Molecular phenotyping of the pal1 and pal2 mutants of Arabidopsis thaliana reveals far-reaching consequences on phenylpropanoid, amino acid, and carbohydrate metabolism

Functional redundancy of transcription factors SlNOR and SlNOR-like1 is required for pollen development in tomato

In tomato, SlNOR and SlNOR-like1, members of the NAC family of transcription factors (TFs), are known to play critical roles in regulating fruit ripening and are highly expressed in floral organs. However, their role in flower development remains unclear. In this study, we generated and functionally characterized a double knockout mutant, nor/nor-like1. Our findings reveal that the pollen abortion of the nor/nor-like1 impedes ovarian enlargement, resulting in fruit formation failure. Histological analyses demonstrate that the pollen wall collapse occurs during the mature pollen stage and leads to the abnormal pollen wall component deposition at the microspore stage, resulting in the male sterility in the double knockout mutant lines. Kyoto Encyclopedia of Genes and Genomes enrichment pathway analyses further suggest that the loss of SlNOR and SlNOR-like1 function affects several metabolic pathways related to pollen development, including 'ABC transporters', 'lipid metabolism', 'phenylpropanoid biosynthesis', 'hormone signal transduction', 'starch and sucrose metabolism', and 'cutin, suberine, and wax biosynthesis'. Furthermore, our results demonstrate that SlNOR and SlNOR-like1 could directly bind to the promoters of key genes associated with pollen wall formation and activate their expression, including ATP-binding cassette transporters of the G family (SlABCG8/9/23), ECERIFERUM (SlCER1), and glycine-rich protein (SlGRP92). These findings suggest that SlNOR and SlNOR-like1 may play a redundant role in the biosynthesis and transport of sporopollenin precursors, cuticular wax biosynthesis, and exine formation. In summary, our study highlights a previously uncharacterized role of SlNOR and SlNOR-like1 in tomato pollen wall formation and male fertility.

Polypropylene microplastic exposure modulates multiple metabolic pathways in tobacco leaves, impacting lignin biosynthesis

The adverse effects of microplastics (MPs) and nanoplastics (NPs) on plant growth have gained significant attention. However, the response of tobacco plants to polypropylene microplastics (PP-MPs) remains poorly understood. To address this, a microcosm experiment was conducted in which tobacco seedlings were exposed to PP-MPs at varying concentrations (100 and 1000 mg/kg) and particle sizes (20 nm and 100 µm) for 48 days in red soil. The physicochemical, transcriptomic, and metabolic responses of tobacco plants to PP-MP treatments were assessed. Our findings indicate that the effect of PP-MP exposure on tobacco growth was dose-dependent, with the higher doses (1000 mg/kg) inducing significantly stronger responses. Further, a significant accumulation of key metabolites in the phenylpropanoid and flavonoid biosynthesis pathways such as quercetin, phloretin, kaempferol, liquiritigenin, naringin, myricetin, ferulic acid, formaldehyde, and methyl eugenol was observed in response to PP-MPs. Additionally, the transcriptomic analysis revealed that higher doses enriched more DEGs than lower. KEGG pathway analysis identified significant enrichment in phenylpropanoid biosynthesis, flavonoid biosynthesis, sesquiterpenoid and triterpenoid biosynthesis, and plant hormone signal transduction. The notable variation in the expression of key enzyme-related genes such as PAL, CHI, CSE, C4H, 4CL, COMT, and CYP indicates the substantial impact on lignin synthesis. Lastly, large-sized PPMPs alter the activity of key lignin-degrading enzymes, affecting the lignin content. This study offers valuable insights into the responses of tobacco plants to varying concentrations and sizes of PP-MPs, integrating both physicochemical and molecular perspectives.

Transcriptomics integrated with metabolomics reveals the defense response of insect-resistant Zea mays infested with Spodoptera exigua

Maize (Zea mays) is one of the most important cereal crops worldwide. Insect control through host plant resistance plays an important part in improving both yield and quality of maize. Spodoptera exigua is a common insect pest causing destructive damages to maize. To comprehensively understand molecular mechanism of maize defense against S. exigua, integrated transcriptomics and metabolomics analyses were conducted in the insect-resistant maize inbred line CML139 infested with S. exigua for 24 h. 9845 differentially expressed genes and 34 significantly changed metabolites were identified in infested leaves. Maize transcriptional response to S. exigua infestation involved in genes encoding enzymes in biosynthetic process (ribosome, glycerolipid, glycerophospholipid metabolism), genes in valine, leucine and isoleucine degradation, phenylpropanoid pathway and transcription factors. By metabolism analysis, accumulations of amino acids, organic acids, phenylpropanoids and benzoxazinoids (Bxs) were significantly enhanced, with the exception of salicylic acid (SA) and jasmonic acid (JA). The integrated analysis of transcriptomic and metabolic data demonstrated that both transcripts and metabolites involved in phenylpropanoid and Bxs biosynthesis were differentially modulated in S. exigua infested leaves. This study is valuable in understanding the complex mechanism of interaction between plants and insect herbivores and provide a potential strategy to maize pest control.

Integrating Transcriptomics and Metabolomics to Comprehensively Analyze Phytohormone Regulatory Mechanisms in Rhododendron chrysanthum Pall. Under UV-B Radiation

In order to fully elucidate the roles and systems of phytohormones in UV-B radiation (UV-B) leaves of the Rhododendron chrysanthum Pall. (R. chrysanthum), we conducted a comprehensive analysis of how R. chrysanthum protects itself against UV-B using transcriptomic and metabolomic data. Transcript and metabolite profiles were generated by a combination of deep sequencing and LC-MS/MS (liquid chromatography-tandem mass spectrometry), respectively. Combined with physiological and biochemical assays, we studied compound accumulation, biosynthesis and expression of signaling genes of seven hormones and the effects of hormones on plant photosynthesis. The findings indicate that during leaf defense against UV-B, photosynthesis declined, the photosynthetic system was impaired and the concentration of salicylic acid (SA) hormones increased, whereas the contents of cytokinin (CK), abscisic acid (ABA), ethylene, auxin, jasmonic acid (JA) and gibberellins (GAs) continued to decrease. Finally, correlation tests between hormone content and genes were analyzed, and genes closely related to leaf resistance to UV-B were identified in seven pathways. These results will expand our understanding of the hormonal regulatory mechanisms of plant resistance to UV-B and at the same time lay the foundation for plant resistance to adversity stress.

Mechanisms Involved in Cell Wall Remodeling in Etiolated Rice Shoots Grown Under Osmotic Stress

Osmotic stress impacts the cell wall properties in plants. This study aimed to elucidate the mechanisms involved in cell wall remodeling in etiolated (dark-grown) rice (Oryza sativa L.) shoots grown under polyethylene glycol (PEG)-induced osmotic stress conditions. Shoot growth was inhibited by 70% by the treatment with 60 mM PEG for 2 days. However, when the stressed seedlings were transferred to a solution without PEG, their shoot growth rate increased significantly. A measurement of the cell wall mechanical properties revealed that the cell walls of the stressed shoots became looser and more extensible than those of unstressed shoots. Among the cell wall constituents, the amounts of cell wall-bound phenolic acids, such as ferulic acid (FA), p-coumaric acid (p-CA), and diferulic acid (DFA), per shoot and per unit of matrix polysaccharide content were significantly reduced in the stressed shoots compared to those in the unstressed shoots. Concerning the formation of cell wall-bound phenolic acids, the activity of cell wall-bound peroxidase (CW-PRX) per unit of cell wall content, which is responsible for the coupling reaction of FA to produce DFA, was 3.5 times higher in stressed shoots than in unstressed shoots, while the activity was reduced by 20% on a shoot basis in stressed shoots compared to that in unstressed shoots. The expression levels of the major class III peroxidase genes in stressed shoots were either comparable to or slightly lower than those in unstressed shoots. Conversely, the phenylalanine ammonia-lyase (PAL) activity, which contributes to the biosynthesis of FA and p-CA, was reduced by 55% and 30% on a shoot and unit-of-protein-content basis, respectively, in stressed shoots compared to that in unstressed shoots. The expression levels of abundantly expressed PAL genes decreased by 14-46% under osmotic stress. Moreover, the gene expression levels of specific BAHD acyltransferases, which are responsible for the addition of FA and p-CA to form ester-linked moieties on cell wall constituents, decreased by 15-33% under osmotic stress. These results suggest that the downregulation of the expression of specific PAL and BAHD acyltransferase genes in osmotically stressed rice shoots is responsible for a reduction in the formation of cell wall-bound phenolic acid monomers. This, in turn, may result in a decrease in the levels of DFAs. The reduction in the formation of DFA-mediated cross-linking structures within the cell wall may contribute to an increase in the mechanical extensibility of the cell wall. The remodeling of cell walls in an extensible and loosened state could assist in maintaining the growth capacity of etiolated rice shoots grown under osmotic stress and contribute to rapid growth recovery following the alleviation of osmotic stress.

