Similar Regulation Patterns of Choline Monooxygenase, Phosphoethanolamine N-Methyltransferase and S-Adenosyl-l-Methionine Synthetase in Leaves of the Halophyte Atriplex nummularia L.

Abstract

Glycinebetaine (betaine) highly accumulates as a compatible solute in certain plants and has been considered to play a role in the protection from salt stress. The betaine biosynthesis pathway of betaine-accumulating plants involves choline monooxygenase (CMO) as the key enzyme and phosphoethanolamine N-methyltransferase (PEAMT), which require S-adenosyl-L-methionine (SAM) as a methyl donor. SAM is synthesized by SAM synthetase (SAMS), and is needed not only for betaine synthesis but also for the synthesis of other compounds, especially lignin. We cloned CMO, PEAMT and SAMS isogenes from a halophyte Atriplex nummularia L. (Chenopodiaceous). The transcript and protein levels of CMO were much higher in leaves and stems than in roots, suggesting that betaine is synthesized mainly in the shoot. The regulation patterns of transcripts for SAMS and PEAMT highly resembled that of CMO in the leaves during and after relief from salt stress, and on a diurnal rhythm. In the leaves, the betaine content was increased but the lignin content was not changed by salt stress. These results suggest that the transcript levels of SAMS are co-regulated with those of PEAMT and CMO to supply SAM for betaine synthesis in the leaves.

Transcriptional response of glycinebetaine-related genes to salt stress and light in leaf beet

“…Transcripts for (or specific activities of) these betainerelated enzymes, with the exception of MS, are reported to be upregulated by salt stress in chenopod leaves (McCue and Hanson 1992;Russell et al 1998;Rontein et al 2001;Weretilnyk et al 2001;Tabuchi et al 2005). We previously reported that the regulation pattern of CMO transcripts resembles that of PEAMT and SAMSs in A. nummularia leaves under salt stress, after relief from salt stress and on a diurnal rhythm (Tabuchi et al 2005).…”

“…We previously reported that the regulation pattern of CMO transcripts resembles that of PEAMT and SAMSs in A. nummularia leaves under salt stress, after relief from salt stress and on a diurnal rhythm (Tabuchi et al 2005). In order to further examine the co-regulation of betaine-related genes in chenopods, we compared the Plant Biotechnology 23, 317-320 (2006) Transcriptional response of glycinebetaine-related genes to salt stress and light in leaf beet patterns of transcript expression in a broader range of betaine-related genes in B. vulgaris, which is one of the most important agricultural chenopod species.…”

“…Giovanelli et al (1985) showed that the synthesis of SAM is a major pathway involved in methionine metabolism in Lemna paucicostata, and we had previously suggested that the synthesized SAM is consumed mainly during betaine synthesis as a methyl group donor in the leaves of the chenopod Atriplex nummularia (Tabuchi et al 2005). Therefore, it may be assumed that the methionine synthesized in B. vulgaris leaves may be used primarily as a methyl donor for betaine synthesis.…”

“…lTriplEx2 cDNA library was constructed from the poly(A) RNA of the leaves using a SMART cDNA Library Construction Kit (Clontech, Palo Alto, CA, U.S.A.) as described earlier (Tabuchi et al 2005). The primary library contained 5ϫ10 5 plaqueforming units.…”

“…Additionally, we screened the cDNA library of leaf beet using the PEAMT gene of spinach (Nuccio et al 2000), metE gene of Catharanthus roseus (Eichel et al 1995), SAHH1 gene of Arabidopsis (Rocha et al 2005), and AtSDC gene of Arabidopsis (Rontein et al 2001) as probes; obtained the corresponding cDNA clones; and named them BvPEAMT1, BvMS1, BvSAHH1, and BvSDC1, respectively. The cDNA library was also screened using the AnSAMS1 gene of A. nummularia (Tabuchi et al 2005), and two types of cDNA clones were obtained. These genes were named BvSAMS1 and BvSAMS2.…”