A metabolomic assessment of NAC154 transcription factor overexpression in field grown poplar stem wood

The transcriptional regulation of a putative hemicellulose gene, PtrPARVUS2 in poplar

The plant cell wall serves as a critical interface between the plant and its environment, offering protection against various stresses and contributing to biomass production. Hemicellulose is one of the major components of the cell wall, and understanding the transcriptional regulation of its production is essential to fully understanding cell wall formation. This study explores the regulatory mechanisms underlying one of the genes involved in hemicellulose biosynthesis, PtrPARVUS2. Six transcription factors (TFs) were identified from a xylem-biased library to negatively regulate PtrPARVUS2 expression. These TFs, belonging to diverse TF families, were confirmed to bind to specific cis-elements in the PtrPARVUS2 promoter region, as validated by Yeast One-Hybrid (Y1H) assays, transient expression analysis, and Chromatin Immunoprecipitation sequencing (ChIP-seq) assays. Furthermore, motif analysis identified putative cis-regulatory elements bound by these TFs, shedding light on the transcriptional regulation of SCW biosynthesis genes. Notably, several TFs targeted genes encoding uridine diphosphate glycosyltransferases (UGTs), crucial enzymes involved in hemicellulose glycosylation. Phylogenetic analysis of UGTs regulated by these TFs highlighted their diverse roles in modulating hemicellulose synthesis. Overall, this study identifies a set of TFs that regulate PARVUS2 in poplar, providing insights into the intricate coordination of TFs and PtrPARVUS2 in SCW formation. Understanding these regulatory mechanisms enhances our ability to engineer plant biomass for tailored applications, including biofuel production and bioproduct development.

Integrated mass spectrometry imaging and single-cell transcriptome atlas strategies provide novel insights into taxoid biosynthesis and transport in Taxus mairei stems

Taxol, which is a widely used important chemotherapeutic agent, was originally isolated from Taxus stem barks. However, little is known about the precise distribution of taxoids and the transcriptional regulation of taxoid biosynthesis across Taxus stems. Here, we used MALDI-IMS analysis to visualize the taxoid distribution across Taxus mairei stems and single-cell RNA sequencing to generate expression profiles. A single-cell T. mairei stem atlas was created, providing a spatial distribution pattern of Taxus stem cells. Cells were reordered using a main developmental pseudotime trajectory which provided temporal distribution patterns in Taxus stem cells. Most known taxol biosynthesis-related genes were primarily expressed in epidermal, endodermal, and xylem parenchyma cells, which caused an uneven taxoid distribution across T. mairei stems. We developed a single-cell strategy to screen novel transcription factors (TFs) involved in taxol biosynthesis regulation. Several TF genes, such as endodermal cell-specific MYB47 and xylem parenchyma cell-specific NAC2 and bHLH68, were implicated as potential regulators of taxol biosynthesis. Furthermore, an ATP-binding cassette family transporter gene, ABCG2, was proposed as a potential taxoid transporter candidate. In summary, we generated a single-cell Taxus stem metabolic atlas and identified molecular mechanisms underpinning the cell-specific transcriptional regulation of the taxol biosynthesis pathway.

Genome-Wide Identification of Long Noncoding RNAs and Their Responses to Salt Stress in Two Closely Related Poplars

Long noncoding RNAs (lncRNAs) are involved in various biological regulatory processes, but their roles in plants resistance to salt stress remain largely unknown. To systematically explore the characteristics of lncRNAs and their roles in plant salt responses, we conducted strand-specific RNA-sequencing of four tissue types with salt treatments in two closely related poplars (Populus euphratica and Populus alba var. pyramidalis), and a total of 10,646 and 10,531 lncRNAs were identified, respectively. These lncRNAs showed significantly lower values in terms of length, expression, and expression correction than with mRNA. We further found that about 40% and 60% of these identified lncRNAs responded to salt stress with tissue-specific expression patterns across the two poplars. Furthermore, lncRNAs showed weak evolutionary conservation in sequences and exhibited diverse regulatory styles; in particular, tissue- and species-specific responses to salt stress varied greatly in two poplars, for example, 322 lncRNAs were found highly expressed in P. euphratica but not in P. alba var. pyramidalis and 3,425 lncRNAs were identified to be species-specific in P. euphratica in response to salt stress. Moreover, tissue-specific expression of lncRNAs in two poplars were identified with predicted target genes included Aux/IAA, NAC, MYB, involved in regulating plant growth and the plant stress response. Taken together, the systematic analysis of lncRNAs between sister species enhances our understanding of the characteristics of lncRNAs and their roles in plant growth and salt response.

