In this research, qualitative characteristics were studied under different post-harvest treatments in Hass and Fuerte cultivars of avocado (Persea americana) fruits. The post-harvest treatments performed in fruits of these cultivars comprised Ethrel application and plastic film (membrane) covering. The measurements of qualitative characteristics were related to color; flesh consistency; measurements of titratable acidity, total soluble solids, percentage of total phenolic contents, and ascorbic peroxidase activity; and the real-time (quantitative) polymerase chain reaction (qPCR) of gene expression and enzyme activities of phenylalanine ammonia-lyase (PAL) and beta-galactosidase (β-gal). The experiments found that the application of plastic film has excellent results in retaining qualitative characteristics and enzyme activities via maintaining firmness in higher levels. The plastic film covering appeared to delay ripening without the use of chemicals and, therefore, it has the potential to extend the duration of the post-harvest life of the avocado fruit. Variations between the two cultivars were found in the measurements of total soluble solids (Fuerte cultivar showed an increase of 22%, whereas Hass cultivar showed an increase of 120% in Brix values) and total phenolic contents (Fuerte cultivar showed a decrease of 16% and Hass cultivar showed an increase of 29%). It is worth noting that PAL\'s activity increased significantly (over 44%), as compared to other treatments, and β-galactosidase\'s activity decreased, as compared to other treatments. In conclusion, plastic film covering results in a decrease in the activity of β-galactosidase, as shown by the reaction of hydrolysis (enzyme activity) but also from the expression of the related genes.

Black rots lead to great economic losses in winter jujube industry. The objective of this research was to delve into the underlying mechanisms of enhanced resistance of winter jujube fruit to black rot by L-Methionine (Met) treatment. The findings revealed that the application of Met significantly curtailed lesion diameter and decay incidence in winter jujube fruit. The peroxidase (POD) activity in the Met-treated jujubes was 3.06-fold that in the control jujubes after 4 d of treatment. By day 8, the activities of phenylalanine ammonia-lyase (PAL), chitinase (CHI) and β-1,3-glucanase (GLU) in the Met-treated jujubes had surged to their zenith, being 1.39, 1.22, and 1.52 times in the control group, respectively. At the end of storage, the flavonoid and total phenol content remained 1.58 and 1.06 times than that of the control group. Based on metabolomics and transcriptomics analysis, Met treatment upregulated 6 key differentially expressed metabolites (DEMs) (succinic acid, trans-ferulic acid, salicylic acid, delphinium pigments, (S)-abscisic acid, and hesperidin-7-neohesperidin), 12 key differentially expressed genes (DEGs) (PAL, CYP73A, COMT, 4CL, CAD, POD, UGT72E, ANS, CHS, IAA, TCH4 and PR1), which were involved in phenylpropanoid biosynthesis pathway, flavonoid biosynthesis pathway and plant hormone signal transduction pathway. Further analysis revealed that the most of the enzymes, DEMs and DEGs in this study were associated with both antioxidant and disease resistance. Consequently, Met treatment enhanced disease resistance of winter jujube fruit by elevating antioxidant capacity and triggering defense response. This study might provide theoretical support for utilizing Met in the management and prevention of post-harvest black rot in winter jujube.

Bamboo, renowned as the fastest-growing plant globally, matures within an astonishingly short period of 40-50 days from shoots, reaching heights of 10-20 meters. Moreover, it can be harvested for various uses within 3-5 years. Bamboo exhibits exceptional mechanical properties, characterized by high hardness and flexibility, largely attributed to its lignin content. Phenylalanine ammonia-lyase (PAL) catalyzes the crucial initial step in lignin biosynthesis, but its precise role in bamboo lignification processes remains elusive. Thus, elucidating the functions of PAL genes in bamboo lignification processes is imperative for understanding its rapid growth and mechanical strength. Here, we systematically identified and classified PAL genes in Moso bamboo, ensuring nomenclature consistency across prior studies. Subsequently, we evaluated PAL gene expression profiles using publicly available transcriptome data. The downregulation of PePALs expression in Moso bamboo through in planta gene editing resulted in a decrease in PAL activity and a subsequent reduction in lignin content. In contrast, overexpression of PePAL led to enhanced PAL activity and an increase in lignin content. These findings highlight the critical role of PAL in the lignin biosynthesis process of Moso bamboo, which will help to unravel the mechanism underpinning bamboo\'s rapid growth and mechanical strength, with a specific emphasis on elucidating the functions of PAL genes.

