Uncovering mechanisms of rubber biosynthesis in Taraxacum koksaghyz - role of cis-prenyltransferase-like 1 protein

Selection and validation of reference genes for quantitative real-time PCR analysis across tissues at different developmental stages in Taraxacum kok-saghyz

Quantitative real-time polymerase chain reaction (qRT-PCR) is a highly sensitive and widely used method for analyzing gene expression profiles. Accurate qRT-PCR normalization requires the identification of stable reference genes under specific experimental conditions. Although seven reference genes have been used in Taraxacum kok-saghyz (TKS), an alternative natural rubber-producing crop, a systematic identification of reliable internal references for gene expression analysis across tissues at distinct developmental stages of TKS has not been conducted. In this study, we screened 12 candidate reference genes (CRGs) based on RNA-seq data from 26 TKS samples, representing five tissue types and nine developmental stages. The expression levels of the 12 CRGs, along with 7 previously reported reference genes (RRGs), were quantified by qRT-PCR across various tissues and developmental stages. The expression stability of the 19 genes was further evaluated by four commonly used algorithms (geNorm, NormFinder, comparative delta Ct, and BestKeeper), and their results were integrated by RefFinder to generate a comprehensive stability ranking. The final results revealed that TkADF1 and TkRPT6A were the most suitable internal control genes for the all-tissue group and leaf samples. TkUPL and TkSIZ1 were found to be optimal for root samples, while TkADF1 and TkSRPRA were preferred choices for latex samples. Moreover, validation using two rubber biosynthesis-related genes (TkFPS1 and TkSRPP2) confirmed the reliability of these recommended genes, showing a strong positive correlation with the RNA-seq data. This study provides reliable reference genes for qRT-PCR normalization in TKS, facilitating future research on developmental regulation and natural rubber biosynthesis.

The cis-prenyltransferase protein family in Taraxacum koksaghyz

The cis-prenyltransferase (cisPT) enzyme family is involved in diverse biological processes that require the synthesis of linear isoprenoid compounds. Taraxacum koksaghyz is a rubber-producing species and potential crop that has eight cisPT homologs (TkCPT1-8) but their distribution and functions are unclear. We compared the structural organization and sequence homology of the proteins, and defined two groups: TkCPT and TkCPT-like (TkCPTL) proteins that form heteromeric cisPT enzymes (TkCPT1-4), and TkCPT proteins that function as homomeric cisPTs (TkCPT5-8). We found that TkCPT1 and TkCPT2 are predominantly expressed in latex whereas TkCPT3 and TkCPT6-8 are predominantly expressed in leaves. TkCPT4 was constitutively expressed in all T. koksaghyz tissues and TkCPT5 mRNA was detected in flowers. The TkCPT1-4 subunits localized to the endoplasmic reticulum whereas TkCPT5-7 were located in chloroplasts. TkCPT1-4 interacted with TkCPTL1-2, forming heteromeric complexes that complemented yeast lacking cisPT. Homomeric TkCPT6 could also complement yeast lacking cisPT but we observed no cisPT activity for TkCPT5, TkCPT7, or TkCPT8 in yeast functional complementation assays. TkCPT1/TkCPTL1 and TkCPT2/TkCPTL1 expressed in yeast produced extra-long-chain polyisoprenes, whereas TkCPT3/TkCPTL1 and TkCPT4/TkCPTL1 produced long-chain dolichols and polyisoprenes, TkCPT5 and TkCPT6 produced medium-chain polyisoprenes, and TkCPT7 and TkCPT8 catalyzed the formation of nerol. The complexity of cisPT proteins in T. koksaghyz suggests that they synthesize different metabolites in a tissue-specific manner, and thus play distinct roles in isoprenoid metabolism. This is the first comprehensive analysis of the localization, interactions, and products of the entire T. koksaghyz cisPT family in vivo, also revealing a novel pentaprenol found specifically in flowers.

Genome-Wide Analysis of the Cis-Prenyltransferase (CPT) Gene Family in Taraxacum kok-saghyz Provides Insights into Its Expression Patterns in Response to Hormonal Treatments

