Genome-wide identification and functional characterization of LBD gene family in four Cymbidium species (Orchidaceae) and potential regulatory role of CsiLBD27 in floral development of Cymbidium sinense.

BACKGROUND

The Lateral Organ Boundaries Domain (LBD) gene family, encompassing plant-specific LOB domain proteins, plays essential roles in various aspects of plant growth and development, and has continuously diversified its functions across numerous species. However, studies on LBD genes in the Orchidaceae family remain limited. To our knowledge, this is the first systematic investigation of the LBD gene family in Cymbidium, a genus that exhibits remarkable species and trait diversity within the Orchidaceae.

RESULTS

In this study, we identified 122 LBD genes within the genomes of four Cymbidium species, distributed on 20 chromosomes. These genes were classified into class I (109 members, including 16 in subclass Ic/d) and class II (13 members), with protein lengths ranging from 94-477 amino acids. Promoter sequences of CymLBD genes revealed various cis-elements significant for light, hormonal, biotic, and abiotic stress responses. Transcriptomic analysis revealed tissue- and stage-specific expression of CymLBD genes in Cymbidium, and RT-qPCR and yeast one-hybrid assays indicated that CsiLBD27 may regulate floral patterning by directly binding to the CsiSEP3 promoter and activating its transcription. Under ABA treatment, the genes CsiLBD13, CsiLBD19, and CsiLBD21 displayed tissue-specific expression changes, suggesting hormone-responsive regulation. In Cymbidium ensifolium, 16 CenLBD genes were differentially expressed, while in Cymbidium mannii, 9 CmaLBD gene expression exist obvious circadian rhythm. GO and KEGG enrichment of 1074 and 399 predicted target genes, respectively, indicating a diverse range of functions for LBDs.

CONCLUSIONS

Collectively, this study provides the first comprehensive insight into the evolutionary dynamics, regulatory mechanisms, and functional roles of LBD genes in Cymbidium. These findings offer a valuable genetic resource for understanding floral and vegetative development in Orchidaceae and uncover potential novel functions of LBD genes.