Red Light Regulates the Metabolite Biosynthesis in the Leaves of “Huangjinya” Through Amino Acid and Phenylpropanoid Metabolisms

“Huangjinya” is a light-sensitive albino variety and is widely cultivated in China. It has been proved that red light could promote the vegetable growth of plants. However, the mechanism of “Huangjinya” in response to a red light is unclear. This study used high-throughput sequencing technology to analyze the transcriptome of tender shoots of “Huangjinya” under the white and red light supplement conditions. At the same time, liquid chromatography tandem mass spectrometry (LC-MS) was used to analyze metabolite changes under different light conditions. Transcriptome analysis revealed that a total of 174 differentially expressed genes (DEGs) were identified after the red light supplement. Kyoto encyclopedia of genes and genomes (KEGG) classification indicated that amino acid metabolism enriched the most DEGs. In addition, two phenylpropanoid metabolism-related genes and five glutathione S-transferase genes (CsGSTs) were found to be expressed differently. Metabolome analysis revealed that 193 differential metabolites were obtained. Being the same as transcriptome analysis, most differential metabolites were enriched in amino acids, sweet and umami tasting amino acids were increased, and bitter-tasting amino acids were decreased after the red light supplement. In summary, red light supplementary treatment may be propitious to the quality of “Huangjinya” due to its regulatory effect on amino acid metabolism. Also, CsGSTs involved phenylpropanoid metabolism contributed to tea quality changes in “Huangjinya.”

Phenylpropanoid metabolism enzyme activities and gene expression in postharvest melons inoculated with Alternaria alternata

This study explored the mechanism of melon resistance to Alternaria alternata (A. alternata) infection in Jiashi and 86-1 melons. Melons were inoculated with A.alternata and the change in lesion diameter was measured. The changes in cinnamic acid-4-hydroxylase (C4H), phenylalanine ammonia lyase (PAL), and 4-coumaric acid coenzyme A ligase (4CL) activity and gene expression were studied in the pericarp tissues of Jiashi and 86-1 melons. The lesion diameter was smaller in Jiashi melon than in 86-1 melon, and the pericarp lesions were smaller than pulp lesions, indicating that Jiashi melon can resist A. alternata infection better than 86-1 melon. After inoculation with A. alternata, the C4H, PAL, and 4CL activities of Jiashi and 86-1 melons peaked in the middle and late storage period, and the peak was higher in Jiashi melons. The gene expression changes were consistent with the enzyme activity. The C4H, PAL, and 4CL gene expression was significantly higher in Jiashi melon pericarp than in 86-1 melon, and the C4H, PAL, and 4CL activities in Jiashi melon were positively correlated with their gene expression, confirming the role of phenylpropanoid metabolism enzymes in resistance to A. alternata.

Transcriptome Profiling Reveals the Effects of Nitric Oxide on the Growth and Physiological Characteristics of Watermelon under Aluminum Stress

Excessive aluminum ions (Al3+) in acidic soil can have a toxic effect on watermelons, restricting plant growth and reducing yield and quality. In this study, we found that exogenous application of nitric oxide (NO) could increase the photochemical efficiency of watermelon leaves under aluminum stress by promoting closure of leaf stomata, reducing malondialdehyde and superoxide anion in leaves, and increasing POD and CAT activity. These findings showed that the exogenous application of NO improved the ability of watermelon to withstand aluminum stress. To further reveal the mitigation mechanism of NO on watermelons under aluminum stress, the differences following different types of treatments—normal growth, Al, and Al + NO—were shown using de novo sequencing of transcriptomes. In total, 511 differentially expressed genes (DEGs) were identified between the Al + NO and Al treatment groups. Significantly enriched biological processes included nitrogen metabolism, phenylpropane metabolism, and photosynthesis. We selected 23 genes related to antioxidant enzymes and phenylpropane metabolism for qRT-PCR validation. The results showed that after exogenous application of NO, the expression of genes encoding POD and CAT increased, consistent with the results of the physiological indicators. The expression patterns of genes involved in phenylpropanoid metabolism were consistent with the transcriptome expression abundance. These results indicate that aluminum stress was involved in the inhibition of the photosynthetic pathway, and NO could activate the antioxidant enzyme defense system and phenylpropane metabolism to protect cells and scavenge reactive oxygen species. This study improves our current understanding by comprehensively analyzing the molecular mechanisms underlying NO-induced aluminum stress alleviation in watermelons.