Genome-wide identification and functional roles relating to anthocyanin biosynthesis analysis in maize

BACKGROUND

Anthocyanin is an important class of water-soluble pigments that are widely distributed in various tissues of plants, and it not only facilitates diverse color changes but also plays important roles in various biological processes. Maize silk, serving as an important reproductive organ and displaying a diverse range of colors, plays an indispensable role in biotic resistance through its possession of anthocyanin. However, the copy numbers, characteristics, and expression patterns of genes involved in maize anthocyanin biosynthesis are not fully understood. In this study, gene numbers, distribution, structure, cis-elements of the anthocyanin synthetic gene family were identified, and then the potential transcriptional factors were predicted by two analyzed methods. Finally, genes involved in maize silk pigment were screened by un-targeted metabolism analysis.

RESULTS

Ten gene families involved in the maize anthocyanin biosynthesis pathway were identified, and 142 synthetic genes were obtained. These anthocyanin biosynthetic genes have high copy numbers and are normally clustered on chromosomes. The promoters of these synthetic genes contain various cis-elements and the gene expression patterns and transcriptional regulatory networks were analyzed. These genes are distributed on different chromosomes and gene expression patterns vary across different tissues in maize. Specifically, these genes often exhibit higher expression in the stem, leaves, and seeds. Ten highly expressed genes in silks were identified. Based on un-targeted metabolites detection in the silks of four maize representative inbred lines with different colors, two main differential anthocyanin components were identified. Furthermore, the gene expression patterns of the ten highly expressed genes and their potential interacting transcriptional factors were analyzed across the four inbred lines.

CONCLUSIONS

The results in this study show a through picture of maize anthocyanin synthetic genes, and the structure and function of genes related to anthocyanin biosynthesis in maize could be further investigated.

RNA-Seq Transcriptomics and iTRAQ Proteomics Analysis Reveal the Dwarfing Mechanism of Blue Fescue (Festuca glauca)

Blue fescue is a widely used ornamental grass because of its strong ecological adaptability. To maintain the optimal ornamental plant shape, blue fescue requires many nutrients and labor. Using dwarf varieties with slow growth is an effective way to fulfill these requirements. In this study, we investigated the dwarfing mechanism of dw-1, a blue fescue dwarfing mutant, using physiological, transcriptomic, and proteomic methods. The peroxidase (POD) enzyme activity and chlorophyll content of dw-1 significantly increased, while the lignin, gibberellin (GA), and indoleacetic acid (IAA) content significantly decreased. A total of 7668 differentially expressed genes (DEGs) were detected using RNA-seq, of which 2543 were upregulated and 5125 were downregulated. A total of 165 differentially expressed proteins (DEPs) were detected using iTRAQ, of which 68 were upregulated and 97 were downregulated. KEGG enrichment analysis showed that the diterpene biosynthesis pathway, tryptophan metabolism pathway, and phenylpropanoid biosynthesis pathway were significantly enriched at both the transcriptional and protein levels. As a result, we can formulate the following hypothesis about the dw-1 dwarfing phenotype: the downregulation of genes and proteins related to IAA and GA biosynthesis is associated with the dwarf phenotype's formation, and metabolic pathways related to lignin synthesis, such as phenylpropanoid biosynthesis, also play an important role. Our work will contribute to a new understanding of the genes and proteins involved in the blue fescue dwarf phenotype.

Bioengineering for robust tolerance against cold and drought stresses via co-overexpressing three Cu-miRNAs in major food crops

Environmental stresses threaten global food security by reducing major crop productivity. MicroRNAs (miRNAs), a class of small non-coding RNAs, function as master regulators of gene expression in plants. In this study, we co-overexpressed three copper-miRNAs (miR397, miR408, and miR528) in three major food crops (referred to as 3miR-OE), which simultaneously silenced several target laccase genes, resulting in reduced lignin contents but increased flavonoid metabolites. Importantly, we observed that, compared to wild-type and single miRNA overexpression lines, the 3miR-OE transgenic Japonica and Indica rice exhibited significantly enhanced tolerance against cold and drought stresses throughout the growth period. In addition, 3miR-OE transgenic maize and wheat also exhibited robust resistance to cold and water-deficit conditions, suggesting that co-overexpressing three Cu-miRNAs is a powerful tool for improving resilience to abiotic stresses across diverse crops. Altogether, we have developed a bioengineering strategy to maintain crop growth and yield under unfavorable environmental conditions.

Foliar application of esculin and digitoxin improve the yield quality of salt-stressed flax by improving the antioxidant defense system

BACKGROUND

Secondary metabolites of several plants, including esculin and digitoxin, which are cardiac glycosides, were previously employed for their therapeutic effects. The current study aims to investigate the functions of the main Na+ /K+ transport inhibitor digitoxin and the antioxidant esculin for enhancing flax plant growth and production under salinity.

METHODOLOGY

Flax plants were irrigated with distilled water supplemented with 0.0 and 5000 mg/L salt solution starting from 15 DAS from sowing. Then exogenous treatment with digitoxin and esculin with 50 mg L- 1 and 100 mg L- 1 were used for this work.

RESULTS

According to the results of this work, foliar spraying of esculin or digitoxin increased the salinity tolerance of flax plants.The foliar application of either esculin or digitoxin induced an elevation in the contents of photosynthetic pigments, osmolytes including soluble sugar and proline as well as the total phenols in salt-stressed flax plants. Moreover, esculin and digitoxin in particular counteract oxidative stress by increasing the activity of antioxidant enzymes including superoxide dismutase, catalase, peroxidase, phenylalanine ammonia-lyase, and tyrosine ammonia lyase, leading to a decrease in reactive oxygen species and lipid peroxidation levels and electrolyte leakage. The efficiency of esculin and digitoxin to sustain ion homeostasis by inhibiting Na+ absorption and increasing potassium, calcium, and phosphorus in flax plants may be the reason for their protective actions towards salinity.As a consequence, esculin and digitoxin increased yield quantity and quality as shown by increases in all investigated yield criteriaas shoot height, root length, their fresh and dry weights as well asseed yield/plant (g), and 1000 seeds weight, especially those that improved the desired oil properties.

CONCLUSION

In conclusion, this study concluded that digitoxin was more effective in inhibiting Na+ build-up and increasing flax salinity tolerance, particularly at the high investigated dose as compared to esculin. In this study, we reported the recent findings of exogenousapplication of either digitoxin or esculin glycosides which are new investigated salt alleviators never used before for improving the salt tolerance in flax plants.

Genome-Wide Characterization and Expression Analysis of CsPALs in Cucumber (Cucumis sativus L.) Reveal Their Potential Roles in Abiotic Stress and Aphid Stress Tolerance

Phenylalanine ammonia lyase (PAL) is a pivotal enzyme in the phenylalanine metabolic pathway in plants and has a crucial role in the plant's response to environmental stress. Although the PAL family has been widely studied in many plant species, limited is known about its particular role in cucumbers under stress. We investigated the physicochemical properties, gene structure, gene duplication events, conserved motifs, cis-acting elements, protein interaction networks, stress-related transcriptome data, and quantitatively validated key stress-related genes. The main results indicated that 15 PAL genes were grouped into four clades: I, II, and III when arranged in a phylogenetic tree of PAL genes in angiosperms. The analysis of the promoter sequence revealed the presence of multiple cis-acting elements related to hormones and stress responses in the cucumber PAL genes (CsPALs). The analysis of protein interaction networks suggested that CsPAL1 interacts with eight other members of the PAL family through CsELI5 and CsHISNA, and directly interacts with multiple proteins in the 4CL family. Further investigation into the expression patterns of CsPAL genes in different tissues and under various stress treatments (NaCl, Cu2+, Zn2+, PEG6000, aphids) demonstrated significant differential expression of CsPALs across cucumber tissues. In summary, our characterization of the CsPAL family offers valuable insights and provides important clues regarding the molecular mechanisms of CsPALs in managing abiotic and biotic stress interactions in cucumbers.

Genes to specialized metabolites: accumulation of scopoletin, umbelliferone and their glycosides in natural populations of Arabidopsis thaliana

BACKGROUND

Scopoletin and umbelliferone belong to coumarins, which are plant specialized metabolites with potent and wide biological activities, the accumulation of which is induced by various environmental stresses. Coumarins have been detected in various plant species, including medicinal plants and the model organism Arabidopsis thaliana. In recent years, key role of coumarins in maintaining iron (Fe) homeostasis in plants has been demonstrated, as well as their significant impact on the rhizosphere microbiome through exudates secreted into the soil environment. Several mechanisms underlying these processes require clarification. Previously, we demonstrated that Arabidopsis is an excellent model for studying genetic variation and molecular basis of coumarin accumulation in plants.

