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repressing stamen development, OpdCYC2A expression restricted to the dorsal
stamen and OpdCYC1C expression later concentrated in the dorsal and ventral
stamens in the third whorl might be related to abortion of the dorsal and ventral
stamens in Opithandra. In fact, the successive sections from the same individual
flower indicate that correlative with OpdCYC gene strong expression, the early
primordial growth have already been retarded in the dorsal and ventral stamin-
odes in comparison with that in the lateral stamens.
Evidence shows that CYC functions to repress stamen development in the
third whorl through its negative effect on expression of D3-type cyclin genes, in-
cluding cyclinD3b, which usually play an important role in locally regulating cell
proliferation in floral development [3,6,36]. The negative effects on cell cycle pro-
gression have been reported from other TCP genes, such as IaTCP1 from Iberis
(Brassicaceae), TCP2 and TCP4 from Arabidopsis, and CIN from Antirrhinum
[16,37,38]. We, therefore, investigated the expression pattern of OpdcyclinD3a
and D3b to test for further correlation between CYC expression and stamen abor-
tion through cell-cycle regulation, especially the ventral stamens. In strengthening
the above suggestion, OpdcyclinD3 genes have expression patterns in floral tis-
sues negatively correlated with those of OpdCYC genes and stamen abortion in
Opithandra. Both Opdcyclin D3a and D3b transcripts are not detected, or weak-
ly detected (i.e. dorsal), in the dorsal and ventral staminodes where both OpdCY-
C2A and OpdCYC1C or OpdCYC1C are strongly and continuously expressed
throughout floral development, while their transcripts are much more concen-
trated in the lateral stamens where there is only a weak expression of OpdCYC1C
in early stages. These factors indicate that OpdCYC gene activities may suppress
the development of the dorsal and ventral stamens through negatively regulating
OpdcyclinD3 genes (Figure 5). Our recent findings of consensus-binding sites of
the TCP transcription factor in the 5' upstream regions of OpdcyclinD3 homo-
logues, i.e. ChcyclinD3a and D3b in Chirita heterotricha, further support the
direct regulatory relation between CYC-like and cyclinD3 genes in Gesneriaceae
(Yang, Xia and Wang, Yin-Zheng, unpublished).
It seemingly remains a question whether OpdCYC activity is related to the lat-
eral stamen development or not because OpdCYC1C has a weak expression in the
early developing lateral stamens but has no obvious effect on their growth. The
evidence that CYC-like genes regulate lateral stamen development comes from
both functional analyses in Antirrhinum and expression data in Mohavea and
Chirita [3,4,21,23,25]. A gradient of CYC effect along the dorsoventral axis re-
sults in abortion of the dorsal stamen and reduced size of lateral stamens in com-
parison with ventral ones in A. majus, while CYC-like gene strong and continuous
expressions in both the dorsal and lateral stamens is correlated with abortion of
both of them in Mohavea and Chirita [4,23,25,26]. The TCP1 gene is expressed
