Phenylalanine ammonia lyase functions as a switch directly controlling the accumulation of calycosin and calycosin-7-O- -D-glucoside in Astragalus membranaceus var. mongholicus plants

Abstract

Previously it had been shown that calycosin and calycosin-7-O-beta-D-glucoside (CGs) accumulate in whole plants, mainly in leaves, of Astragalus membranaceus Bge. var. mongholicus (Bge.) Hsiao (A. mongholicus) plants in response to low temperature. In this work, it was demonstrated that the influences of different conditions on CGs biosynthesis, by examining the changes in CGs content, as well as the expression of related genes, including phenylalanine ammonia lyase (PAL1), cinnamic acid 4-hydroxylase (C4H), chalcone synthase (CHS), chalcone reductase (CHR), chalcone isomerase (CHI), isoflavone synthase (IFS), and isoflavone 3'-hydroxylase (I3'H). The seven gene mRNAs accumulated in leaves of A. mongholicus upon exposure to low temperature in a light-dependent manner, though they exhibited different expression patterns. Transcriptions of CHS, CHR, CHI, IFS, and I3'H of the calycosin-7-O-beta-D-glucoside pathway were all up-regulated when plants were transferred from 16 degrees C to 2 degrees C or 25 degrees C or from 2 degrees C (kept for 24 h) to 25 degrees C. However, fluctuations in temperature influenced differently the transcriptions of PAL1 and C4H of the general phenylpropanoid pathway in leaves. Moreover, the amount of PAL1 expression changed sharply up and down, consistent with the variation of the content of CGs. PAL enzyme activity appears to be the limiting factor in determining the CGs levels. The inhibitor of PAL enzyme, L-alpha-aminooxy-beta-phenylpropionic acid, almost entirely shut down CGs accumulation at low temperature. All these results confirmed that PAL1, as a smart gene switch, directly controls the accumulation of CGs in A. mongholicus plants, in a light-dependent manner, during low temperature treatment.

Flavonoids and Antioxidative Enzymes in Temperature-Challenged Roots of Scutellaria baicalensis Georgi

“…PAL expression was increased in response to lower temperatures, which is in agreement with a corresponding increase in the fl avonoid content in the leaves of tomato (Pan et al, 2008). In the roots of S. baicalensis, the transcript levels of PAL did not change after high-and low-temperature treatment, indicating that the changes of active compounds were not due to the alterations in the rate of fl avonoid biosynthesis.…”

Disruption of Poly(ADP-ribosyl)ation Mechanisms Alters Responses of Arabidopsis to Biotic Stress

“…3C). Treatment of seedlings with L-a-aminooxy-b-phenylpropionic acid (AOPP), a chemical inhibitor of PAL activity (Kudakasseril and Minocha, 1986;Prats et al, 2007;Pan et al, 2008), reduces the accumulation of this pigment ( Fig. 3D), suggesting that this pigment is likely a product of the phenylpropanoid pathway.…”

Transcriptional Profiling and Molecular Characterization of Astragalosides, Calycosin, and Calycosin-7-O-β-d-glucoside Biosynthesis in the Hairy Roots of Astragalus membranaceus in Response to Methyl Jasmonate

“…AmPAL1, AmC4H1, AmCHS1, chalcone reductase (AmCHR), AmCHI, isoflavone synthase (AmIFS), and isoflavone 3′-hydroxylase (AmI3′H), which are involved in calycosin and CG biosynthetic pathways (Figure 7), 9 were also found in the A. membranaceus transcriptome library. In addition, seven new full-length coding sequences (AmPAL2, AmPAL3, AmC4H2, Am4CL, AmCHS2, AmIOMT, and UDP-glucose:calycosin 7-O-glucosyltransferase (AmUCGT)) were identified (Table 4).…”