Phenylpropanoids, a class of specialized metabolites, play crucial roles in plant growth and stress adaptation and include diverse phenolic compounds such as flavonoids. Phenylalanine ammonia-lyase (PAL) and chalcone synthase (CHS) are essential enzymes functioning at the entry points of general phenylpropanoid biosynthesis and flavonoid biosynthesis, respectively. In Arabidopsis, PAL and CHS are turned over through ubiquitination-dependent proteasomal degradation. Specific kelch domain-containing F-Box (KFB) proteins as components of ubiquitin E3 ligase directly interact with PAL or CHS, leading to polyubiquitinated PAL and CHS, which in turn influences phenylpropanoid and flavonoid production. Although phenylpropanoids are vital for tomato nutritional value and stress responses, the post-translational regulation of PAL and CHS in tomato remains unknown. We identified 31 putative KFB-encoding genes in the tomato genome. Our homology analysis and phylogenetic study predicted four PAL-interacting SlKFBs, while SlKFB18 was identified as the sole candidate for the CHS-interacting KFB. Consistent with their homolog function, the predicted four PAL-interacting SlKFBs function in PAL degradation. Surprisingly, SlKFB18 did not interact with tomato CHS and the overexpression or knocking out of SlKFB18 did not affect phenylpropanoid contents in tomato transgenic lines, suggesting its irreverence with flavonoid metabolism. Our study successfully discovered the post-translational regulatory machinery of PALs in tomato while highlighting the limitation of relying solely on a homology-based approach to predict interacting partners of F-box proteins.

Phenylpropanoid metabolism plays an important role in cantaloupe ripening and senescence, but the mechanism of ozone regulation on phenylpropanoid metabolism remains unclear. This study investigated how ozone treatment modulates the levels of secondary metabolites associated with phenylpropanoid metabolism, the related enzyme activities, and gene expression in cantaloupe. Treating cantaloupes with 15 mg/m3 of ozone after precooling can help maintain postharvest hardness. This treatment also enhances the production and accumulation of secondary metabolites, such as total phenols, flavonoids, and lignin. These metabolites are essential components of the phenylpropanoid metabolic pathway, activating enzymes like phenylalanine ammonia-lyase, cinnamate 4-hydroxylase, 4CL, chalcone synthase, and chalcone isomerase. The results of the transcriptional expression patterns showed that differential gene expression related to phenylpropanoid metabolism in the peel of ozone-treated cantaloupes was primarily observed during the middle and late storage stages. In contrast, the pulp exhibited significant differential gene expression mainly during the early storage stage. Furthermore, it was observed that the level of gene expression in the peel was generally higher than that in the pulp. The correlation between the relative amount of gene changes in cantaloupe, activity of selected enzymes, and concentration of secondary metabolites could be accompanied by positive regulation of the phenylpropanoid metabolic pathway. Therefore, ozone stress induction positively enhances the biosynthesis of flavonoids in cantaloupes, leading to an increased accumulation of secondary metabolites. Additionally, it also improves the postharvest storage quality of cantaloupes.

Sprouting can enhance the bioavailability and stimulate the production of health-promoting compounds. This research explored the potential health benefits of wheat sprouting, focusing on underexplored areas in existing literature such as alterations in phenylalanine ammonia-lyase (PAL) activity and glutathione levels during wheat sprouting. Furthermore, special attention was directed toward asparagine (Asn), the main precursor of acrylamide formation, as regulatory agencies are actively seeking to impose limitations on the presence of acrylamide in baked products. The results demonstrate elevated levels of PAL (4.5-fold at 48 h of sprouting), antioxidants, and total phenolics (1.32 mg gallic acid equivalent/g dry matter at 72 h of sprouting), coupled with a reduction in Asn (i.e. 11-fold at 48 h of sprouting) and glutathione concentrations, after wheat sprouting. These findings suggest that sprouting can unlock health-promoting properties in wheat. Optimizing the sprouting process to harness these benefits, however, may have implications for the techno-functionality of wheat flour in food processing.

Phenylalanine ammonia lyase (PAL) is a key enzyme regulating the biosynthesis of the compounds of the phenylpropanoid pathway. This study aimed to isolate and characterize PAL genes from Ferula pseudalliacea Rech.f. (Apiales: Apiaceae) to better understand the regulation of metabolite production. Three PAL gene isoforms (FpPAL1-3) were identified and cloned using the 3\'-RACE technique and confirmed by sequencing. Bioinformatics analysis revealed important structural features, such as phosphorylation sites, physicochemical properties, and evolutionary relationships. Expression analysis by qPCR demonstrated the differential transcription profiles of each FpPAL isoform across roots, stems, leaves, flowers, and seeds. FpPAL1 showed the highest expression in stems, FpPAL2 in roots and flowers, and FpPAL3 in flowers. The presence of three isoforms of PAL in F. pseudalliacea, along with the diversity of PAL genes and their tissue-specific expression profiles, suggests that complex modes of regulation exist for phenylpropanoid biosynthesis in this important medicinal plant. The predicted interaction network revealed associations with key metabolic pathways, emphasizing the multifaceted roles of these PAL genes. In silico biochemical analyses revealed the hydrophilicity of the FpPAL isozyme; however, further analysis of substrate specificity and enzyme kinetics can clarify the specific role of each FpPAL isozyme. These comprehensive results increase the understanding of PAL genes in F. pseudalliacea, helping to characterize their contributions to secondary metabolite biosynthesis.