Comparative Metabolomic Analysis of the Cambium Tissue of Non-transgenic and Multi-Gene Transgenic Poplar (Populus × euramericana 'Guariento')

Poplar, a model for woody plant research, is the most widely distributed tree species in the world. Metabolites are the basis of phenotypes, allowing an intuitive and effective understanding of biological processes and their mechanisms. However, metabolites in non-transgenic and multi-gene transgenic poplar remains poorly characterized, especially in regards of the influences on quantity and in the analysis of the relative abundance of metabolites after the introduction of multi stress-related genes. In this study, we investigated the cambium metabolomes of one non-transgenic (D5-0) and two multi-gene (vgb, SacB, ERF36, BtCry3A, and OC-I) transgenic lines (D5-20 and D5-21) of hybrid poplar (Populus × euramericana 'Guariento') using both gas chromatography-mass spectrometry (GC-MS) and ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). We aimed to explore the effects of the exogenous genes on metabolite composition and to screen out metabolites with important biological functions. Finally, we identified 239 named metabolites and determined their relative abundance. Among these, 197 metabolites had a different abundance across the three lines. These methabolites spanned nine primary and 44 secondary metabolism pathways. Arginine and glutamate, as substrates and intermediates in nitrogen metabolism, and important in growth and stress-related processes, as well as sucrose, uridine diphosphate glucose, and their derivatives, precursors in cell wall pathways, and catechol, relevant to insect resistance, differed greatly between the genetically modified and non-transgenic poplar. These findings may provide a basis for further study of cambium metabolism, and fully understand metabolites associated with stress response.

A Combined LC-MS Metabolomics- and 16S rRNA Sequencing Platform to Assess Interactions between Herbal Medicinal Products and Human Gut Bacteria in Vitro: a Pilot Study on Willow Bark Extract

Herbal preparations are complex mixtures of natural products, many of which are able to reach the distal gut due to low oral bioavailability. There, they can influence the microbial communities, and can be metabolized into potentially absorbable bioactive compounds by the intestinal bacteria. This aspect has often been disregarded when searching for the active principles of medicinal plants and herbal medicinal products. The aim of this study was to establish an interdisciplinary platform to unravel interactions of herbal medicine and intestinal microbiota, using a combined LC-MS metabolomics and 16S rRNA microbiome sequencing approach. Willow bark extract (WBE), a herbal medicinal product with a long history of traditional use and a well-established anti-inflammatory activity, was incubated with human fecal suspension under anoxic conditions. Samples were taken after 0.5, 4, and 24 h of incubation. Microbiome analyses revealed that incubation with WBE had a marked effect on microbial community composition and functions. For example, the proportion of Bacteroides sp. was clearly enhanced when the fecal sample used in this study was incubated with WBE. LC-MS analysis showed that WBE constituents were readily metabolized by fecal bacteria. Numerous microbial metabolites could be annotated, allowing the construction of putative microbial degradation pathways for the main groups of WBE constituents. We suggest that studies of this type help to increase the knowledge on bioactive principles of medicinal plants, since gut microbial metabolites might have been underestimated as a source of bioactive compounds in the past.

NAC Transcription Factors in Senescence: From Molecular Structure to Function in Crops

Within the last decade, NAC transcription factors have been shown to play essential roles in senescence, which is the focus of this review. Transcriptome analyses associate approximately one third of Arabidopsis NAC genes and many crop NAC genes with senescence, thereby implicating NAC genes as important regulators of the senescence process. The consensus DNA binding site of the NAC domain is used to predict NAC target genes, and protein interaction sites can be predicted for the intrinsically disordered transcription regulatory domains of NAC proteins. The molecular characteristics of these domains determine the interactions in gene regulatory networks. Emerging local NAC-centered gene regulatory networks reveal complex molecular mechanisms of stress- and hormone-regulated senescence and basic physiological steps of the senescence process. For example, through molecular interactions involving the hormone abscisic acid, Arabidopsis NAP promotes chlorophyll degradation, a hallmark of senescence. Furthermore, studies of the functional rice ortholog, OsNAP, suggest that NAC genes can be targeted to obtain specific changes in lifespan control and nutrient remobilization in crop plants. This is also exemplified by the wheat NAM1 genes which promote senescence and increase grain zinc, iron, and protein content. Thus, NAC genes are promising targets for fine-tuning senescence for increased yield and quality.