Abstract: In this study，the HD-Zip transcription factor CsHB1 gene was cloned from‘Yinghong 9’（Camellia sinensis）tea plant，and the recombinant CsHB1 protein was expressed in Escherichia coli. The subcellular localization of CsHB1 was carried out using tobacco as an expression host. The RNAi transgenic vector of CsHB1 was constructed and transformed into‘Yinghong 9’tea callus mediated by Agrobacterium，followed by the analysis of gene expression and caffeine content on the silence CsHB1 callus. Our results showed that the cloned CsHB1 gene shared the same amino acid sequence exception 6 nucleotides difference with NCBI registered CsHB1 gene（accession No. MF033534）isolated from‘Longjing 43’tea plant. A 49 kD insoluble recombinant protein corresponding to the CsHB1 gene was obtained by prokaryotic induction. The expression protein infused with GFP as GFP-CsHB1 located in the cell nucleus and cytoplasm of tobacco. In the silence expression of CsHB1 callus，the expression of the CsHB1 gene decreased significantly，and the expression of yhNMT1，an N-methyltransferase，which catalyzes the synthesis of caffeine in tea，was also found decreased by real-time fluorescence quantitative PCR analysis. HPLC analysis showed that the content of caffeine in the transgenic callus decreased markedly. Based on these results，we suggest that the silencing of CsHB1 suppresses the expression of yhNMT1，and then reduces the accumulation of caffeine in the callus of‘Yinghong 9’.

Key words: tea, caffeine, HD-Zip transcription factor, RNA interference