Supplementary UV-B Radiation Effects on Photosynthetic Characteristics and Important Secondary Metabolites in Eucommia ulmoides Leaves

Identification of GiOMT gene family in Glycyrrhiza inflata bat and expression analysis under UV-B stresses

BACKGROUND

O-Methyltransferase (OMTs) is a class of conserved multifunctional enzymes that play important roles in plant developmental regulation, hormone signaling, secondary metabolite synthesis and abiotic stress response. The GiOMT gene family has been identified and analyzed in species such as citrus, alfalfa, Populus and grape, but has not been reported in Glycyrrhiza inflata Bat.

RESULTS

In this study, we systematically identified and analyzed the GiOMT gene family of G. inflata by bioinformatics, and analyzed their physicochemical properties, conserved motifs, conserved structural domains, gene structures, phylogenetic relationships, chromosomal localization and fragment duplications, and the expression patterns of GiOMT genes in combination with transcriptomic data and qRT-PCR. The results showed that a total of 41 GiOMTs were identified in G. inflata, which were named GiOMT1 ~ GiOMT41 based on their chromosomal locations. Protein characterization showed that 29 GiOMT proteins were hydrophilic and 12 GiOMT proteins were hydrophobic. Subcellular predicted localization revealed that most GiOMT proteins localized in the cytoplasm and chloroplasts. Phylogenetic relationships showed that the OMT genes of three species, G. inflata, Arabidopsis and alfalfa, were distributed in three taxa, while the GiOMT genes were distributed in taxa I and II. Promoters of GiOMT genes contained light responsive element and many hormone responsive elements. The expression levels of GiOMT genes under UV-B stress were varied, indicating that GiOMT gene was in response to abiotic stresses in G. inflata.

CONCLUSION

In this study, we investigated the genome-wide identification, structure, evolution and expression analysis of the GiOMT gene in G. inflata. The basal sequence of GiOMT genes was highly conserved throughout the evolutionary history of G. inflata. Most of the GiOMT genes were highly expressed in roots and were involved in the response to UV-B stress. The GiOMT genes may lead to the accumulation of flavonoids and enhancement of G. inflata quality and drug activity in G. inflata under UV-B radiation.

Ultraviolet-B Radiation Stimulates Flavonoid Biosynthesis and Antioxidant Systems in Buckwheat Sprouts

Abiotic stress not only elevates the synthesis of secondary metabolites in plant sprouts but also boosts their antioxidant capacity. In this study, the mechanisms of flavonoid biosynthesis and antioxidant systems in buckwheat sprouts exposed to ultraviolet-B (UV-B) radiation were investigated. The findings revealed that UV-B treatment significantly increased flavonoid content in buckwheat sprouts, with 3-day-old sprouts exhibiting a flavonoid content 1.73 times greater than that of the control treatment. UV-B radiation significantly increased the activities of key enzymes involved in flavonoid biosynthesis (phenylalanine ammonia-lyase, 4-coumarate-CoA ligase, cinnamate 4-hydroxylase, and chalcone synthase) and the relative expression levels of the corresponding genes. Although UV-B radiation caused damage to the cell membranes of buckwheat sprouts, promoting increases in hydrogen peroxide and malondialdehyde content and inhibiting the growth of sprouts, importantly, UV-B radiation also significantly increased the activities of catalase, peroxidase, and superoxide dismutase as well as the relative expression levels of the corresponding genes, thus enhancing the antioxidant system of buckwheat sprouts. This enhancement was corroborated by a notable increase in ABTS, DPPH, and FRAP radical scavenging activities in 3-day-old sprouts subjected to UV-B radiation. Additionally, UV-B radiation significantly increased chlorophyll a and chlorophyll b contents in sprouts. These results suggest that UV-B radiation is advantageous for cultivating buckwheat sprouts with increased flavonoid content and enhanced antioxidant capacity.

