Stress Responses in Alfalfa (Medicago sativa L.)

Abstract

S-Adenosyl-L-methionine:caffeic acid 3-0-methyltransferase (COMT, EC 2.1.1.6) catalyzes the conversion of caffeic acid to ferulic acid, a key step in the biosynthesis of lignin monomers. We have isolated a functionally active cDNA clone (pCOMT1) encoding alfalfa (Medicago sativa L.) COMT by immunoscreening a XZAPII cDNA expression library with anti-(aspen COMT) antibodies. The derived amino acid sequence of pCOMT1 is 86% identical to that of COMT from aspen. Southern blot analysis indicates that COMT in alfalfa is encoded by at least two genes. Addition of an elicitor preparation from bakers' yeast to alfalfa cell suspension cultures resulted in a rapid accumulation of COMT transcripts, which reached a maximum level around 19 hours postelicitation. Northern blot analysis of total RNA from different organs of alfalfa plants at various developmental stages showed that COMT transcripts are most abundant in roots and stems. Transcripts encoding ATP: i-methionine-S-adenosyl transferase (AdoMet synthetase, EC 2.5.1.6), the enzyme responsible for the synthesis of the methyl donor for the COMT reaction, were coinduced with COMT transcripts in elicitor-treated cells and exhibited a similar pattern of expression to that of COMT in different organs of alfalfa plants at various stages of development.

An alternative methylation pathway in lignin biosynthesis in Zinnia.

“…OMT from the ice plant (Vernon and Bohnert, 1992). All of these OMTs, but not CCoAOMT, show significant amino acid similarity, especially in severa1 conserved regions identified for OMTs (Bugos et al, 1991). Some of these conserved regions are suggested to be involved in the SAM binding.…”

“…However, Zinnia CCoAOMT does not exhibit any significant similarity with COMT and some other OMTs from plants. COMT cDNAs or genes have been characterized from alfalfa (Gowri et al, 1991), aspen (Bugos et al, 1991), and maize (Collazo et al, 1992). Several other OMT cDNAs have also been isolated, including a putative OMT possibly involved in suberin biosynthesis from maize (Held et al, 1993), an isoliquiritigenin OMT from alfalfa (Maxwell et al, 1993), an orthodiphenol OMT from tobacco (Pellegrini et al, 1993), and a myoinositol 1 2 identity was determined according to both nucleotide and deduced amino acid sequence comparison and the activity assay in Escherichia coli.…”

“…They either use both caffeic acid and 5-hydroxyferulic acid (in angiosperm dicots) or mainly use caffeic acid (in gymnosperms) as substrates. Thus, only free hydroxycinnamic acids are considered to be the in vivo substrates of the OMTs, and caffeic acid O-methyltransferase (COMT) is the only one known to be involved in the methylation reaction of lignin biosynthesis (Grisebach et al, 1981;Bugos et al, 1991;Gowri et al, 1991;Collazo et al, 1992;Davin and Lewis, 1992).…”

The Root Hair “Infectome” of Medicago truncatula Uncovers Changes in Cell Cycle Genes and Reveals a Requirement for Auxin Signaling in Rhizobial Infection

“…There was also increased expression of genes encoding a cinnamic acid 4-hydroxylase, two 4-coumarate ligases, a chalcone synthase, and two chalcone reductases (CHRs), the latter being legume specific and acting downstream of chalcone synthase to produce the chalcone isoliquiritigenin (Figure 4; Supplemental Data Set 5, Phenylpropanoids). Notably, two genes involved in lignin biosynthesis from p-coumarate, caffeoyl-CoA O-methyltransferase and caffeic acid-O-methyltransferase (Gowri et al, 1991;Do et al, 2007), were repressed (data not shown), suggesting carbon flow within the pathway is directed mainly toward flavonoid biosynthesis.…”

Downregulation of Caffeic Acid 3-O-Methyltransferase and Caffeoyl CoA 3-O-Methyltransferase in Transgenic Alfalfa: Impacts on Lignin Structure and Implications for the Biosynthesis of G and S Lignin

“…Protein concentrations were determined using Bradford dye binding reagent (Bio-Rad) with BSA as standard. Enzyme activities were assayed essentially as described before (Gowri et al, 1991;Ni et al, 1996) with the following modifications. The assay mixtures contained 5 L of [ 14 CH 3 ]-S-adenosyl-L-Met (0.6 mM, 13 Ci/ mol), 5 L of caffeic acid (1 mM) or caffeoyl CoA (1 mM), 30 L of assay buffer (100 mM Tris-HC1, pH 7.5, 10% glycerol, 2 mM DTT, 0.2 mM MgC1 2 ), and 5 L of protein extract.…”