Genome-Wide Identification and Gene Expression Analysis of the LBD Transcription Factor Family in Eelgrass (Zostera marina L.)

Eelgrass (Zostera marina L.) is a typical seagrass species that plays a crucial role in marine ecosystems. Lateral organ boundaries (LOB) domain (LBD) genes, a family of plant-specific transcription factors characterized by the conserved LOB domain, are involved in the regulation of plant growth and development. However, this gene family has not yet been characterized in eelgrass. In this study, we performed a genome-wide identification, structural characterization, and expression analysis of LBD genes in Z. marina. A total of 23 ZosmaLBD genes (ZosmaLBD01 to ZosmaLBD23) were identified, which were unevenly distributed across six chromosomes. Phylogenetic analysis classified the ZosmaLBD family into two classes: Class I and Class II. Conserved motif and gene structure analyses revealed significant differences in the exon number, as well as in the count, type, and arrangement order of conserved motifs between Class I and Class II members. Promoter analysis predicted 49 types of cis-elements associated with plant growth and development, phytohormone responses, and abiotic and biotic stress responses in the promoters of ZosmaLBD genes. RNA-seq and qRT-PCR analyses showed that most ZosmaLBDs (14/23) were expressed in at least one tissue and exhibited diverse expression profiles. Notably, ZosmaLBD02, 17, and 20 in Class II were constitutively highly expressed in all tissues and were differentially expressed in most pairwise tissue comparisons, whereas ZosmaLBD01 and ZosmaLBD10 were specifically highly expressed in roots. These genes represent key candidates for further functional studies. Our findings provide a valuable foundation for understanding the potential roles of ZosmaLBDs in eelgrass growth and development.