Four New Furofuran Lignans from Phryma leptostachya Inhibit the Accumulation of Molting Hormones in Armyworm

Furofuran lignans have been identified as the main substances responsible for the biological activities of the plant genus Phryma. Here, four new phrymarolin-type leptolignans A-D (7-10) and eight previously known lignans were isolated from P. leptostachya. Of these, nine exhibited significant antifeedant activity against armyworm (Mythimna separata) through a dual-choice bioassay, with the EC50 values ranging from 0.58 to 10.08 μg/cm2. In particular, the newly identified lignan leptolignan A (7) showed strong antifeedant activity, with an EC50 value of 0.58 ± 0.34 μg/cm2. Further investigation found that leptolignan A can inhibit the growth and nutritional indicators in the armyworm M. separata. The concentrations of two molting hormones, 20-hydroxyecdysone and ecdysone, were also found to decrease significantly following the treatment of the armyworms with the lignan, implying that the target of the P. leptostachya lignan may be involved in 20-hydroxyecdysone and ecdysone synthesis. These results enrich our knowledge of P. leptostachya metabolite structural diversity, and provide a theoretical basis for the control of armyworm using lignans.

Cloning and functional characterization of a cinnamate 4-hydroxylase gene from the hornwort Anthoceros angustus

Hornworts, as the sister group to liverworts and mosses, comprise bryophytes, which are critical in understanding the evolution of key land plant traits. Cinnamate 4-hydroxylase (C4H) catalyzes the second step of the phenylpropanoid pathway to synthesize the precursor of numerous phenolic compounds, such as lignin and flavonoids. However, C4H in the hornwort Anthoceros angustus has not yet been cloned and functionally characterized. In this work, we screened the transcriptome database of A. angustus and identified one C4H gene, AnanC4H. AnanC4H maintained conserved cytochrome P450 domains with other typical plant C4Hs. Ultraviolet B irradiation and exogenous application of methyl jasmonate (MeJA) induced the expression of AnanC4H to varying degrees. The coding sequence of AnanC4H was expressed in yeast, and the recombinant proteins were isolated. The recombinant proteins of AnanC4H catalyzed the conversion of trans-cinnamic acid to p-coumaric acid and catalyzed the conversion of 3-hydroxycinnamic acid to caffeic acid. AnanC4H showed higher affinity for trans-cinnamic acid than for 3-hydroxycinnamic acid, but there was no significant difference in the catalytic efficiency of AnanC4H for the two substrates in vitro. Moreover, the expression of AnanC4H in Arabidopsis thaliana led to an increase in both the lignin content and the number of lignified cells in stems. However, there was no significant change in flavonoid content in transgenic Arabidopsis plants.

Identification of One O-Methyltransferase Gene Involved in Methylated Flavonoid Biosynthesis Related to the UV-B Irradiation Response in Euphorbia lathyris

Flavonoids are ubiquitous polyphenolic compounds that play a vital role in plants' defense response and medicinal efficacy. UV-B radiation is a vital environmental regulator governing flavonoid biosynthesis in plants. Many plants rapidly biosynthesize flavonoids as a response to UV-B stress conditions. Here, we investigated the effects of flavonoid biosynthesis via UV-B irradiation in Euphorbia lathyris. We found that exposure of the E. lathyris callus to UV-B radiation sharply increased the level of one O-methyltransferase (ElOMT1) transcript and led to the biosynthesis of several methylated flavonoids. The methyltransferase ElOMT1 was expressed heterologously in E. coli, and we tested the catalytic activity of recombinant ElOMT1 with possible substrates, including caffeic acid, baicalin, and luteolin, in vitro. ElOMT1 could efficiently methylate when the hydroxyl groups were contained in the core nucleus of the flavonoid. This molecular characterization identifies a methyltransferase responsible for the chemical modification of the core flavonoid structure through methylation and helps reveal the mechanism of methylated flavonoid biosynthesis in Euphorbiaceae. This study identifies the O-methyltransferase that responds to UV-B irradiation and helps shed light on the mechanism of flavonoid biosynthesis in Euphorbia lathyris.