A rice QTL GS3.1 regulates grain size through metabolic-flux distribution between flavonoid and lignin metabolons without affecting stress tolerance

Grain size is a key component trait of grain weight and yield. Numbers of quantitative trait loci (QTLs) have been identified in various bioprocesses, but there is still little known about how metabolism-related QTLs influence grain size and yield. The current study report GS3.1, a QTL that regulates rice grain size via metabolic flux allocation between two branches of phenylpropanoid metabolism. GS3.1 encodes a MATE (multidrug and toxic compounds extrusion) transporter that regulates grain size by directing the transport of p-coumaric acid from the p-coumaric acid biosynthetic metabolon to the flavonoid biosynthetic metabolon. A natural allele of GS3.1 was identified from an African rice with enlarged grains, reduced flavonoid content and increased lignin content in the panicles. Notably, the natural allele of GS3.1 caused no alterations in other tissues and did not affect stress tolerance, revealing an ideal candidate for breeding efforts. This study uncovers insights into the regulation of grain size though metabolic-flux distribution. In this way, it supports a strategy of enhancing crop yield without introducing deleterious side effects on stress tolerance mechanisms.

Molecular and Biochemical Characterization of Two 4-Coumarate: Coa Ligase Genes in Tea Plant (Camellia Sinensis)

Tea is rich in flavonoids benefiting human health. Lignin is essential for tea plant growth. Both flavonoids and lignin defend plants from stresses. The biosynthesis of lignin and flavonoids shares a key intermediate, p-coumaroyl-CoA, which is formed from p-coumaric acid catalyzed by p-coumaric acid: CoA ligase (4CL). Herein, we reported two 4CL paralogs from tea plant, Cs4CL1 and Cs4CL2, which were a member of class I and II, respectively. Cs4CL1 was mainly expressed in roots and stems, while Cs4CL2 was mainly expressed in leaves. The promoter of Cs4CL1 had AC, light and stress-inducible (LSI), and meristem-specific elements, while that of Cs4CL2 had AC and LSI elements only. Moreover, the promoter of Cs4CL1 had two more stress-inducible elements than Cs4CL2 had and the two promoters had six different light-inducible elements. These features suggested their differences in their responses to environmental conditions. Three stress treatments indicated that the expression of Cs4CL1 was sensitive to mechanical wounding, while the expression of Cs4CL2 was UV-B-inducible. Enzymatic assay showed that both recombinant Cs4CL1 and Cs4CL2 transformed p-coumaric acid, ferulic acid and caffeic acid to their corresponding CoA ethers. Kinetic analysis indicated that the recombinant Cs4CL1 preferred to catalyze caffeic acid, while the recombinant Cs4CL2 favored to catalyze p-coumaric acid. The overexpression of both Cs4CL1 and Cs4CL2 increased the levels of chlorogenic acid and total lignin in transgenic tobacco seedlings. In addition, the overexpression of Cs4CL2 increased the levels of three flavonoid compounds. These findings indicate the differences of Cs4CL1 and Cs4CL2 in the phenylpropanoid metabolism.

