Abstract: The floral morphology of Cymbidium ensifolium, a well-known orchid in China, has increasingly attracted horticultural and commercial attention. However, the molecular mechanisms that regulate flower development defects in C. ensifolium mutants are poorly understood. In this work, we examined a domesticated variety of C. ensifolium named ‘CuiYuMuDan’, or leaf-like flower mutant, which lacks typical characteristics of orchid floral organs but continues to produce sepal-to leaf-like structures along the inflorescence. We used comparative transcriptome analysis to identify 6234 genes that are differentially expressed between mutant and wild-type flowers. The majority of these differentially expressed genes are involved in membrane-building, anabolism regulation, and plant hormone signal transduction, implying that in the leaf-like mutant these processes play roles in the development of flower defects. In addition, we identified 152 differentially expressed transcription factors, including the bHLH, MYB, MIKC, and WRKY gene families. Moreover, we found 20 differentially expressed genes that are commonly involved in flower development, including MADS-box genes, CLAVATA3 (CLV3), WUSCHEL (WUS), and PERIANTHIA (PAN). Among them, floral homeotic genes were further investigated by phylogenetic analysis and expression validation, which displayed distinctive spatial expression patterns and significant changes between the wild type and the mutant. This is the first report on the C. ensifolium leaf-like flower mutant transcriptome. Our results shed light on the molecular regulation of orchid flower development, and may improve our understanding of floral patterning regulation and advance molecular breeding of Chinese orchids.

Key words: Orchid, Cymbidium ensifolium, Leaf-like flower, Transcriptome