Cellulose accumulation in the secondary cell walls is negatively correlated with the tenderness of new shoots in Camellia sinensis

Tea, which is usually made from the new shoots of tea plants (Camellia sinensis), is one of the most popular and healthy beverages. The tenderness of new shoots plays a critical role in the production of high-quality tea; however, the factors affecting the tenderness of the new shoots of tea have not been extensively studied. Here, we show that cellulose accumulation is negatively correlated with the tenderness of new shoots, including leaves and stems, by characterizing the cellulose content and visualizing cellulose in the new shoots of two cultivars ("Huangjinya" and "Yujinxiang") via toluidine blue staining. We further found that the number of cells with secondary cell walls (SCWs) and the thickness of SCWs increased with the maturity degree of stems in both cultivars. Because cellulose is the most abundant polymer in SCW, we next identified three cellulose synthase CsCesAs, CsCesA4, 7, and 8A, through homologous alignment with Arabidopsis AtCesAs. Protein sequence analysis revealed that these proteins were closely related based on the phylogenetic analysis. We finally showed that the gene expression of the three CsCesAs was positively correlated with the maturity degree and cellulose content of the new shoots. Thus, our data suggest that cellulose accumulation, especially in the SCWs, is negatively correlated with the tenderness of new shoots in tea plants.