RESULTS

Here, through targeted metabolic profiling and gene expression analysis, the gene-metabolite network of scopoletin and umbelliferone accumulation was examined in more detail in selected Arabidopsis accessions (Col-0, Est-1, Tsu-1) undergoing different culture conditions and characterized by variation in coumarin content. The highest accumulation of coumarins was detected in roots grown in vitro liquid culture. The expression of 10 phenylpropanoid genes (4CL1, 4CL2, 4CL3, CCoAOMT1, C3'H, HCT, F6'H1, F6'H2,CCR1 and CCR2) was assessed by qPCR in three genetic backgrounds, cultured in vitro and in soil, and in two types of tissues (leaves and roots). We not only detected the expected variability in gene expression and coumarin accumulation among Arabidopsis accessions, but also found interesting polymorphisms in the coding sequences of the selected genes through in silico analysis and resequencing.

CONCLUSIONS

To the best of our knowledge, this is the first study comparing accumulation of simple coumarins and expression of phenylpropanoid-related genes in Arabidopsis accessions grown in soil and in liquid cultures. The large variations we detected in the content of coumarins and gene expression are genetically determined, but also tissue and culture dependent. It is particularly important considering that growing plants in liquid media is a widely used technology that provides a large amount of root tissue suitable for metabolomics. Research on differential accumulation of coumarins and related gene expression will be useful in future studies aimed at better understanding the physiological role of coumarins in roots and the surrounding environments.

Suppression of essential oil biosynthesis in sweet basil cotyledons under hypergravity conditions

The mechanism through which gravity influences the biosynthesis of essential oils in herbs is an important issue for plant and space biology. Sweet basil (Ocimum basilicum L.) seedlings were cultivated under centrifugal hypergravity conditions at 100 g in the light, and the growth of cotyledons, development of glandular hairs, and biosynthesis of essential oils were analyzed. The area and fresh weight of the cotyledons increased by similar amounts irrespective of the gravitational conditions. On the abaxial surface of the cotyledons, glandular hairs, where essential oils are synthesized and stored, developed from those with single-cell heads to those with four-cell heads; however, hypergravity did not affect this development. The main components, methyl eugenol and 1,8-cineole, in the essential oils of cotyledons were lower in cotyledons grown under hypergravity conditions. The gene expression of enzymes in the phenylpropanoid pathway involved in the synthesis of methyl eugenol, such as phenylalanine ammonia lyase (PAL) and eugenol O-methyltransferase (EOMT), was downregulated by hypergravity. Hypergravity also decreased the gene expression of enzymes in the 2C-methyl-d-erythritol 4-phosphate (MEP) pathway involved in the synthesis of 1,8-cineole, such as 1-deoxy-d-xylulose-5-phosphate synthase (DXS) and 1,8-cineole synthase (CINS). These results indicate that hypergravity without affecting the development of glandular hairs, decreases the expression of genes related to the biosynthesis of methyl eugenol and 1,8-cineole, which may cause a decrease in the amounts of both essential oils in sweet basil cotyledons.

Identification of tomato F-box proteins functioning in phenylpropanoid metabolism

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.

Pathophysiology and transcriptomic responses of Pinus armandii defenses to ophiostomatoid fungi

Pinus armandii Franch. is an ecologically and economically important evergreen tree species native to western China. Dendroctonus armandi Tsai and Li and pathogenic ophiostomatoid fungi pose substantial threats to P. armandii. With the interplay between species, the defense mechanisms of P. armandii have evolved to withstand external biotic stressors. However, the interactions between P. armandii and pathogenic ophiostomatoid fungal species/strains remain poorly understood. We aimed to analyze the pathophysiological and molecular changes in P. armandii following artificial inoculation with four ophiostomatoid species (Graphilbum parakesiyea, Leptographium qinlingense, Ophiostoma shennongense and Ophiostoma sp. 1). The study revealed that L. qinlingense produced the longest necrotic lesions, and G. parakesiyea produced the shortest. All strains induced monoterpenoid release, and monoterpene levels of P. armandii were positively correlated with fungal virulence (R2 = 0.93, P < 0.01). Co-inoculation of two dominant highly (L. qinlingense) and weakly virulent (O. shennongense) pathogens reduced the pathogenicity of the highly virulent fungi. Transcriptomic analysis of P. armandii (LQ: L. qinlingense treatments, QS: co-inoculation treatments and OS: O. shennongense treatments) showed that the expression pattern of differentially expressed genes (DEGs) between QS and OS was similar, but different from that of LQ. The DEGs (LQ vs QS) involved in flavonoid biosynthesis and phenylpropanoid biosynthesis were downregulated. Notably, compared with LQ, QS significantly decreased the expression of host defense-related genes. This study provides a valuable theoretical basis for managing infestations of D. armandi and associated ophiostomatoid fungi.

A chromosome-scale genome of Rhus chinensis Mill. provides new insights into plant-insect interaction and gallotannins biosynthesis

Rhus chinensis Mill., an economically valuable Anacardiaceae species, is parasitized by the galling aphid Schlechtendalia chinensis, resulting in the formation of the Chinese gallnut (CG). Here, we report a chromosomal-level genome assembly of R. chinensis, with a total size of 389.40 Mb and scaffold N50 of 23.02 Mb. Comparative genomic and transcriptome analysis revealed that the enhanced structure of CG and nutritional metabolism contribute to improving the adaptability of R. chinensis to S. chinensis by supporting CG and galling aphid growth. CG was observed to be abundant in hydrolysable tannins (HT), particularly gallotannin and its isomers. Tandem repeat clusters of dehydroquinate dehydratase/shikimate dehydrogenase (DQD/SDH) and serine carboxypeptidase-like (SCPL) and their homologs involved in HT production were determined as specific to HT-rich species. The functional differentiation of DQD/SDH tandem duplicate genes and the significant contraction in the phenylalanine ammonia-lyase (PAL) gene family contributed to the accumulation of gallic acid and HT while minimizing the production of shikimic acid, flavonoids, and condensed tannins in CG. Furthermore, we identified one UDP glucosyltransferase (UGT84A), three carboxylesterase (CXE), and six SCPL genes from conserved tandem repeat clusters that are involved in gallotannin biosynthesis and hydrolysis in CG. We then constructed a regulatory network of these genes based on co-expression and transcription factor motif analysis. Our findings provide a genomic resource for the exploration of the underlying mechanisms of plant-galling insect interaction and highlight the importance of the functional divergence of tandem duplicate genes in the accumulation of secondary metabolites.

Lignin reduction in sugarcane by performing CRISPR/Cas9 site-direct mutation of SoLIM transcription factor

Genetic engineering of plant cell walls is limited for reducing lignocellulose recalcitrance, so mild and/or green-like pretreatment is still required for sequential enzymatic saccharification. Here, we report a method to reduce lignin content in sugarcane stalks using the CRISPR/Cas 9 technique. Three target sequences of SoLIM were designed and fused to pRGEB32. The cassette constructs were introduced into sugarcane calli cv. KK3 through Agrobacterium-mediated transformation. We produced one base substitution and one insertion line for the 1st target site; two insertions, one deletion, and one base substitution for the 2nd target site; and one base substitution and insertion for the 3rd target site. qRT-PCR analysis of SoLIM, SoPAL, SoC4H, and SoCAD showeded that downregulation of SoLIM by single nucleotide insertions or deletions reduced the expression of SoPAL, SoC4H, and SoCAD. Consequently, the edited lines contained 9.74 to 51.46% less lignin content compared to that in the wild-type plants. The syringyl/guaiacyl (S/G) ratio of the edited lines ranged between 0.23 and 0.49, while the wild-type was 0.22. The histochemical evaluation and scanning electron microscopy of the cell walls supported this observation. A low lignin content sugarcane will provide a better feedstock for second-generation bioethanol production.

Transcriptome Profiles Reveals ScDREB10 from Syntrichia caninervis Regulated Phenylpropanoid Biosynthesis and Starch/Sucrose Metabolism to Enhance Plant Stress Tolerance

Desiccation is a kind of extreme form of drought stress and desiccation tolerance (DT) is an ancient trait of plants that allows them to survive tissue water potentials reaching -100 MPa or lower. ScDREB10 is a DREB A-5 transcription factor gene from a DT moss named Syntrichia caninervis, which has strong comprehensive tolerance to osmotic and salt stresses. This study delves further into the molecular mechanism of ScDREB10 stress tolerance based on the transcriptome data of the overexpression of ScDREB10 in Arabidopsis under control, osmotic and salt treatments. The transcriptional analysis of weight gene co-expression network analysis (WGCNA) showed that "phenylpropanoid biosynthesis" and "starch and sucrose metabolism" were key pathways in the network of cyan and yellow modules. Meanwhile, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis of differentially expressed genes (DEGs) also showed that "phenylpropanoid biosynthesis" and "starch and sucrose metabolism" pathways demonstrate the highest enrichment in response to osmotic and salt stress, respectively. Quantitative real-time PCR (qRT-PCR) results confirmed that most genes related to phenylpropanoid biosynthesis" and "starch and sucrose metabolism" pathways in overexpressing ScDREB10 Arabidopsis were up-regulated in response to osmotic and salt stresses, respectively. In line with the results, the corresponding lignin, sucrose, and trehalose contents and sucrose phosphate synthase activities were also increased in overexpressing ScDREB10 Arabidopsis under osmotic and salt stress treatments. Additionally, cis-acting promoter element analyses and yeast one-hybrid experiments showed that ScDREB10 was not only able to bind with classical cis-elements, such as DRE and TATCCC (MYBST1), but also bind with unknown element CGTCCA. All of these findings suggest that ScDREB10 may regulate plant stress tolerance by effecting phenylpropanoid biosynthesis, and starch and sucrose metabolism pathways. This research provides insights into the molecular mechanisms underpinning ScDREB10-mediated stress tolerance and contributes to deeply understanding the A-5 DREB regulatory mechanism.

