Identification and Functional Analysis of Two Alcohol Dehydrogenase Genes Involved in Catalyzing the Reduction of (<i>Z</i>)-3-Hexenal into (<i>Z</i>)-3-Hexenol in Tea Plants (<i>Camellia sinensis</i>)

Abstract

Alcohol dehydrogenase (ADH) is a vital enzyme in the biosynthesis pathway of six-carbon volatiles in plants. However, little is known about its functions in tea plants. Here, we identified two <i>ADH</i> genes (<i>CsADH1</i> and <i>CsADH2</i>). An <i>in vitro</i> protein expression assay showed that both CsADH1 and CsADH2 proteins can catalyze the reduction of (<i>Z</i>)-3-hexenal into (<i>Z</i>)-3-hexenol. Subcellular localization revealed that both CsADH1 and CsADH2 proteins were predominantly localized in the nucleus and cytosol. <i>CsADH1</i> had high transcripts in young stems in autumn, while <i>CsADH2</i> showed extremely high expression levels in stems and roots. The expression of <i>CsADH2</i> was mainly downregulated under ABA treatment, while <i>CsADH1</i> and <i>CsADH2</i> transcripts were significantly lower under MeJA treatment at 12 and 24 h. Under cold treatment, <i>CsADH1</i> transcripts first decreased and then increased, while <i>CsADH2</i> demonstrated an almost opposite expression pattern. Notably, <i>CsADH2</i> was significantly upregulated under simulated <i>Ectropis obliqua</i> invasion. Gene suppression by antisense oligonucleotides (AsODNs) demonstrated that AsODN_<i>ADH2</i> treatment significantly reduced <i>CsADH2</i> transcripts and the abundance of (<i>Z</i>)-3-hexenol products. The results indicate that the two <i>CsADH</i> genes may play an important role in response to (a)biotic stresses and in the process of (<i>Z</i>)-3-hexenol biosynthesis.