Characterization of LBD Genes in Cymbidium ensifolium with Roles in Floral Development and Fragrance

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Abstract
LBD transcription factors are critical regulators of plant growth and development. Recent studies highlighted their significant role in the transcriptional regulation of plant growth and metabolism. Thus, identifying the CeLBD gene in Cymbidium ensifolium, a species abundant in floral scent metabolites, could provide deeper insights into its functional significance. A total of 34 LBD genes were identified in C. ensifolium. These CeLBDs fell into two major groups: Class I and Class II. The Class I group contained 30 genes, while the Class II group included only 4 genes. Among the 30 Class I genes, several genes in the Ie branch exhibited structural variations or partial deletions (CeLBD20 and CeLBD21) in the coiled-coil motif (LX6LX3LX6L). These changes may contribute to the difficulty in root hair formation in C. ensifolium. The variations may prevent normal transcription, leading to low or absent expression, which may explain the fleshy and corona-like root system of C. ensifolium without prominent lateral roots. The expansion for CeLBDs was largely due to special WGD events in orchids during evolution, or by segmental duplication and tandem duplication. CeLBDs in different branches exhibit similar functions and expression characteristics. Promoter analysis enriched environmental response elements, such as AP2/ERF, potentially mediating the specific expression of CeLBDs under different stresses. CeLBDs were predicted to interact with multiple transcription factors or ribosomal proteins, forming complex regulatory networks. CeLBD20 was localized in the cytoplasm, it may act as a signaling factor to activate other transcription factors. CeLBD6 in Class II was significantly up-regulated under cold, drought, and ABA treatments, suggesting its role in environmental responses. Furthermore, metabolic correlation analysis revealed that its expression was associated with the release of major aromatic compounds, such as MeJA. These findings offer valuable insights for further functional studies of CeLBD genes in C. ensifolium.
Funding Information
  • Project of National Key R & D Program (2023YFD1600504, 32101583, 2023J01283, 115-PTJH16005)
  • National Natural Science Foundation of China (2023YFD1600504, 32101583, 2023J01283, 115-PTJH16005)
  • Fujian Provincial Natural Science Foundation of China (2023YFD1600504, 32101583, 2023J01283, 115-PTJH16005)
  • Innovation and Application Engineering Technology Research Center of Ornamental Plant Germplasm Resources in Fujian Province (2023YFD1600504, 32101583, 2023J01283, 115-PTJH16005)

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