Polyploidization Alters the Plant Cell Wall Composition of Dendrobium catenatum Orchids

Polyploid plants often present a variety of agriculturally advantageous traits, such as larger organs. Plant cell expansion is ultimately constrained by the cell wall, yet the impact of polyploidization on the cell wall architecture of orchids remains unexplored. Here, we employed Dendrobium catenatum (syn. D. officinale) as a model to dissect the impacts of polyploidization on phenotypic traits, cell size and cell wall composition. Compared with diploids, tetraploids of D. catenatum have larger organs underpinned by larger cells. The analysis of gene expression revealed that the differentially expressed genes (DEGs) were significantly enriched in the cell wall metabolism and DNA packaging pathways. The cell wall component lignin- and xylan-related transcripts were upregulated, whereas histone-variant genes were repressed. Compositional assays revealed that the contents of many cell wall components, such as lignin, are increased in tetraploids. Despite cell wall reinforcement, tetraploids remained colonized by the symbiotic fungus Serendipita indica, although fungal biomass was moderately reduced. Thus, polyploidization enlarges D. catenatum by reprogramming cell wall construction, while preserving the plant's ability to maintain fungal symbiosis.