Impact of cadmium chloride stress on volatile compounds and expression profiling of CsHMA genes in Camellia sinensis cv. Fenghuang Dancong.

Camellia sinensis cv. Fenghuang Dancong is a Chinese oolong tea famous for its aroma diversity. Cadmium chloride (CdCl2), a toxic heavy metal, impairs plant growth and threatens food safety. Whether the metabolism of volatile compounds is affected by cadmium chloride and the related molecular mechanisms in tea plants remains unknown. In this study, a total of eleven CsHMAs genes were identified in tea plant genome and the gene structure, cis-elements, motifs, protein structure and physicochemical properties were analyzed. The results showed that the total volatile compounds decreased, followed by an increase in CdCl2 concentration. 47 volatile compounds in control group (0 mg kg-1) were detected in Fenghuang Dancong tea, while upon the application of CdCl2 at 10, 20 and 30 mg kg-1, 39, 37 and 32 volatile compounds were found. In particular, 30 mg kg-1 CdCl2 treatment significantly induced higher production of 1-heptadecene; pristane; phytane; trans-β-ionone; 1-nonadecane; and di-s-butyl phthalate, and reduced the amount of linalool and methyl salicylate. Volatile compounds profiling showed CdCl2 induced concentration-dependent reduction in total volatiles (47 compounds in controls vs. 32 compounds at 30 mg kg-1). The CsHMA2/3/5/8 exhibited pronounced upregulation in leaves, whereas CsHMA3/6 were root-predominant. Cs-HMA genes in Fenghuang Dancong tea shows strong links to various volatile compounds. Their expression under CdCl2stress suggests a role in shaping volatile profiles in different tissues. The results establish a foundation for further research on heavy metal tolerance mechanisms and aroma regulation in tea plants.