Expression profile of a PAL gene from Astragalus membranaceus var. Mongholicus and its crucial role in flux into flavonoid biosynthesis

Abstract

An important traditional Chinese medicine herb, Astragalus membranaceus var. Mongholicus, whose dried root is known as Radix astragali ("Huangqi" in Chinese), has high flavonoid content as an essential active constituent. Phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) catalyzes the first and also a rate-limiting step in phenylpropanoid pathway, which supplies precursors for a variety of secondary metabolites including flavonoids. A PAL gene, designated AmPAL1 (GenBank accession no. AY986506), was isolated from A. membranaceus var. Mongholicus with a full-length cDNA of 2562 nucleotides and an open reading frame of 2154 bp. Northern blot analysis revealed that AmPAL1 expressed universally in different organs, and its expression was markedly induced by UV irradiation, mechanical wounding, and white light irradiation on etiolated seedlings, with some distinctive responsive properties. Content of a typical flavonoid, quercetin, in A. membranaceus var. Mongholicus of different ages correlated with PAL enzymatic activity. Transgenic tobacco plants harboring AmPAL1 under the control of the CaMV35S promoter showed significantly increased PAL activity and correlatively increased quercetin content than those in non-transformed plants. These results indicate that PAL is maybe a key point for flux into flavonoid biosynthesis in the genetic control of secondary metabolism in A. membranaceus var. Mongholicus.

Study of the Relationship between Genetics and Geography in Determining the Quality of Astragali Radix

“…The concentration of each compound was as follows: 0.602 mg/ml (1), 0.604 mg/ml (2), 0.600 mg/ml (3), 0.306 mg/ml (4), 1.086 mg/ml (5), 0.580 mg/ml (6), 0.206 mg/ml (7) and 0.202 mg/ml (8). The stock solution was further diluted with methanol to make serial concentrations for the calibration curves.…”

Modulation of enzyme activities and expression of genes related to primary and secondary metabolism in response to UV-B stress in cucumber (Cucumis sativusL.)

“…These results are in accordance with the increased level of PAL activity and with the accumulation of phenolic compounds measured in our experiments. Other studies showed that UV-absorbing compounds, mainly flavonoid and sinapate esters, other metabolites of the phenylpropanoid pathway, markedly accumulated upon UV-B irradiation, which is a consequence of an increase in transcription of PAL and other genes of phenylpropanoid enzymes (Shirley 1996, Liu et al 2006). …”

RNAi-mediated suppression of the phenylalanine ammonia-lyase gene in Salvia miltiorrhiza causes abnormal phenotypes and a reduction in rosmarinic acid biosynthesis

“…It also acts in the synthesis of main active ingredients within many plants, e.g., caffeoyl quinic acids in Coffea canephora (Mahesh et al 2006) and quercetin in Astragalus membranaceus var. mongholicus (Liu et al 2006b). Razzaque and Ellis (1977) have shown that PAL is important for rosmarinic acid biosynthesis in Coleus blumei, and Chen and Chen (2000) have suggested that this enzyme has the same role in S. miltiorrhiza.…”