Expression of Cinnamyl Alcohol Dehydrogenase Gene in Response to Stresses and Phytohormones in Rehmannia glutinosa

Cinnamyl alcohol dehydrogenase (CAD) catalyzes the reduction of hydroxycinnamyl aldehydes to the corresponding alcohols in the presence of NADPH. The objective of this study was to isolate CAD cDNA and characterize the expression of CAD gene to understand regulation of the first step of lignin biosynthesis in R. glutinosa. A full-length putative CAD clone was isolated from the leaf cDNA library of R. glutinosa using an expressed sequence tag clone as a probe. The clone was 1242 bp in length, and contained an open reading frame (ORF) and 5’- and 3’-non-coding regions. The ORF encodes a polypeptide of 323 amino acid residues with a calculated molecular mass of 35,640 D. The deduced amino acid sequence of the clone showed the highest sequence similarity of 73% with apple CAD and the clone was designated as RgCAD1. The two to three major bands with the four to five minor ones on the Southern blots indicate that RgCAD1 is a member of a small multi-gene family. RgCAD1 mRNA was expressed in the leaf, flower and root, and the levels of expression were higher in the leaf and flower than in the root. The expression of RgCAD1 mRNA was reduced by paraquat and ethylene but increased by UV and jasmonic acid. The levels of CAD activity correlated differently with those of RgCAD1 mRNA in response to the stresses and hormones, indicating that the regulation of RgCAD1 expression is controlled at the transcription and translation levels. The RgCAD1 sequence and information of its regulation could be valuable in investigating the lignin biosynthesis and the possible role of the phenylpropanoid intermediates in the paraquat tolerance of R. glutinosa.