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zygomorphy in Lamiales sensu lato, a major clade of predominantly zygomor-
phically flowered angiosperms. Opithandra (Gesneriaceae) is of particular in-
terests in addressing this question as it is in the base of Lamiales s.l., an early
representative of this type zygomorphy.
Results
We investigated the expression patterns of four ECE-CYC2 clade genes and
two putative target cyclinD3 genes in Opithandra using RNA in situ hybrid-
ization and RT-PCR. OpdCYC gene expressions were correlated with abor-
tion of both dorsal and ventral stamens in Opithandra, strengthened by the
negatively correlated expression of their putative target OpdcyclinD3 genes.
The complement of OpdcyclinD3 to OpdCYC expressions further indicated
that OpdCYC expressions were related to the dorsal and ventral stamen abor-
tion through negative effects on OpdcyclinD3 genes.
Conclusion
These results suggest that ECE-CYC2 clade TCP genes are not only function-
ally conserved in the dorsal stamen repression, but also involved in arresting
ventral stamens, a genetic mechanism underlying the establishment of zygo-
morphy with abortion of both the dorsal and ventral stamens evolved in an-
giosperms, especially within Lamiales s.l.
Background
One important event during the evolution of angiosperms is the emergence of
flower bilateral symmetry, i.e. zygomorphy, a key innovation associated with im-
portant adaptive radiations [1]. Several zygomorphic clades have independently
evolved successfully from actinomorphic ancestors in angiosperms, including La-
miales sensu lato that includes a major genetic model organism snapdragon (An-
tirrhinum majus) [2,3].
In A.majus, CYCLOIDEA (CYC) and DICHOTOMA (DICH) are essential
for the development of dorsoventral asymmetry in flowers due to their dorsal
identity function, i.e. controlling the fate of the dorsal floral organs in the second
and third whorls [4,5]. CYC promotes cell expansion in the dorsal petals, while
it arrests the growth of the dorsal stamen to become a staminode [4,5]. Mean-
while, DICH activity affects the internal asymmetry of the dorsal petals [4,5].
The ability of CYC to arrest the dorsal stamen depends on its negative effect on
expression of cell-cycle genes, such as cyclin D3b [3,6]. CYC and DICH encode
proteins within the ECE-CYC2 clade (ECE lineage, CYC/TB1 subfamily) in the
TCP family of transcription factors with TCP domain related to cell proliferation