Expression profiling of the phenylalanine ammonia-lyase (PAL) gene family in ginkgo biloba L

The PAL gene family plays an important role in plant growth, development, and response to abiotic stresses and has been identified in a variety of plants. However, a systematic characterization is still lacking in Ginkgo biloba. Using a bioinformatics approach, 11 GbPAL members of the PAL gene family identified in ginkgo were identified in this study. The protein structure and physicochemical properties indicated that the GbPAL genes were highly similar. Based on their exon-intron structures, they can be classified into three groups. A total of 62 cis-elements for hormone, light, and abiotic stress responses were identified in the promoters of GbPAL genes, indicating that PAL is a multifunctional gene family. GbPAL genes were specifically expressed in different tissues and ploidy of ginkgo. These results provide a theoretical basis for further studies on the functional expression of the GbPAL genes.

Functional and kinetics of two efficient phenylalanine ammonia lyase from Pyrus bretschneideri

BACKGROUND

The enzyme phenylalanine ammonia lyase (PAL) controls the transition from primary to secondary metabolism by converting L-phenylalanine (L-Phe) to cinnamic acid. However, the function of PAL in pear plants (Pyrus bretschneideri) has not yet been fully elucidated.

RESULTS

We identified three PAL genes (PbPAL1, PbPAL2 and PbPAL3) from the pear genome by exploring pear genome databases. The evolutionary tree revealed that three PbPALs were classified into one group. We expressed PbPAL1 and PbPAL2 recombinant proteins, and the purified PbPAL1 and PbPAL2 proteins showed strict substrate specificity for L-Phe, no activity toward L-Tyr in vitro, and modest changes in kinetics and enzyme characteristics. Furthermore, overexpression of PbAL1 and PbPAL1-RNAi, respectively, and resulted in significant changes in stone cell and lignin contents in pear fruits. The results of yeast one-hybrid (Y1H) assays that PbWLIM1 could bind to the conserved PAL box in the PbPAL promoter and regulate the transcription level of PbPAL2.

CONCLUSIONS

Our findings not only showed PbPAL's potential role in lignin biosynthesis but also laid the foundation for future studies on the regulation of lignin synthesis and stone cell development in pear fruit utilizing molecular biology approaches.

Functional investigation of five R2R3-MYB transcription factors associated with wood development in Eucalyptus using DAP-seq-ML

A multi-tiered transcriptional network regulates xylem differentiation and secondary cell wall (SCW) formation in plants, with evidence of both conserved and lineage-specific SCW network architecture. We aimed to elucidate the roles of selected R2R3-MYB transcription factors (TFs) linked to Eucalyptus wood formation by identifying genome-wide TF binding sites and direct target genes through an improved DAP-seq protocol combined with machine learning for target gene assignment (DAP-seq-ML). We applied this to five TFs including a well-studied SCW master regulator (EgrMYB2; homolog of AtMYB83), a repressor of lignification (EgrMYB1; homolog of AtMYB4), a TF affecting SCW thickness and vessel density (EgrMYB137; homolog of PtrMYB074) and two TFs with unclear roles in SCW regulation (EgrMYB135 and EgrMYB122). Each DAP-seq TF peak set (average 12,613 peaks) was enriched for canonical R2R3-MYB binding motifs. To improve the reliability of target gene assignment to peaks, a random forest classifier was developed from Arabidopsis DAP-seq, RNA-seq, chromatin, and conserved noncoding sequence data which demonstrated significantly higher precision and recall to the baseline method of assigning genes to proximal peaks. EgrMYB1, EgrMYB2 and EgrMYB137 predicted targets showed clear enrichment for SCW-related biological processes. As validation, EgrMYB137 overexpression in transgenic Eucalyptus hairy roots increased xylem lignification, while its dominant repression in transgenic Arabidopsis and Populus reduced xylem lignification, stunted growth, and caused downregulation of SCW genes. EgrMYB137 targets overlapped significantly with those of EgrMYB2, suggesting partial functional redundancy. Our results show that DAP-seq-ML identified biologically relevant R2R3-MYB targets supported by the finding that EgrMYB137 promotes SCW lignification in planta.

Cell-type-specific control of secondary cell wall formation by Musashi-type translational regulators in Arabidopsis

Deciphering the mechanism of secondary cell wall/SCW formation in plants is key to understanding their development and the molecular basis of biomass recalcitrance. Although transcriptional regulation is essential for SCW formation, little is known about the implication of post-transcriptional mechanisms in this process. Here we report that two bonafide RNA-binding proteins homologous to the animal translational regulator Musashi, MSIL2 and MSIL4, function redundantly to control SCW formation in Arabidopsis. MSIL2/4 interactomes are similar and enriched in proteins involved in mRNA binding and translational regulation. MSIL2/4 mutations alter SCW formation in the fibers, leading to a reduction in lignin deposition, and an increase of 4-O-glucuronoxylan methylation. In accordance, quantitative proteomics of stems reveal an overaccumulation of glucuronoxylan biosynthetic machinery, including GXM3, in the msil2/4 mutant stem. We showed that MSIL4 immunoprecipitates GXM mRNAs, suggesting a novel aspect of SCW regulation, linking post-transcriptional control to the regulation of SCW biosynthesis genes.

Developmental Instability and Gene Dysregulation in an Extracted Tetraploid from Hexaploid Wheat

The BBAA subgenomes of hexaploid common wheat can be 'extracted' to constitute a viable and self-reproducing novel tetraploid wheat, termed extracted tetraploid wheat (ETW). Prior studies have shown ETW manifesting phenotypic abnormalities and alteration in gene expression and epigenetic modifications. No population level investigation has been conducted, leaving the issue unclear regarding whether developmental stability, an essential property evolved in all natural organisms, might have been undermined in ETW. Here, we measured variations in five morphological traits and somatic chromosomal stability in populations of ETW and of its hexaploid donor, a resynthesized hexaploid and a natural tetraploid wheat. We observed phenotypic defects in ETW. Meanwhile, we documented much greater within-population variations in ETW than in the other wheat genotypes, most probably due to disrupted developmental stability in ETW. Also, somatic structural chromosome variations were detected only in ETW. Comparative transcriptome analyses indicated that the disrupted developmental stability of ETW is likely linked to massive dysregulation of genome-wide gene expression rather than to genetic mutations. Population network analysis of gene expression implicated intrinsic connectivity among the variable traits, while gene set enrichment analysis provided possible links between dysregulated gene expression and interlaced trait variation.

Blue-green fluorescence during hypersensitive cell death arises from phenylpropanoid deydrodimers

Infection of Arabidopsis with avirulent Pseudomonas syringae and exposure to nitrogen dioxide (NO2) both trigger hypersensitive cell death (HCD) that is characterized by the emission of bright blue-green (BG) autofluorescence under UV illumination. The aim of our current work was to identify the BG fluorescent molecules and scrutinize their biosynthesis, localization, and functions during the HCD. Compared with wild-type (WT) plants, the phenylpropanoid-deficient mutant fah1 developed normal HCD except for the absence of BG fluorescence. Ultrahigh resolution metabolomics combined with mass difference network analysis revealed that WT but not fah1 plants rapidly accumulate dehydrodimers of sinapic acid, sinapoylmalate, 5-hydroxyferulic acid, and 5-hydroxyferuloylmalate during the HCD. FAH1-dependent BG fluorescence appeared exclusively within dying cells of the upper epidermis as detected by microscopy. Saponification released dehydrodimers from cell wall polymers of WT but not fah1 plants. Collectively, our data suggest that HCD induction leads to the formation of free BG fluorescent dehydrodimers from monomeric sinapates and 5-hydroxyferulates. The formed dehydrodimers move from upper epidermis cells into the apoplast where they esterify cell wall polymers. Possible functions of phenylpropanoid dehydrodimers are discussed.

