Marchantia polymorpha, L, L

Yoshikawa, Mayu, Luo, Weifeng, Tanaka, Genta, Konishi, Yuka, Matsuura, Hideyuki & Takahashi, Kosaku, 2018, Wounding stress induces phenylalanine ammonia lyases, leading to the accumulation of phenylpropanoids in the model liverwort Marchantia polymorpha, Phytochemistry 155, pp. 30-36 : 32

2.3. Phenylalanine ammonia lyases in M. polymorpha

Flavonoids and bisbibenzyls are categorized as phenylpropanoids, and the initial step in the biosynthesis of compounds 1–3 is a PAL reaction, the non-oxidative deamination of phenylalanine to trans -cinnamic acid ( Thomas, 2010). PALs have been extensively studied with respect to the production of natural products such as flavonoids, lignin, and a variety of other phenolic compounds in plants. However, no detailed studies of PAL activity in M. polymorpha have been conducted.

Genomic analysis predicted the presence of ten Mp PAL genes in M. polymorpha ( Bowman et al., 2017) , which were designated Mp PAL1 (Mapoly0014s0211.1), Mp PAL2 (Mapoly0044s0114.1), Mp PAL3 (Mapoly0009s0173.1), Mp PAL4 (Mapoly0070s0061.1), Mp PAL5 (Mapoly0070s0065.1), Mp PAL6 (Mapoly0070s0068.1), Mp PAL7 (Mapoly0070s0071.1), Mp PAL8 (Mapoly0132s0049.1), Mp PAL9 (Mapoly0005s0086.1), and Mp PAL10 (Mapoly0005s0089.1). Similar to M. polymorpha , other land plants also have multiple PAL genes ( Bowman et al., 2017). The genes encoding cinnamate 4-hydroxylase (C4H) and 4-coumaroyl CoA ligase (4CL), which participate in phenylpropanoid biosynthesis, are also present in the genome of M. polymorpha . In contrast, no PAL, C4H, or 4CL genes are present in algae such as Chlamydomonas , though they do have genes that encode enzymes in the shikimate pathway, which provides aromatic amino acids such as phenylalanine and tyrosine ( Bowman et al., 2017). Based on genomic data from several plants, phenylpropanoids are considered to be characteristic specialized metabolites in land plants.

Phylogenetic analysis revealed that MpPAL2-10 formed a cluster that was separate from that of MpPAL1 and the other PALs of the model moss Physcomitrella patens and flowering plants ( Fig. S2 ). These results suggested that MpPAL1 is an ancestral land plant PAL. Amino acid sequence alignment analysis of the MpPALs revealed that eight of them have the conserved active site amino acid sequence Ala-Ser-Gly ( Fig. S3 ). Cyclization of Ala-Ser-Gly produces the cofactor of the PAL reaction, 3,5-dihydro-5-methylidene-4 H -imidazole-4-one (MIO) ( Schuster and J Rétey, 1995; Alunni et al., 2003; Calabrese et al., 2004). However, the predicted amino acid sequence of MpPAL10 is much shorter than that of the other predicted MpPALs and does not contain the conserved active site amino acid sequence Ala-Ser-Gly. Consequently, MpPAL10 likely does not have PAL activity. In the conserved amino acid sequence that forms MIO in MpPAL2, the Ser residue is substituted by Ala, a change that significantly reduced PAL activity in Petroselinum crispum L. ( Schuster and Rétey, 1995); therefore, MpPAL2 likely has weak PAL activity.

Figures

Fig. 2. The structures of luteolin (1), apigenin (2), and isoriccardin C (3).

Fig. 3. Accumulation of luteolin (1), apigenin (2), and isoriccardin C (3) induced by wounding in M. polymorpha. M. polymorpha plants were grown on 1/2 Gamborg's B5 medium containing 1.4% agar for 30 days and then subjected to wounding treatment. Plants were harvested at the indicated time. Data represent means ± S.D. of three separate experiments. The asterisks represent significant differences between wounded and control plants (Student's t-test, *p <0.05, **p <0.01).