MOLECULAR-CLONING AND TISSUE-SPECIFIC EXPRESSION OF 2 GENES THAT ENCODE CAFFEIC ACID O-METHYLTRANSFERASES FROM POPULUS-KITAKAMIENSIS

Two genes (homt1 and homt2) for caffeic acid: S-adenosyl-L-methionine O-methyltransferase (OMT) were isolated from Populus kitakamiensis, Nu cleotide sequencing analysis revealed that the coding sequence of homt 1 exhibited 99% homology to the cDNA for lignin bi-specific OMT from q uaking aspen. The nucleotide sequence of the coding region of homt2 wa s 89% homologous to this cDNA. Northern blot analysis showed that the transcript of homt1 was abundant in stems while the transcript of homt 2 accumulated in leaves. Immunohistochemical analysis with OMT-specifi c antiserum showed that the enzyme was localized in the xylem of stems and leaves but not in other tissues. Since the xylem is known as a li gnifying tissue, it seems likely that homt1 and homt2 are involved in the biosynthesis of lignin and that the expression of these genes is s ubject to tissue-specific control.