Developmental Regulation of Phenylpropanoid Biosynthesis in Leaves and Glandular Trichomes of Basil (Ocimum basilicum L.)

Basil (Ocimum basilicum L.) essential oil phenylpropenes have ecological and economic importance. These compounds are specifically synthesized and accumulate in basil peltate glandular trichomes, and their content and composition depend on plant developmental stage. Studies on gene expression and enzymatic activity indicate that the phenylpropene biosynthetic genes are developmentally regulated. These previous studies, however, did not systematically investigate the levels of gene expression, enzyme activity, and phenylpropene accumulation through plant development. In this study, we systematically investigated methylchavicol accumulation in basil leaves and the enzyme activities and gene expression of both chavicol O-methyltransferase (CVOMT) and eugenol O-methyltransferase (EOMT) in all leaves at four plant developmental stages. Methylchavicol accumulation decreased over time as the leaves matured. There was a significant correlation between methylchavicol accumulation and CVOMTand EOMTenzyme activities, suggesting that the levels of biosynthetic enzymes control the essential oil content. CVOMTand EOMT transcript expression levels, which decreased with leaf age, followed the same pattern in both whole leaves and isolated glandular trichomes, providing evidence for the first time that CVOMT transcript levels are developmentally regulated in basil glandular trichomes themselves and that differences in CVOMT expression observed in whole leaves are not solely the result of differences in glandular trichome density.