Arogenate dehydratases: unique roles in light-directed development during the seed-to-seedling transition in Arabidopsis thaliana

The seed-to-seedling transition is impacted by changes in nutrient availability and light profiles, but is still poorly understood. Phenylalanine affects early seedling development; thus, the roles of arogenate dehydratases (ADTs), which catalyze phenylalanine formation, were studied in germination and during the seed-to-seedling transition by exploring the impact of light conditions and specific hormone responses in adt mutants of Arabidopsis thaliana. ADT gene expression was assessed in distinct tissues and for light-quality dependence in seedlings for each of the six-member ADT gene family. Mutant adt seedlings were evaluated relative to wild type for germination, photomorphogenesis (blue, red, far red, white light, and dark conditions), anthocyanin accumulation, and plastid development-related phenotypes. ADT proteins are expressed in a light- and tissue-specific manner in transgenic seedlings. Among the analyzed adt mutants, adt3, adt5, and adt6 exhibit significant defects in germination, hypocotyl elongation, and root development responses during the seed-to-seedling transition. Interestingly, adt5 exhibits a light-dependent disruption in plastid development, similar to a phyA mutant. These data indicate interactions between photoreceptors, hormones, and regulation of phenylalanine pools in the process of seedling establishment. ADT5 and ADT6 may play important roles in coordinating hormone and light signals for normal early seedling development.

Non-specific effects of the CINNAMATE-4-HYDROXYLASE inhibitor piperonylic acid

Chemical inhibitors are often implemented for the functional characterization of genes to overcome the limitations associated with genetic approaches. Although it is well established that the specificity of the compound is key to success of a pharmacological approach, off-target effects are often overlooked or simply neglected in a complex biological setting. Here we illustrate the cause and implications of such secondary effects by focusing on piperonylic acid (PA), an inhibitor of CINNAMATE-4-HYDROXYLASE (C4H) that is frequently used to investigate the involvement of lignin during plant growth and development. When supplied to plants, we found that PA is recognized as a substrate by GRETCHEN HAGEN 3.6 (GH3.6), an amido synthetase involved in the formation of the indole-3-acetic acid (IAA) conjugate IAA-Asp. By competing for the same enzyme, PA interferes with IAA conjugation, resulting in an increase in IAA concentrations in the plant. In line with the broad substrate specificity of the GH3 family of enzymes, treatment with PA increased not only IAA levels but also those of other GH3-conjugated phytohormones, namely jasmonic acid and salicylic acid. Finally, we found that interference with the endogenous function of GH3s potentially contributes to phenotypes previously observed upon PA treatment. We conclude that deregulation of phytohormone homeostasis by surrogate occupation of the conjugation machinery in the plant is likely a general phenomenon when using chemical inhibitors. Our results hereby provide a novel and important basis for future reference in studies using chemical inhibitors.

Cotton peroxisome-localized lysophospholipase counteracts the toxic effects of Verticillium dahliae NLP1 and confers wilt resistance

Plasma membrane represents a critical battleground between plants and attacking microbes. Necrosis-and-ethylene-inducing peptide 1 (Nep1)-like proteins (NLPs), cytolytic toxins produced by some bacterial, fungal and oomycete species, are able to target on lipid membranes by binding eudicot plant-specific sphingolipids (glycosylinositol phosphorylceramide) and form transient small pores, causing membrane leakage and subsequent cell death. NLP-producing phytopathogens are a big threat to agriculture worldwide. However, whether there are R proteins/enzymes that counteract the toxicity of NLPs in plants remains largely unknown. Here we show that cotton produces a peroxisome-localized enzyme lysophospholipase, GhLPL2. Upon Verticillium dahliae attack, GhLPL2 accumulates on the membrane and binds to V. dahliae secreted NLP, VdNLP1, to block its contribution to virulence. A higher level of lysophospholipase in cells is required to neutralize VdNLP1 toxicity and induce immunity-related genes expression, meanwhile maintaining normal growth of cotton plants, revealing the role of GhLPL2 protein in balancing resistance to V. dahliae and growth. Intriguingly, GhLPL2 silencing cotton plants also display high resistance to V. dahliae, but show severe dwarfing phenotype and developmental defects, suggesting GhLPL2 is an essential gene in cotton. GhLPL2 silencing results in lysophosphatidylinositol over-accumulation and decreased glycometabolism, leading to a lack of carbon sources required for plants and pathogens to survive. Furthermore, lysophospholipases from several other crops also interact with VdNLP1, implying that blocking NLP virulence by lysophospholipase may be a common strategy in plants. Our work demonstrates that overexpressing lysophospholipase encoding genes have great potential for breeding crops with high resistance against NLP-producing microbial pathogens.

Molecular identification of phenylalanine ammonia lyase-encoding genes EfPALs and EfPAL2-interacting transcription factors in Euryale ferox

Flavonoids are one of the most important secondary metabolites in plants, and phenylalanine ammonia-lyase (PAL) is the first rate-limiting enzyme for their biosynthesis. However, detailed information on the regulation of PAL in plants is still little. In this study, PAL in E. ferox was identified and functionally analyzed, and its upstream regulatory network was investigated. Through genome-wide identification, we obtained 12 putative PAL genes from E. ferox. Phylogenetic tree and synteny analysis revealed that PAL in E. ferox was expanded and mostly preserved. Subsequently, enzyme activity assays demonstrated that EfPAL1 and EfPAL2 both catalyzed the production of cinnamic acid from phenylalanine only, with EfPAL2 exhibiting a superior enzyme activity. Overexpression of EfPAL1 and EfPAL2 in Arabidopsis thaliana, respectively, both enhanced the biosynthesis of flavonoids. Furthermore, two transcription factors, EfZAT11 and EfHY5, were identified by yeast one-hybrid library assays as binding to the promoter of EfPAL2, and further luciferase (LUC) activity analysis indicated that EfZAT11 promoted the expression of EfPAL2, while EfHY5 repressed the expression of EfPAL2. These results suggested that EfZAT11 and EfHY5 positively and negatively regulate flavonoid biosynthesis, respectively. Subcellular localization revealed that EfZAT11 and EfHY5 were localized in the nucleus. Our findings clarified the key EfPAL1 and EfPAL2 of flavonoid biosynthesis in E. ferox and established the upstream regulatory network of EfPAL2, which would provide novel information for the study of flavonoid biosynthesis mechanism.

Transcriptome analysis reveals defense-related genes and pathways during dodder (Cuscuta australis) parasitism on white clover (Trifolium repens)

Dodders (Cuscuta australis R. Br.) are holo-parasitic stem angiosperms with an extensive host range that have significant ecological and economic potential impact on the ecosystem and the agricultural system. However, how the host plant responds to this biotic stress remains mostly unexplored. To identify the defense-related genes and the pathways in white clover (Trifolium repens L.) induced by dodder parasitism, we performed a comparative transcriptome analysis of the leaf and root tissues from white clover with and without dodder infection by high throughput sequencing. We identified 1,329 and 3,271 differentially expressed genes (DEGs) in the leaf and root tissues, respectively. Functional enrichment analysis revealed that plant-pathogen interaction, plant hormone signal transduction, and phenylpropanoid biosynthesis pathways were significantly enriched. Eight WRKY, six AP2/ERF, four bHLH, three bZIP, three MYB, and three NAC transcription factors showed a close relationship with lignin synthesis-related genes, which defended white clover against dodder parasitism. Real-time quantitative PCR (RT-qPCR) for nine DEGs, further validated the data obtained from transcriptome sequencing. Our results provide new insights into understanding the complex regulatory network behind these parasite-host plant interactions.

A reference-grade genome assembly for Astragalus mongholicus and insights into the biosynthesis and high accumulation of triterpenoids and flavonoids in its roots

Astragalus membranaceus var. mongholicus (AMM), a member of the Leguminosae, is one of the most important medicinal plants worldwide. The dried roots of AMM have a wide range of pharmacological effects and are a traditional Chinese medicine. Here, we report the first chromosome-level reference genome of AMM, comprising nine pseudochromosomes with a total size of 1.47 Gb and 27 868 protein-encoding genes. Comparative genomic analysis reveals that AMM has not experienced an independent whole-genome duplication (WGD) event after the WGD event shared by the Papilionoideae species. Analysis of long terminal repeat retrotransposons suggests a recent burst of these elements at approximately 0.13 million years ago, which may explain the large size of the AMM genome. Multiple gene families involved in the biosynthesis of triterpenoids and flavonoids were expanded, and our data indicate that tandem duplication has been the main driver for expansion of these families. Among the expanded families, the phenylalanine ammonia-lyase gene family was primarily expressed in the roots of AMM, suggesting their roles in the biosynthesis of phenylpropanoid compounds. The functional versatility of 2,3-oxidosqualene cyclase genes in cluster III may play a critical role in the diversification of triterpenoids in AMM. Our findings provide novel insights into triterpenoid and flavonoid biosynthesis and can facilitate future research on the genetics and medical applications of AMM.

