From spore to gametophyte: Investigating morphological dynamics of hyaline cells and corresponding gene expression patterns in Sphagnum

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BACKGROUND: Peatlands play a vital role in mitigating climate change and maintaining global ecological balance. At the core of these ecosystems are Sphagnum mosses, which rely on their hyaline cells-specialized structures with exceptional water retention capacity-to stabilize wetland hydrology and support long-term ecosystem function. Despite their ecological importance, the molecular mechanisms underlying the development of these unique water retention cells remain poorly understood. This study focuses on S. capillifolium, examining morphological traits and gene expression dynamics across four developmental stages to uncover how gene regulation contributes to hyaline cell formation. RESULTS: During the transition from spore germination to mature gametophytes, significant morphological changes occur in the cell walls of hyaline cells, particularly their increased volume, which distinguishes them from chlorophyllous cells. Transcriptomic analyses revealed marked changes in gene expression related to the cell wall, apoplast, and extracellular regions during hyaline cell formation. Notably, genes associated with cell wall remodeling, such as EXO70, PME, and XTH genes, were significantly involved. Phylogenetic analysis uncovered evolutionary divergence in these genes, highlighting the unique evolutionary position of Sphagnum compared to vascular plants, forming an independent branch. Further protein structure analysis revealed distinct differences in the ligand-binding sites and hydrogen bond formation of EXO70, PME, and XTH proteins compared to vascular plants, which may account for the functional changes observed. CONCLUSION: This study reveals the gene expression patterns underlying hyaline cell development in Sphagnum capillifolium, with a focus on key genes involved in cell wall remodeling. The findings highlight significant evolutionary differences between Sphagnum and vascular plants, particularly regarding the unique functional and structural characteristics of EXO70, PME, and XTH genes. These insights provide a new perspective on the molecular mechanisms behind hyaline cell formation in Sphagnum, further enhancing our understanding of its role in regulating wetland hydrological environments.

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