Flower development of Phalaenopsis orchid involves functionally divergent SEPALLATA-like genes.
Bottom Line: The tepal became a leaf-like organ when PeSEP3 was silenced by virus-induced silencing, with alterations in epidermis identity and contents of anthocyanin and chlorophyll.Silencing of the E-class genes PeSEP2 and PeSEP3 resulted in the downregulation of B-class PeMADS2-6 genes, which indicates an association of PeSEP functions and B-class gene expression.These findings reveal the important roles of PeSEP in Phalaenopsis floral organ formation throughout the developmental process by the formation of various multiple protein complexes.
Affiliation: Department of Life Sciences, National Cheng Kung University, Tainan, 701, Taiwan.Show MeSH
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Mentions: To further investigate the function of Phalaenopsis SEP-like genes in flower transition, floral determinacy and organ identity, we ectopically expressed PeSEP1 and PeSEP3 using the cauliflower mosaic virus 35S promoter in Arabidopsis. Ectopic expression of PeSEP3 strongly affected the flowering time, plant architecture and floral morphological features (Fig.11). When compared with wild-type Arabidopsis (Fig.11a), 35S:PeSEP3 transgenic plants with the severe phenotype had a much smaller plant size, with early flowering, whereby the terminal flower was formed after the production of a few rosette leaves (Fig.11c). Early flowering is commonly observed when SEP genes are overexpressed in Arabidopsis (Ditta et al., 2004). However, 35S:PeSEP1 transgenic plants showed no phenotypic changes (Fig.11b). 35S:PeSEP3 transgenic plants flowered with only two emaciated rosette and cauline leaves, and three flowers were produced on the terminated inflorescence (Fig.11c). In the first two flowers, sepals and petals showed abnormal morphological features, including small size and deteriorated shape (Fig.11f). For the terminal flower, sepals showed a curly oval shape, and non-expending petals did not protrude out of the sepals (Fig.11g). The stamens with short filaments were converted to organs classified as petaloid stamens. Their shape was like stamens, but with some white petal tissue, usually near the top of the organ (Fig.11g, arrowhead). The pistil was short, accompanied by a translucent ovary wall and ovules (Fig.11g, arrow).
Affiliation: Department of Life Sciences, National Cheng Kung University, Tainan, 701, Taiwan.