Transcriptome-based analysis of key pathways relating to yield formation stage of foxtail millet under different drought stress conditions

Although foxtail millet, as small Panicoid crop, is of drought resilient, drought stress has a significant effect on panicle of foxtail millet at the yield formation stage. In this study, the changes of panicle morphology, photosynthesis, antioxidant protective enzyme system, reactive oxygen species (ROS) system, and osmotic regulatory substance and RNA-seq of functional leaves under light drought stress (LD), heavy drought stress (HD), light drought control (LDCK) and heavy drought control (HDCK) were studied to get a snap-shot of specific panicle morphological changes, physiological responses and related molecular mechanisms. The results showed that the length and weight of panicle had decreased, but with increased empty abortive rate, and then yield dropped off 14.9% and 36.9%, respectively. The photosynthesis of millet was significantly decreased, like net photosynthesis rate, stomatal conductance and transpiration rate, especially under HD treatment with reluctant recovery from rehydration. Under LD and HD treatment, the peroxidase (POD) was increased by 34% and 14% and the same as H₂O₂ by 34.7% and 17.2% compared with LDCK and HDCK. The ability to produce and inhibit O^2- free radicals under LD treatment was higher than HD. The content of soluble sugar was higher under LD treatment but the proline was higher under HD treatment. Through RNA-seq analysis, there were 2,393 and 3,078 different genes expressed under LD and HD treatment. According to the correlation analysis between weighted gene coexpression network analysis (WGCNA) and physiological traits, the co-expression network of several modules with high correlation was constructed, and some hub genes of millet in response to drought stress were found. The expression changes relating to carbon fixation, sucrose and starch synthesis, lignin synthesis, gibberellin synthesis, and proline synthesis of millet were specifically analyzed. These findings provide a full perspective on how drought affects the yield formation of foxtail millet by constructing one work model thereby providing theoretical foundation for hub genes exploration and drought resistance breeding of foxtail millet.

OsPPR11 encoding P-type PPR protein that affects group II intron splicing and chloroplast development

OsPPR11 belongs to the P-type PPR protein family and can interact with OsCAF2 to regulate Group II intron splicing and affect chloroplast development in rice. Pentatricopeptide repeat (PPR) proteins participate in chloroplasts or mitochondria group II introns splicing in plants. The PPR protein family contains 491 members in rice, but most of their functions are unknown. In this study, we identified a nuclear gene encoding the P-type PPR protein OsPPR11 in chloroplasts. The qRT-PCR analysis demonstrated that OsPPR11 was expressed in all plant tissues, but leaves had the highest expression. The osppr11 mutants had yellowing leaves and a lethal phenotype that inhibited chloroplast development and photosynthesis-related gene expression and reduced photosynthesis-related protein accumulation in seedlings. Moreover, photosynthetic complex accumulation decreased significantly in osppr11 mutants. The OsPPR11 is required for ndhA, and ycf3-1 introns splicing and interact with CRM family protein OsCAF2, suggesting that these two proteins may form splicing complexes to regulate group II introns splicing. Further analysis revealed that OsCAF2 interacts with OsPPR11 through the N-terminus. These results indicate that OsPPR11 is essential for chloroplast development and function by affecting group II intron splicing in rice.

A tracking work on how Sm4CL2 re-directed the biosynthesis of salvianolic acids and tanshinones in Salvia miltiorrhiza hairy roots

Overexpression and antisense expression of Sm4CL2 re-directed the biosynthesis of salvianolic acids and tanshinones in Salvia miltiorrhiza hairy roots. Danshen (Salvia miltiorrhiza Bunge) is a widely used traditional Chinese medicine and its main active ingredients are water-soluble phenolic acids and lipophilic diterpenoids which are produced through the phenylpropanoid pathway and terpenoid pathway, respectively. 4-Coumaric acid: Coenzyme A ligase (4CL) is a key enzyme in the phenylpropanoid metabolism. We had obtained Sm4CL2-overexpressing (Sm4CL2-OE) and antisense Sm4CL2-expressing (anti-Sm4CL2) danshen hairy roots over ten years ago. In the follow-up study, we found that total salvianolic acids in Sm4CL2-OE-4 hairy roots increased to 1.35 times of the control-3, and that in anti-Sm4CL2-1 hairy roots decreased to 37.32% of the control-3, but tanshinones in anti-Sm4CL2-1 was accumulated to 1.77 ± 0.16 mg/g of dry weight, compared to undetectable in Sm4CL2-OE-4 and the control-3 hairy roots. Interestingly, Sm4CL2-OE-4 hairy roots contained more lignin, 1.36 times of the control-3, and enhanced cell wall and xylem lignification. Transcriptomic analysis revealed that overexpression of Sm4CL2 caused the upregulation of other phenylpropanoid pathway genes and antisense Sm4CL2 expression resulted in the downregulation of other phenylpropanoid pathway genes but activated the expression of terpenoid pathway genes like SmCYP76AK5, SmGPPS.SSUII.1 and SmDXS2. Protein-protein interaction analysis suggested that Sm4CL2 might interact with PAL, PAL4, CSE, CCoAOMT and SmCYP84A60, and appeared to play a key role in the interaction network. The tracking work in this study proved that Sm4CL2 could redirect both salvianolic acids and tanshinones biosynthesis possibly through synergistically regulating other pathway genes. It also indicated that genetic modification of plant secondary metabolism with biosynthetic gene might cause other responses through protein-protein interactions.

Blue Light Regulates Cell Wall Structure and Carbohydrate Metabolism of Soybean Hypocotyl

Soybean stem elongation and thickening are related to cell wall composition. Plant morphogenesis can be influenced by blue light, which can regulate cell wall structure and composition, and affect stem growth and development. Here, using proteomics and metabolomics, differentially expressed proteins and metabolites of hypocotyls grown in the dark and under blue light were studied to clarify the effects of blue light on the cell wall structure and carbohydrate metabolism pathway of soybean hypocotyls. Results showed that 1120 differential proteins were upregulated and 797 differential proteins were downregulated under blue light treatment, while 63 differential metabolites were upregulated and 36 differential metabolites were downregulated. Blue light promoted the establishment of cell wall structure and composition by regulating the expression of both the enzymes and metabolites related to cell wall structural composition and nonstructural carbohydrates. Thus, under blue light, the cross-sectional area of the hypocotyl and xylem were larger, the longitudinal length of pith cells was smaller, elongation of the soybean hypocotyl was inhibited, and diameter was increased.

Modulation of lignin biosynthesis for drought tolerance in plants

Lignin is a complex polymer that is embedded in plant cell walls to provide physical support and water protection. For these reasons, the production of lignin is closely linked with plant adaptation to terrestrial regions. In response to developmental cues and external environmental conditions, plants use an elaborate regulatory network to determine the timing and location of lignin biosynthesis. In this review, we summarize the canonical lignin biosynthetic pathway and transcriptional regulatory network of lignin biosynthesis, consisting of NAC and MYB transcription factors, to explain how plants regulate lignin deposition under drought stress. Moreover, we discuss how the transcriptional network can be applied to the development of drought tolerant plants.

Genome-wide studies of PAL genes in sorghum and their responses to aphid infestation

Phenylalanine ammonia-lyase (PAL, EC 4.3.1.25) plays a crucial role in plant adaptation to biotic and abiotic stresses. However, the current knowledge about PAL proteins in sorghum is essentially lacking. Thus, in this study we aimed to analyze the PAL family genes in sorghum using a genome-wide approach and to explore the role of PAL genes in host plant resistance to aphids via SA-mediated defense signaling. Here, we report gene structural features of 8 PAL (SbPAL) genes in sorghum (Sorghum bicolor), their phylogeny, protein motifs and promoter analysis. Furthermore, we demonstrated that the SbPAL genes were induced by sugarcane aphid (SCA) infestation and SbPAL exhibited differential gene expression in susceptible and resistant genotypes. PAL activity assays further validated upregulated expression of the SbPAL genes in a resistant genotype. In addition, exogenous application of SA reduced plant damage and suppressed aphid population growth and fecundity in susceptible genotype, suggesting that those SbPAL genes act as positive regulator of the SA-mediated defense signaling pathway to combat aphid pests in sorghum. This study provides insights for further examination of the defense role of PAL in sorghum against other pests and pathogens.

Transcriptomic and metabolomic analyses reveal the mechanism of uniconazole inducing hypocotyl dwarfing by suppressing BrbZIP39-BrPAL4 module mediating lignin biosynthesis in flowering Chinese cabbage

Uniconazole, a triazole plant growth regulator, is widely used to regulate plant height and prevent the overgrowth of seedlings. However, the underlying molecular mechanism of uniconazole in inhibiting the hypocotyl elongation of seedlings is still largely unclear, and there has been little research on the integration of transcriptomic and metabolomic data to investigate the mechanisms of hypocotyl elonga-tion. Herein we observed that the hypocotyl elongation of flowering Chinese cabbage seedings was significantly inhibited by uniconazole. Interestingly, based on combined transcriptome and metabolome analyses, we found that the "phenylpropanoid biosynthesis" pathway was significantly affected by uniconazole. In this pathway, only one member of the portal enzyme gene family, named BrPAL4, was remarkably downregulated, which was related to lignin biosynthesis. Furthermore, the yeast one-hybrid and dual-luciferase assays showed that BrbZIP39 could directly bind to the promoter region of BrPAL4 and activate its transcript. The virus-induced gene silencing system further demonstrated that BrbZIP39 could positively regulate hypocotyl elongation and the lignin biosynthesis of hypocotyl. Our findings provide a novel insight into the molecular regulatory mechanism of uniconazole inhibiting hypocotyl elongation in flowering Chinese cabbage and confirm, for the first time, that uniconazole decreases lignin content through repressing the BrbZIP39-BrPAL4 module-mediated phenylpropanoid biosynthesis, which leads to the hypocotyl dwarfing of flowering Chinese cabbage seedlings.

