Biology Reference
In-Depth Information
Zygomorphic flowers with three staminodes at the dorsal and lateral positions
or at the dorsal and ventral sides have been considered to be derived in the family
Gesneriaceae [24,40-42]. In the primitive zygomorphic taxa, such as Haberlea
and Oreocharis characteristic of tetrandrous flowers with four didynamous sta-
mens plus a dorsal staminode, and the derived actinomorphic groups (definition
see note in [35]), such as Ramonda and Bournea, there is only one single copy
of GCYC1 and GCYC2, respectively, found to date (Figure 2B) [35,39,43,44].
However, two copies of GCYC1 are frequently found in the advanced zygo-
morphic taxa, especially in the zygomorphic genera characterized by diandrous
flowers with three staminodes, such as two African genera Streptocarpus and
Saintpaulia with GCYC1A and GCYC1B [44,45] and Asian genera Didymo-
carpus, Chirita and Loxostigma with GCYC1C and GCYC1D [25,46] as well as
Opithandra herein (Figure 2B). Recent studies show that two copies of GCYC2
(GCYC2A/2B) are also found in the Asian genera with three staminodes, such as
Chirita [25] and Opithandra in this study (Figure 2B). The derived morphology
of diandrous flowers might have resulted from subsequent expression differen-
tiation after gene duplication events. In the diandrous flowers of Chirita (also
Gesneriaceae) that differs from Opithandra in abortion of both the dorsal and
lateral stamens rather than ventral stamens, ChCYC1C is strongly expressed both
in the dorsal and lateral stamens while ChCYC1D maintains strong expressions
in the dorsal floral regions, and ChCYC2A/2B have no expression signals in floral
tissues [25]. No expression of GCYC2 detected in floral tissue is frequently found
in Gesneriaceae while GCYC1 is usually conserved in dorsal-specific expression
in this family, such as Oreocharis and Bournea [35,39]. Therefore, the peculiar di-
androus flowers established in Opithandra might involved not only gained or en-
hanced expression of OpdCYC1C in ventral staminodes but also the reactivated
expression of OpdCYC2A specific to the dorsal staminode accompanied with the
downregulation of OpdCYC1D in the dorsal region in the third whorl, a more
complicated mechanism than that in another diandrous flowers of Chirita.
Phylogenetic analyses show that the CYC-like genes isolated from Opithandra
and other Gesneriaceae belong to ECE-CYC2 clade as CYC and TCP1 from An-
tirrhinum and Arabidopsis (Figure 2B) [25,35,39,45]. As outlined above, ECE-
CYC2 clade genes are characteristic of dorsal identity function which some-
times expands to lateral stamens [4,5,21,23,25,35,39]. It would be especially
interesting to know whether or how CYC-like gene activities are related to abor-
tion of the ventral stamens [3,12,20]. Even though not tested functionally, this
positive correlation between CYC-like gene expression and ventral stamen
abortion and the complement of cyclinD3 to CYC-like gene expressions sug-
gests a genetic mechanism underlying the establishment of zygomorphy with
abortion of both the dorsal and ventral stamen evolved within Lamiales s.l.
However, it has been shown for Veronica and Gratiola (also Lamiales s.l.) that
