Abstract
The molecular basis of orchid flower development is accomplished through a specific regulatory program in which the class B MADS-box AP3/DEF genes play a central role. In particular, the differential expression of four class B AP3/DEF genes is responsible for specification of organ identities in the orchid perianth. Other MADS-box genes (AGL6 and SEP-like) enrich the molecular program underpinning the orchid perianth development, resulting in the expansion of the original “orchid code” in an even more complex gene regulatory network. To identify candidates that could interact with the AP3/DEF genes in orchids, we conducted an in silico differential expression analysis in wild-type and peloric Phalaenopsis. The results suggest that a YABBY DL-like gene could be involved in the molecular program leading to the development of the orchid perianth, particularly the labellum. Two YABBY DL/CRC homologs are present in the genome of Phalaenopsis equestris, PeDL1 and PeDL2, and both express two alternative isoforms. Quantitative real-time PCR analyses revealed that both genes are expressed in column and ovary. In addition, PeDL2 is more strongly expressed the labellum than in the other tepals of wild-type flowers. This pattern is similar to that of the AP3/DEF genes PeMADS3/4 and opposite to that of PeMADS2/5. In peloric mutant Phalaenopsis, where labellum-like structures substitute the lateral inner tepals, PeDL2 is expressed at similar levels of the PeMADS2-5 genes, suggesting the involvement of PeDL2 in the development of the labellum, together with the PeMADS2-PeMADS5 genes. Although the yeast two-hybrid analysis did not reveal the ability of PeDL2 to bind the PeMADS2-PeMADS5 proteins directly, the existence of regulatory interactions is suggested by the presence of CArG-boxes and other MADS-box transcription factor binding sites within the putative promoter of the orchid DL2 gene.
Highlights
We identified transcripts that are possibly associated with labellum development, encoding DROOPING LEAF-like proteins (DL-like) and the class B MADS-domain protein PeMADS2 (Supplementary Figure S1c)
The genetic pathway that drives the correct formation of the floral organs and the establishment of floral symmetry has been studied in detail in model species, where some transcription factor families play a relevant role, mainly
The morphology of the flower organs and the establishment of bilateral floral symmetry have been widely studied, resulting in orchid-specific regulatory models where the coordinated action of MADS-box genes explains the formation of the orchid outer, lateral inner tepals, and labellum [13,14,15,16,17,18,19]
Summary
The Orchidaceae is one of the widely distributed and most diversified families of angiosperms Their evolutionary success is possibly due to sundry causes such as epiphytism, extraordinary adaptive capacities to different habitats, highly specialized pollination strategies, and diversified flower morphology [1,2,3]. There are three outer tepals in the first floral whorl; in the second whorl, the three tepals are distinguished into two lateral inner tepals and a median inner tepal called lip or labellum. This organ often has a peculiar morphology and bears distinct
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