CONCLUSIONS: DzMYB2 functions as an MYB activator, while DzMYB3 acts as an MYB repressor. They bind to promoters, interact with DzbHLH1, and influence phenolic contents, revealing their roles in phenylpropanoid regulation in durian pulps. Durian fruit has a high nutritional value attributed to its enriched bioactive compounds, including phenolics, carotenoids, and vitamins. While various transcription factors (TFs) regulate phenylpropanoid biosynthesis, MYB (v-myb avian myeloblastosis viral oncogene homolog) TFs have emerged as pivotal players in regulating key genes within this pathway. This study aimed to identify additional candidate MYB TFs from the transcriptome database of the Monthong cultivar at five developmental/postharvest ripening stages. Candidate transcriptional activators were discerned among MYBs upregulated during the ripe stage based on the positive correlation observed between flavonoid biosynthetic genes and flavonoid contents in ripe durian pulps. Conversely, MYBs downregulated during the ripe stage were considered candidate repressors. This study focused on a candidate MYB activator (DzMYB2) and a candidate MYB repressor (DzMYB3) for functional characterization. LC-MS/MS analysis using Nicotiana benthamiana leaves transiently expressing DzMYB2 revealed increased phenolic compound contents compared with those in leaves expressing green fluorescence protein controls, while those transiently expressing DzMYB3 showed decreased phenolic compound contents. Furthermore, it was demonstrated that DzMYB2 controls phenylpropanoid biosynthesis in durian by regulating the promoters of various biosynthetic genes, including phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS), chalcone isomerase (CHI), and dihydroflavonol reductase (DFR). Meanwhile, DzMYB3 regulates the promoters of PAL, 4-coumaroyl-CoA ligase (4CL), CHS, and CHI, resulting in the activation and repression of gene expression. Moreover, it was discovered that DzMYB2 and DzMYB3 could bind to another TF, DzbHLH1, in the regulation of flavonoid biosynthesis. These findings enhance our understanding of the pivotal role of MYB proteins in regulating the phenylpropanoid pathway in durian pulps.

OBJECTIVE: This study aimed to overproduce industrially relevant and safe bio-compound trans-cinnamic acid (tCA) from Photorhabdus luminescens with deletion strategies and homologous expression strategies that had not been applied before for tCA production.
RESULTS: The overproduction of the industrially relevant compound tCA was successfully performed in P. luminescens by deleting stlB (TTO1ΔstlB) encoding a cinnamic acid CoA ligase in the isopropylstilbene pathway and the hcaE insertion (knockout) mutation (hcaE::cat) in the phenylpropionate catabolic pathway, responsible for tCA degradation. A double mutant of both stlB deletion and hcaE insertion mutation (TTO1DM ΔstlB-hcaE::cat) was also generated. These deletion strategies and the phenylalanine ammonium lyase-producing (PI-PAL from Photorhabdus luminescens) plasmid, pBAD30C, carrying stlA (homologous expression mutants) are utilized together in the same strain using different media, a variety of cultivation conditions, and efficient anion exchange resin (Amberlite IRA402) for enhanced tCA synthesis. At the end of the 120-h shake flask cultivation, the maximum tCA production was recorded as 1281 mg l-1 in the TTO1pBAD30C mutant cultivated in TB medium, with the IRA402 resin keeping 793 mg l-1 and the remaining 488 mg l-1 found in the supernatant.
CONCLUSIONS: TCA production was successfully achieved with homologous expression, coupled with deletion and insertion strategies. 1281 mg l-1is the highest tCA concentration that achieved by bacterial tCA production in flask cultivation, according to our knowledge.

Populus pseudo-cathayana × Populus deltoides is a crucial artificial forest tree species in Northeast China. The presence of the fall webworm (Hyphantria cunea) poses a significant threat to these poplar trees, causing substantial economic and ecological damage. This study conducted an insect-feeding experiment with fall webworm on P. pseudo-cathayana × P. deltoides, examining poplar\'s physiological indicators, transcriptome, and metabolome under different lengths of feeding times. Results revealed significant differences in phenylalanine ammonia-lyase activity, total phenolic content, and flavonoids at different feeding durations. Transcriptomic analysis identified numerous differentially expressed genes, including AP2/ERF, MYB, and WRKY transcription factor families exhibiting the highest expression variations. Differential metabolite analysis highlighted flavonoids and phenolic acid compounds of poplar\'s leaves as the most abundant in our insect-feeding experiment. Enrichment analysis revealed significant enrichment in the plant hormone signal transduction and flavonoid biosynthetic pathways. The contents of jasmonic acid and jasmonoyl-L-isoleucine increased with prolonged fall webworm feeding. Furthermore, the accumulation of dihydrokaempferol, catechin, kaempferol, and naringenin in the flavonoid biosynthesis pathway varied significantly among different samples, suggesting their crucial role in response to pest infestation. These findings provide novel insights into how poplar responds to fall webworm infestation.