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zygomorphic flower with four fertile stamens and a dorsal staminode [24]. There-
fore, Opithandra represents an ideal candidate for exploring a potentially novel
genetic mechanism underlying the establishment of zygomorphy with ventral sta-
men arrest in angiosperms, especially in Lamiales s.l.
Here we report that there is a correlation between OpdCYC gene expressions
and abortion of both the dorsal and ventral stamens in Opithandra, strengthened
by the negatively correlated expression of their putative direct target OpdcyclinD3
genes. The novel patterns of CYC-like gene expressions in Opithandra indicate
that ECE-CYC2 clade TCP genes are involved in the ventral stamen repression
evolved within Lamiales s. l.
Results
Sequence and Phylogenetic Analyses of OpdCYC and
OpdcyclinD3
We isolated four CYC-like genes from Opithandra dinghushanensis, named Opd-
CYC1C, OpdCYC1D, OpdCYC2A and OpdCYC2B. The full length open read-
ing frames (ORFs) of OpdCYC1C, OpdCYC1D, OpdCYC2A and OpdCYC2B
are 1017 base pair (bp), 1038 bp, 1044 bp and 993 bp, respectively. Sequence
analyses show that they share 43-48% and 45-51% identity with AmCYC at
nucleotide and amino acid levels, respectively. When comparing the TCP and R
domains, they share 90-95% identity with AmCYC at the amino acid level, sug-
gesting they are functionally related. Phylogenetic analyses show that OpdCYC
genes have a close relationship with AmCYC and AmDICH, and, along with
AmCYC and TCP1, belong to the ECE-CYC2 clade in the ECE lineage (CYC/
TB1 subfamily) of TCP gene family [12] (Figure 2A) (We have not found a mem-
ber of the ECE-CYC3 clade yet in Gesneriaceae, probably failed to amplify them
because of difficulty in designing specific primers for this clade). OpdCYC genes
are closely related to GCYC from Oreocharis among GCYC genes in Gesneri-
aceae (Figure 2B).
Two D3-type cyclin genes, designated as OpdcyclinD3a and OpdcyclinD3b,
were isolated from O. dinghushanensis with full length ORFs of 1563 bp and
1200 bp, respectively. The two D3-type cyclin genes contain a cyclin box [29] and
the putative (Rb)-binding motif (LxCxE, where x is any amino acid) which are
found both in animals [30,31] and plants [6,32,33]. Phylogenetic analyses show
that OpdcyclinD3 genes belong to cyclinD3a and cyclinD3b clade, respectively,
in the cyclinD3 lineages, in which they have close relations with AmcyclinD3a
and AmcyclinD3b from A.majus, respectively (Figure 2C).
