Stress Responses in Alfalfa (XXI. Activation of Caffeic Acid 3-O-Methyltransferase and Caffeoyl Coenzyme A 3-O-Methyltransferase Genes Does Not Contribute to Changes in Metabolite Accumulation in Elicitor-Treated Cell-Suspension Cultures)

Abstract

Transcription of genes encoding i-phenylalanine ammonia-lyase (PAL), the first enzyme of the phenylpropanoid pathway, and caffeic acid 3-Omethyltransferase (COMT) and caffeoyl COA 3 -0 methyltransferase (CCOMT), enzymes involved in the synthesis of lignin and wall-esterified phenolic compounds, was strongly activated in elicitor-treated cell-suspension cultures of alfalfa (Medicago safiva 1.). However, consequent changes in the extractable activities of COM1 and CCOMT were small to nonexistent compared with a 15-to 16-fold increase in PAL activity. Only low levels of COMT and CCOMT transcripts were reflected in the total and polysomal RNA fractions compared with PAL transcripts. Elicited cell cultures did not accumulate lignin or the products of COM1 and CCOMT in the soluble and wall-esterified phenolic fractions. In one alfalfa cell line in which elicitation resulted in very high PAL activity and increased deposition of methoxyl groups in the insoluble wall fraction, there was still no change in COM1 and CCOMT activities. Overall, these results indicate that the initial gene transcription events in elicited cells may be less selective than the subsequent metabolic changes, highlighting the importance of posttranscriptional events in the control of phenylpropanoid biosynthesis.

Water Deficits Affect Caffeate O-Methyltransferase, Lignification, and Related Enzymes in Maize Leaves. A Proteomic Investigation

“…The coordinated expression of several of these genes has already been reported. Transcription of PAL, SAMS, and COMT genes was induced in elicited cells of alfalfa (Gowri et al, 1991;Ni et al, 1996). Increased accumulation of SAMS transcripts or protein has been repeatedly observed in tissues where lignification occurs, i.e.…”

Characterization and Expression of Caffeoyl-Coenzyme A 3-O-Methyltransferase Proposed for the Induced Resistance Response of Vitis vinifera L

“…V . vinifera thus differs from alfalfa, in which de novo transcription of CCoAOMT seems to occur without consequent translation (Ni et al, 1996). The accumulation of lignin-like materials for cell wall reinforcement was correlated with resistance in severa1 host-pathogen interactions (Hammerschmidt et al, 1985;Tiburzy and Reisener, 1990;Reimers and Leach, 1991), which appears to apply also to grapevine (Weber, 1992), and the physiological significance of CCoAOMT for cell wall reinforcement has been outlined in other plant systems (Schmitt et al, 1991;Matern et al, 1995).…”

Cell-Specific and Conditional Expression of Caffeoyl-Coenzyme A-3-O-Methyltransferase in Poplar

“…Most of the genes that code for enzymes of the lignin biosynthesis pathway, such as PAL, 4CL, COMT, and cinnamate 4-hydroxylase (C4H), have been reported to be induced by wounding, elicitors, and/or fungal infection (Baucher et al, 1998). CCoAOMT activity has been extensively studied in response to elicitors in cell suspension culture (Kneusel et al, 1989;Kü hnl et al, 1989;Schmitt et al, 1991;Ni et al, 1996;Busam et al, 1997). Transient expression assays performed with PCCoAOMT-GUS constructs in parsley protoplasts showed a high expression level in response to elicitation (Grimmig and Matern, 1997).…”