Re-engineering Plant Phenylpropanoid Metabolism With the Aid of Synthetic Biosensors

Phenylpropanoids comprise a large class of specialized plant metabolites with many important applications, including pharmaceuticals, food nutrients, colorants, fragrances, and biofuels. Therefore, much effort has been devoted to manipulating their biosynthesis to produce high yields in a more controlled manner in microbial and plant systems. However, current strategies are prone to significant adverse effects due to pathway complexity, metabolic burden, and metabolite bioactivity, which still hinder the development of tailor-made phenylpropanoid biofactories. This gap could be addressed by the use of biosensors, which are molecular devices capable of sensing specific metabolites and triggering a desired response, as a way to sense the pathway’s metabolic status and dynamically regulate its flux based on specific signals. Here, we provide a brief overview of current research on synthetic biology and metabolic engineering approaches to control phenylpropanoid synthesis and phenylpropanoid-related biosensors, advocating for the use of biosensors and genetic circuits as a step forward in plant synthetic biology to develop autonomously-controlled phenylpropanoid-producing plant biofactories.

Morphological characteristics and transcriptome analysis at different anther development stages of the male sterile mutant MS7–2 in Wucai (Brassica campestris L.)

Background The discovery of male sterile materials is of great significance for the development of plant fertility research. Wucai (Brassica campestris L. ssp. chinensis var. rosularis Tsen) is a variety of non-heading Chinese cabbage. There are few studies on the male sterility of wucai, and the mechanism of male sterility is not clear. In this study, the male sterile mutant MS7–2 and the wild-type fertile plant MF7–2 were studied. Results Phenotypic characteristics and cytological analysis showed that MS7–2 abortion occurred at the tetrad period. The content of related sugars in the flower buds of MS7–2 was significantly lower than that of MF7–2, and a large amount of reactive oxygen species (ROS) was accumulated. Through transcriptome sequencing of MS7–2 and MF7–2 flower buds at three different developmental stages (a–c), 2865, 3847, and 4981 differentially expressed genes were identified in MS7–2 at the flower bud development stage, stage c, and stage e, respectively, compared with MF7–2. Many of these genes were enriched in carbohydrate metabolism, phenylpropanoid metabolism, and oxidative phosphorylation, and most of them were down-regulated in MS7–2. The down-regulation of genes involved in carbohydrate and secondary metabolite synthesis as well as the accumulation of ROS in MS7–2 led to pollen abortion in MS7–2. Conclusions This study helps elucidate the mechanism of anther abortion in wucai, providing a basis for further research on the molecular regulatory mechanisms of male sterility and the screening and cloning of key genes in wucai.

Sodium Hydrosulfide Induces Resistance Against Penicillium expansum in Apples by Regulating Hydrogen Peroxide and Nitric Oxide Activation of Phenylpropanoid Metabolism

As a multifunctional signaling molecule, hydrogen sulfide (H2S) has been reported to induce plant responses to a variety of abiotic stresses. However, there are no reports on H2S treatment inducing resistance in apples against Penicillium expansum, a biotic factor, and its possible mechanism of action. In this study, fumigating apples with 5 mM sodium hydrosulfide (NaHS), the exogenous donor of H2S, for 12 h reduced the diameter of lesions in fruit colonized by P. expansum. NaHS treatment markedly promoted the synthesis of endogenous H2S, hydrogen peroxide (H2O2), and nitrogen oxide (NO). In vivo NaHS treatment enhanced the activities of phenylalanine ammonia-lyase, cinnamate 4-hydroxylase, p-coumarate:coenzyme A ligase isoenzymes, caffeoyl-CoA-O-methyltransferase, caffeic acid-O-methyltransferase, ferulic acid-5-hydroxylase, cinnamyl-CoA reductase, and cinnamyl-alcohol dehydrogenase. The treatment also facilitated the production of specific phenolic acids, such as cinnamic acid, p-coumaric acid, caffeic acid, ferulic acid, and sinapic acid; total phenolic compounds; p-coumaryl alcohol; coniferyl alcohol; sinapyl alcohol; and lignin. NaHS treatment induced resistance against P. expansum in apples through H2O2- and NO-mediated activation of phenylpropanoid metabolism.