic>CYC2A</italic> and <italic>CYC2B</italic>, demarcate the adaxial (dorsal) region of the flower in the characteristic zygomorphic flowers of most Malpighiaceae. Several clades within the family, however, have independently lost their specialized oil bee pollinators and reverted to radial flowers (actinomorphy) like their ancestors. Here, we investigate <italic>CYC2</italic> expression associated with four independent reversals to actinomorphy. We demonstrate that these reversals are always associated with alteration of the highly conserved <italic>CYC2</italic> expression pattern observed in most New World (NW) Malpighiaceae. In NW <italic>Lasiocarpus</italic> and Old World (OW) <italic>Microsteria</italic>, the expression of <italic>CYC2</italic>-like genes has expanded to include the ventral region of the corolla. Thus, the pattern of gene expression in these species has become radialized, which is comparable to what has been reported in the radial flowered legume clade <italic>Cadia</italic>. In striking contrast, in NW <italic>Psychopterys</italic> and OW <italic>Sphedamnocarpus</italic>, <italic>CYC2</italic>-like expression is entirely absent or at barely detectable levels. This is more similar to the pattern of <italic>CYC2</italic> expression observed in radial flowered <italic>Arabidopsis</italic>. These results collectively indicate that, regardless of geographic distribution, reversals to similar floral phenotypes in this large tropical angiosperm clade have evolved via different genetic changes from an otherwise highly conserved developmental program.</p>