Identification of the NAC gene family in <i>Camellia sinensis</i> and expression analysis of <i>CsNAC65</i> under shading treatment

NAC transcription factors represent a significant class of plant-specific transcription factors that regulate growth, development, and stress responses. To investigate the regulatory effects of NAC transcription factors on tea plant shading, this study identified and analyzed the NAC gene family, revealing 100 <italic>CsNAC</italic> genes distributed across 15 chromosomes. Based on phylogenetic analysis, these genes were categorized into 16 subfamilies, which identified eight pairs of tandem duplications and 37 pairs of segmental duplications. <italic>Cis</italic>-acting element analysis indicated that the promoter regions of <italic>CsNAC</italic> genes are linked to plant growth, metabolism, and environmental stress responses. The 100 <italic>CsNAC</italic> genes exhibited varying expression levels across different tissues. Additionally, we examined the effects of varying treatment durations (5, 15, and 30 d) under 80% shading on the levels of photosynthetic pigments, tea polyphenols, free amino acids, flavonoids, and catechin components (EC, ECG, EGCG, etc.) in tea leaves. The results demonstrated that shading increased tea leaves' chlorophyll and free amino acid content while decreasing tea polyphenols, flavonoids, and catechins. Furthermore, we identified 11 <italic>CsNAC</italic> genes for expression analysis under shade treatment, revealing that the expression of <italic>CsNAC65</italic> increased by 8.46 times under shading conditions. Consequently, we focused on the <italic>CsNAC65</italic> gene and conducted an in-depth analysis, including assessments of its transmembrane structure, secondary structure, tertiary structure, sequence alignment, and subcellular localization. In summary, this study enhances our understanding of the expression patterns of <italic>CsNAC</italic> genes under shading treatment and provides a foundation for further exploration of their regulatory effects on tea quality metabolites.