Transcript and metabolite network perturbations in lignin biosynthetic mutants of Arabidopsis

Lignin, one of the most abundant polymers in plants, is derived from the phenylpropanoid pathway, which also gives rise to an array of metabolites that are essential for plant fitness. Genetic engineering of lignification can cause drastic changes in transcription and metabolite accumulation with or without an accompanying development phenotype. To understand the impact of lignin perturbation, we analyzed transcriptome and metabolite data from the rapidly lignifying stem tissue in 13 selected phenylpropanoid mutants and wild-type Arabidopsis (Arabidopsis thaliana). Our dataset contains 20,974 expressed genes, of which over 26% had altered transcript levels in at least one mutant, and 18 targeted metabolites, all of which displayed altered accumulation in at least one mutant. We found that lignin biosynthesis and phenylalanine supply via the shikimate pathway are tightly co-regulated at the transcriptional level. The hierarchical clustering analysis of differentially expressed genes (DEGs) grouped the 13 mutants into 5 subgroups with similar profiles of mis-regulated genes. Functional analysis of the DEGs in these mutants and correlation between gene expression and metabolite accumulation revealed system-wide effects on transcripts involved in multiple biological processes.

Phenylalanine Ammonia Lyase GmPAL1.1 Promotes Seed Vigor under High-Temperature and -Humidity Stress and Enhances Seed Germination under Salt and Drought Stress in Transgenic Arabidopsis

Seed vigor is an important agronomic attribute, essentially associated with crop yield. High-temperature and humidity (HTH) stress directly affects seed development of plants, resulting in the decrease of seed vigor. Therefore, it is particularly important to discover HTH-tolerant genes related to seed vigor. Phenylalanine ammonia lyase (PAL, EC 4.3.1.24) is the first rate-limiting enzyme in the phenylpropanoid biosynthesis pathway and a key enzyme involved in plant growth and development and environmental adaptation. However, the biological function of PAL in seed vigor remains unknown. Here, GmPAL1.1 was cloned from soybean, and its protein was located in the cytoplasm and cell membrane. GmPAL1.1 was significantly induced by HTH stress in developing seeds. The overexpression of GmPAL1.1 in Arabidopsis (OE) accumulated lower level of ROS in the developing seeds and in the leaves than the WT at the physiological maturity stage under HTH stress, and the activities of SOD, POD, and CAT and flavonoid contents were significantly increased, while MDA production was markedly reduced in the leaves of the OE lines than in those of the WT. The germination rate and viability of mature seeds of the OE lines harvested after HTH stress were higher than those of the WT. Compared to the control, the overexpression of GmPAL1.1 in Arabidopsis enhanced the tolerance to salt and drought stresses during germination. Our results suggested the overexpression of GmPAL1.1 in Arabidopsis promoted seed vigor at the physiological maturation period under HTH stress and increased the seeds' tolerance to salt and drought during germination.

Genetic Characterization of Some Saudi Arabia's Accessions from Commiphora gileadensis Using Physio-Biochemical Parameters, Molecular Markers, DNA Barcoding Analysis and Relative Gene Expression

Commiphora gileadensis L. is a medicinal plant, known as balsam, with pharmaceutical potential for its phytochemical activities and chemical constituents. Genetic diversity is a genetic tool used in medicinal plant evolution and conservation. Three accessions from C. gileadensis were collected from three localities in Saudi Arabia (Jeddah, Jizan and Riyadh). Genetic characterization was carried out using physio-biochemical parameters, molecular markers (inter-simple sequence repeat (ISSR) and start codon targeted (SCoT)), DNA barcoding (18 S rRNA and ITS rDNA regions), relative gene expressions (phenylalanine ammonia-lyase 1 (PAL1), defensin (PR-12)) and pathogenesis-related protein (AFPRT). The results of this study showed that C. gileadensis accession C3, collected from Riyadh, had the highest content from the physio-biochemical parameters perspective, with values of 92.54 mg/g and 77.13 mg/g for total phenolic content (TPC) and total flavonoid content (TFC), respectively. Furthermore, the highest content of antioxidant enzyme activity was present in accession C3 with values of 16.87, 60.87, 35.76 and 27.98 U mg-1 for superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) (mol/min/mg FW) and ascorbate peroxidase (APX) (U mg-1 protein), respectively. The highest total number of bands and number of unique bands were 138 and 59, respectively, for the SCoT marker. The SCoT marker was the most efficient for the genetic diversity of C. gileadensis by producing the highest polymorphism (75.63%). DNA barcoding using 18 S and ITS showed the nearby Commiphora genus and clustered C. gileadensis accessions from Jeddah and Jizan in one clade and the C. gileadensis accession from Ryiadh in a separate cluster. Moreover, relative gene expression of the PAL1, defensin (PR-12) and AFPRT (PR1) genes was upregulated in the C. gileadensis accession from Ryiadh. In conclusion, ecological and environmental conditions in each locality affect the genomic expression and genetic diversity, which can help the evolution of important medicinal plants and improve breeding and conservation systems.

Transcriptional and metabolic changes associated with internode development and reduced cinnamyl alcohol dehydrogenase activity in sorghum

The molecular mechanisms associated with secondary cell wall (SCW) deposition in sorghum remain largely uncharacterized. Here, we employed untargeted metabolomics and large-scale transcriptomics to correlate changes in SCW deposition with variation in global gene expression profiles and metabolite abundance along an elongating internode of sorghum, with a major focus on lignin and phenolic metabolism. To gain deeper insight into the metabolic and transcriptional changes associated with pathway perturbations, a bmr6 mutant [with reduced cinnamyl alcohol dehydrogenase (CAD) activity] was analyzed. In the wild type, internode development was accompanied by an increase in the content of oligolignols, p-hydroxybenzaldehyde, hydroxycinnamate esters, and flavonoid glucosides, including tricin derivatives. We further identified modules of genes whose expression pattern correlated with SCW deposition and the accumulation of these target metabolites. Reduced CAD activity resulted in the accumulation of hexosylated forms of hydroxycinnamates (and their derivatives), hydroxycinnamaldehydes, and benzenoids. The expression of genes belonging to one specific module in our co-expression analysis correlated with the differential accumulation of these compounds and contributed to explaining this metabolic phenotype. Metabolomics and transcriptomics data further suggested that CAD perturbation activates distinct detoxification routes in sorghum internodes. Our systems biology approach provides a landscape of the metabolic and transcriptional changes associated with internode development and with reduced CAD activity in sorghum.

High temperature increased lignin contents of poplar (Populus spp) stem via inducing the synthesis caffeate and coniferaldehyde

Lignin contributes to plant resistance to biotic and abiotic stresses and is dominantly regulated by enzymes which catalyze the generation of metabolites intermediates in lignin synthesis. However, the response of lignin and its key regulatory factors to high temperature stress are poorly understood. Here, this finding revealed that the content of lignin in poplar (Populus spp) stem increased after 3 days of high temperature stress treatment. In fourteen metabolic intermediates of lignin biosynthetic pathway with targeted metabolomics analysis, caffeate and coniferaldehyde increased evidently upon heat stress. C3’H (p-Coumaroylshikimate 3-hydroxylase) and CCR (Cinnamoyl-CoA reductase) are recognized to catalyze the formation of caffeate and coniferaldehyde, respectively. Transcriptome data and RT-qPCR (reverse transcription-quantitative real-time polymerase chain reaction) analysis uncovered the high transcriptional level of PtrMYBs (PtrMYB021, PtrMYB074, PtrMYB85, PtrMYB46), PtrC3’H1 (Potri.006G033300) and PtrCCR2 (Potri.003G181400), suggesting that they played the vital role in the increase of lignin and its metabolic intermediates were induced by high temperature. The discovery of key regulators and metabolic intermediates in lignin pathway that respond to high temperature provides a theoretical basis for quality improvement of lignin and the application of forest resources.

Bruceine D may affect the phenylpropanoid biosynthesis by acting on ADTs thus inhibiting Bidens pilosa L. seed germination

Bruceine D is a natural quassinoid, which was successfully isolated in our research group from the residue of Brucea javanica (L.) seeds. Our previous research showed that Bruceine D prevented Bidens pilosa L. seed germination by suppressing the activity of key enzymes and the expression levels of key genes involved in the phenylpropanoid biosynthesis pathway. In this study, integrated analyses of non-targeted metabolomic and transcriptomic were performed. A total of 356 different accumulated metabolites (DAMs) were identified, and KEGG pathway analyses revealed that most of these DAMs were involved in phenylpropanoid biosynthesis. The decreased expression of ADTs and content of L-phenylalanine implicates that Bruceine D may suppress the downstream phenylpropanoid biosynthesis pathway by disrupting primary metabolism, that is, the phenylalanine biosynthesis pathway, thus inhibiting the final products, resulting in the interruption of B. pilosa seed germination. These results suggest that Bruceine D may inhibit the B. pilosa seed germination by suppressing phenylpropanoid biosynthesis through acting on ADTs.

