Genome-Wide Identification and Characterization of the D-Type Cyclin Gene Family Suggests Its Potential Involvement in Zigzag Stem Formation in Tea Plant (Camellia sinensis)

Zigzag-shaped stems are a distinctive architectural trait in tea plants (Camellia sinensis), but their underlying molecular mechanisms remain poorly understood. D-type cyclins (CYCDs) regulate cell-cycle progression and proliferation, yet their roles in tea plant architecture remain unexplored. Here, we compared the zigzag-stemmed cultivar Lianyuanqiqu with the upright-stemmed cultivar Zhuyeqi using phenotypic, anatomical, lignin, and transcriptomic analyses and characterized the CsCYCD gene family genome-wide. Lianyuanqiqu exhibited locally shortened first internodes, curled leaves, and altered tissue organization, whereas lignin content did not differ significantly between cultivars. Transcriptome analysis identified 4786 differentially expressed genes (DEGs), significantly enriched in plant hormone signal transduction. Genome-wide analysis identified 22 CsCYCD genes belonging to six subgroups, with conserved gene structures and promoter cis-regulatory elements associated with hormone responses, growth, and cell cycle regulation. Expression profiling revealed that most differentially expressed CsCYCD genes, particularly members of the CsCYCD3 subgroup, were downregulated in zigzag stems, whereas CsCYCD1;2 was significantly upregulated. These findings provide the first genome-wide characterization of the CsCYCD gene family in tea plants and suggest its potential involvement in zigzag stem formation, offering insights into the molecular regulation of tea plant architecture.