Biology Reference
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early in floral buds of Arabidopsis, but the mature flowers of Arabidopsis are acti-
nomorphic because they lack later effects of TCP1 [12,15]. In Iberis amara closely
related to Arabidopsis, the IaTCP1 strong dorsal-specific expression represses the
two dorsal petal growths to become much smaller than the ventral ones in size,
while IaTCP1 has only a weak expressional signal in the natural actinomorphic
variants [16]. In the tetrandrous flowers of Oreocharis that is closely related to
Opithandra in both morphology and GCYC phylogeny [24] (Figure 2B), there is
also a weak expression of CYC homologue ObCYC in the early developing lateral
stamens that are reduced in size compared with ventral ones at anthesis as in A.
majus [39]. In Bournea, another Opithandra's close relative with actinomorphic
flowers in Gesneriaceae, the CYC homologue BlCYC1 is strongly expressed in the
dorsal petal and stamen in early development and is downregulated later, which
is correlated with the floral development undergoing a morphological transition
from initial zygomorphy to actinomorphy at anthesis with five fertile stamens in
Bournea [35]. According to Cubas [1], the maintenance of CYC expression after
early floral development should be important for generating the morphological
asymmetries in the flowers. Preston and Hileman [3] also suggest that early ex-
pression of CYC-like genes may be unimportant for establishing mature flower
symmetry. The high concentration of OpdcyclinD3a and D3b transcripts in the
lateral stamens also indicates that OpdCYC1C has lost negative effects on their
expression after early floral development; therefore, the two lateral stamens are
fertile at anthesis in Opithandra (Figure 5).
Figure 5.
Diagram showing OpdCYC gene expressions correlated with the floral morphology, especially the
infertility of the two ventral stamens in Opithandra, complemented by the expression of their putative negative
target OpdcyclinD3 genes.
Notes: dorsal
staminode is in blue, lateral stamens in green and ventral staminodes in pink; the gene that is not
boxed indicates this gene is expressed in a pattern as shown by the shaded parts within the circle (shaded degrees
indicate relative levels of gene expression); the gene boxed indicates this gene is not expressed or has very little
expression signals in the floral tissues.