Proteomic and metabolic disturbances in lignin-modified Brachypodium distachyon

Lignin biosynthesis begins with the deamination of phenylalanine and tyrosine (Tyr) as a key branch point between primary and secondary metabolism in land plants. Here, we used a systems biology approach to investigate the global metabolic responses to lignin pathway perturbations in the model grass Brachypodium distachyon. We identified the lignin biosynthetic protein families and found that ammonia-lyases (ALs) are among the most abundant proteins in lignifying tissues in grasses. Integrated metabolomic and proteomic data support a link between lignin biosynthesis and primary metabolism mediated by the ammonia released from ALs that is recycled for the synthesis of amino acids via glutamine. RNA interference knockdown of lignin genes confirmed that the route of the canonical pathway using shikimate ester intermediates is not essential for lignin formation in Brachypodium, and there is an alternative pathway from Tyr via sinapic acid for the synthesis of syringyl lignin involving yet uncharacterized enzymatic steps. Our findings support a model in which plant ALs play a central role in coordinating the allocation of carbon for lignin synthesis and the nitrogen available for plant growth. Collectively, these data also emphasize the value of integrative multiomic analyses to advance our understanding of plant metabolism.

Phenylalanine suppresses cell death caused by loss of fumarylacetoacetate hydrolase in Arabidopsis

Fumarylacetoacetate hydrolase (FAH) catalyzes the final step of Tyrosine (Tyr) degradation pathway essential to animals and the deficiency of FAH causes an inborn lethal disease. In plants, a role of this pathway was unknown until we found that mutation of Short-day Sensitive Cell Death1 (SSCD1), encoding Arabidopsis FAH, results in cell death under short day. Phenylalanine (Phe) could be converted to Tyr and then degraded in both animals and plants. Phe ingestion in animals worsens the disease caused by FAH defect. However, in this study we found that Phe represses cell death caused by FAH defect in plants. Phe treatment promoted chlorophyll biosynthesis and suppressed the up-regulation of reactive oxygen species marker genes in the sscd1 mutant. Furthermore, the repression of sscd1 cell death by Phe could be reduced by α-aminooxi-β-phenylpropionic acid but increased by methyl jasmonate, which inhibits or activates Phe ammonia-lyase catalyzing the first step of phenylpropanoid pathway, respectively. In addition, we found that jasmonate signaling up-regulates Phe ammonia-lyase 1 and mediates the methyl jasmonate enhanced repression of sscd1 cell death by Phe. These results uncovered the relation between chlorophyll biosynthesis, phenylpropanoid pathway and jasmonate signaling in regulating the cell death resulting from loss of FAH in plants.

The Kelch-F-box protein SMALL AND GLOSSY LEAVES 1 (SAGL1) negatively influences salicylic acid biosynthesis in Arabidopsis thaliana by promoting the turn-over of transcription factor SYSTEMIC ACQUIRED RESISTANCE DEFICIENT 1 (SARD1)

Salicylic acid (SA) is a key phytohormone regulating plant immunity. Although the transcriptional regulation of SA biosynthesis has been well-studied, its post-translational regulation is largely unknown. We report that a Kelch repeats-containing F-box (KFB) protein, SMALL AND GLOSSY LEAVES 1 (SAGL1), negatively influences SA biosynthesis in Arabidopsis thaliana by mediating the proteolytic turnover of SYSTEMIC ACQUIRED RESISTANCE DEFICIENT 1 (SARD1), a master transcription factor that directly drives SA biosynthesis during immunity. Loss of SAGL1 resulted in characteristic growth inhibition. Combining metabolomic, transcriptional and phenotypic analyses, we found that SAGL1 represses SA biosynthesis and SA-mediated immune activation. Genetic crosses to mutants that are deficient in SA biosynthesis blocked the SA overaccumulation in sagl1 and rescued its growth. Biochemical and proteomic analysis identified that SAGL1 interacts with SARD1 and promotes the degradation of SARD1 in a proteasome-dependent manner. These results unravelled a critical role of KFB protein SAGL1 in maintaining SA homeostasis via controlling SARD1 stability.

Characteristics and candidate genes associated with excellent stalk strength in maize (Zea mays L.)

Lodging is a major problem in maize production, which seriously affects yield and hinders mechanized harvesting. Improving stalk strength is an effective way to improve lodging. The maize inbred line Jing2416 (J2416) was an elite germplasm in maize breeding which had strong stalk mechanical strength. To explore the characteristics its stalk strength, we conducted physiological, metabolic and transcriptomic analyses of J2416 and its parents Jing24 (J24) and 5237. At the kernel dent stage, the stalk rind penetrometer strength of J2416 was significantly higher than those of its two parents in multiple environments. The rind thickness, sclerenchyma tissue thickness, and cellulose, hemicellulose, and lignin contents of J2416 were significantly higher than those of its parents. Based on the significant differences between J2416 and 5237, we detected metabolites and gene transcripts showing differences in abundance between these two materials. A total of 212 (68.60%) metabolites and 2287 (43.34%) genes were up-regulated in J2416 compared with 5237. The phenylpropanoid and glycan synthesis/metabolism pathways were enriched in metabolites and genes that were up-regulated in J2416. Twenty-eight of the up-regulated genes in J2416 were involved in lignin, cellulose, and hemicellulose synthesis pathways. These analyses have revealed important physiological characteristics and candidate genes that will be useful for research and breeding of inbred lines with excellent stalk strength.

Recent advances in proteomics and metabolomics in plants

Over the past decade, systems biology and plant-omics have increasingly become the main stream in plant biology research. New developments in mass spectrometry and bioinformatics tools, and methodological schema to integrate multi-omics data have leveraged recent advances in proteomics and metabolomics. These progresses are driving a rapid evolution in the field of plant research, greatly facilitating our understanding of the mechanistic aspects of plant metabolisms and the interactions of plants with their external environment. Here, we review the recent progresses in MS-based proteomics and metabolomics tools and workflows with a special focus on their applications to plant biology research using several case studies related to mechanistic understanding of stress response, gene/protein function characterization, metabolic and signaling pathways exploration, and natural product discovery. We also present a projection concerning future perspectives in MS-based proteomics and metabolomics development including their applications to and challenges for system biology. This review is intended to provide readers with an overview of how advanced MS technology, and integrated application of proteomics and metabolomics can be used to advance plant system biology research.

Pivotal Role of Phytohormones and Their Responsive Genes in Plant Growth and Their Signaling and Transduction Pathway under Salt Stress in Cotton

The presence of phyto-hormones in plants at relatively low concentrations plays an indispensable role in regulating crop growth and yield. Salt stress is one of the major abiotic stresses limiting cotton production. It has been reported that exogenous phyto-hormones are involved in various plant defense systems against salt stress. Recently, different studies revealed the pivotal performance of hormones in regulating cotton growth and yield. However, a comprehensive understanding of these exogenous hormones, which regulate cotton growth and yield under salt stress, is lacking. In this review, we focused on new advances in elucidating the roles of exogenous hormones (gibberellin (GA) and salicylic acid (SA)) and their signaling and transduction pathways and the cross-talk between GA and SA in regulating crop growth and development under salt stress. In this review, we not only focused on the role of phyto-hormones but also identified the roles of GA and SA responsive genes to salt stress. Our aim is to provide a comprehensive review of the performance of GA and SA and their responsive genes under salt stress, assisting in the further elucidation of the mechanism that plant hormones use to regulate growth and yield under salt stress.

Genome-Wide Analysis and Expression Profiling of the Phenylalanine Ammonia-Lyase Gene Family in Solanum tuberosum

Phenylalanine ammonia-lyase is one of the most widely studied enzymes in the plant kingdom. It is a crucial pathway from primary metabolism to significant secondary phenylpropanoid metabolism in plants, and plays an essential role in plant growth, development, and stress defense. Although PAL has been studied in many actual plants, only one report has been reported on potato, one of the five primary staple foods in the world. In this study, 14 StPAL genes were identified in potato for the first time using a genome-wide bioinformatics analysis, and the expression patterns of these genes were further investigated using qRT-PCR. The results showed that the expressions of StPAL1, StPAL6, StPAL8, StPAL12, and StPAL13 were significantly up-regulated under drought and high temperature stress, indicating that they may be involved in the stress defense of potato against high temperature and drought. The expressions of StPAL1, StPAL2, and StPAL6 were significantly up-regulated after MeJa hormone treatment, indicating that these genes are involved in potato chemical defense mechanisms. These three stresses significantly inhibited the expression of StPAL7, StPAL10, and StPAL11, again proving that PAL is a multifunctional gene family, which may give plants resistance to multiple and different stresses. In the future, people may improve critical agronomic traits of crops by introducing other PAL genes. This study aims to deepen the understanding of the versatility of the PAL gene family and provide a valuable reference for further genetic improvement of the potato.