REGULATION OF THE CINNAMATE 4-HYDROXYLASE (CYP73A1) IN JERUSALEM-ARTICHOKE TUBERS IN RESPONSE TO WOUNDING AND CHEMICAL TREATMENTS

trans-Cinnamate 4-hydroxylase (C4H) is a plant-specific cytochrome (P4 50) that is encoded by the gene CYP73A and catalyzes the second step o f the multibranched phenylpropanoid pathway. Increases in C4H activity in response to physical and chemical stresses have been well document ed, but the mechanism of these increases has never been studied in det ail. This paper reports on the regulatory mechanism controlling C4H ac tivity in Jerusalem artichoke (Helianthus tuberosus) tubers in respons e to wounding and chemical treatments. We compared induction of C4H an d other P450-catalyzed activities. C4H was moderately induced by chemi cals relative to other P450s. Increases in enzyme activity, C4H protei n, and transcripts were quantified and compared in tuber tissue 48 h a fter wounding and chemical treatments. Our data suggest that induction of the enzyme activity results primarily from gene activation. Time-c ourse experiments were performed after wounding and aminopyrine treatm ent. Compared with wounded tissues, aminopyrine triggered an additiona l and delayed peak of transcript accumulation. The timing of the induc ed changes in activity, protein, and transcripts confirms that C4H ind uction results primarily from an increase in CYP73A1 mRNA, in both wou nded and aminopyrine-treated tissues. However, posttranscriptional mec hanisms might also contribute to the regulation of C4H activity.