Taraxacum kok-saghyz (TKS) is a natural rubber (NR)-producing plant with great development prospects. Accurately understanding the molecular mechanism of natural rubber biosynthesis is of great significance. Cis-prenyltransferase (CPT) and cis-prenyltransferase-like (CPTL) proteins catalyze the elongation of natural rubber molecular chains and play an essential role in rubber biosynthesis. In this study, we performed a genome-wide identification of the TkCPT/CPTL family, with eight CPT and two CPTL members. We analyzed the gene structures, evolutionary relationships and expression patterns, revealing five highly conserved structural domains. Based on systematic evolutionary analysis, CPT/CPTL can be divided into six subclades, among which the family members are most closely related to the orthologous species Taraxacum mongolicum. Collinearity analyses showed that fragment duplications were the primary factor of amplification in the TkCPT/CPTL gene family. Induced by ethylene and methyl jasmonate hormones, the expression levels of most genes increased, with significant increases in the expression levels of TkCPT5 and TkCPT6. Our results provide a theoretical basis for elucidating the role of the TkCPT/CPTL gene family in the mechanism of natural rubber synthesis and lay a foundation for molecular breeding of T. kok-saghyz and candidate genes for regulating natural rubber biosynthesis in the future.

The interaction networks of small rubber particle proteins in the latex of Taraxacum koksaghyz reveal diverse functions in stress responses and secondary metabolism

The Russian dandelion (Taraxacum koksaghyz) is a promising source of natural rubber (NR). The synthesis of NR takes place on the surface of organelles known as rubber particles, which are found in latex - the cytoplasm of specialized cells known as laticifers. As well as the enzymes directly responsible for NR synthesis, the rubber particles also contain small rubber particle proteins (SRPPs), the most abundant of which are SRPP3, 4 and 5. These three proteins support NR synthesis by maintaining rubber particle stability. We used homology-based searches to identify the whole TkSRPP gene family and qPCR to create their spatial expression profiles. Affinity enrichment-mass spectrometry was applied to identify TkSRPP3/4/5 protein interaction partners in T. koksaghyz latex and selected interaction partners were analyzed using qPCR, confocal laser scanning microscopy and heterologous expression in yeast. We identified 17 SRPP-like sequences in the T. koksaghyz genome, including three apparent pseudogenes, 10 paralogs arranged as an inverted repeat in a cluster with TkSRPP3/4/5, and one separate gene (TkSRPP6). Their sequence diversity and different expression profiles indicated distinct functions and the latex interactomes obtained for TkSRPP3/4/5 suggested that TkSRPP4 is a promiscuous hub protein that binds many partners from different compartments, whereas TkSRPP3 and 5 have more focused interactomes. Two interactors shared by TkSRPP3/4/5 (TkSRPP6 and TkUGT80B1) were chosen for independent validation and detailed characterization. TkUGT80B1 triterpenoid glycosylating activity provided first evidence for triterpenoid saponin synthesis in T. koksaghyz latex. Based on its identified interaction partners, TkSRPP4 appears to play a special role in the endoplasmic reticulum, interacting with lipidmodifying enzymes that may facilitate rubber particle formation. TkSRPP5 appears to be involved in GTPase-dependent signaling and TkSRPP3 may act as part of a kinase signaling cascade, with roles in stress tolerance. TkSRPP interaction with TkUGT80B1 draws a new connection between TkSRPPs and triterpenoid saponin synthesis in T. koksaghyz latex. Our data contribute to the functional differentiation between TkSRPP paralogs and demonstrate unexpected interactions that will help to further elucidate the network of proteins linking TkSRPPs, stress responses and NR biosynthesis within the cellular complexity of latex.

Genome-Wide Identification of the Geranylgeranyl Pyrophosphate Synthase (GGPS) Gene Family Associated with Natural Rubber Synthesis in Taraxacum kok-saghyz L. Rodin

Taraxacum kok-saghyz Rodin (TKS) is a recognized alternative source of natural rubber comparable to the rubber tree. The geranylgeranyl pyrophosphate synthase (GGPS) catalyzed the synthesis of geranylgeranyl pyrophosphate (GGPP), which is an important enzyme in the secondary metabolism pathway. In this study, we present the first analysis of the GGPS gene family in TKS, where a total of seven TkGGPS family members were identified. Their core motifs, conserved structural domains, gene structures, and cis-acting elements were described. In addition, two phylogenetic trees were constructed based on the Neighbor-Joining and Maximum-Likelihood methods, and the TkGGPSs were highly conserved and exhibited good collinearity with the other species. Transcriptome data showed that seven TkGGPS gene members were expressed in all the 12 tissues measured, and TkGGPS1, TkGGPS3, and TkGGPS6 were highly expressed in latex, suggesting that they may be associated with natural rubber synthesis. Meanwhile, quantitative real-time PCR (qRT-PCR) showed that the expression levels of the TkGGPS genes were regulated by the ethylene and methyl jasmonate (MeJA) pathways. Subcellular localization results indicated that all the TkGGPS proteins were also located in chloroplasts involved in photosynthesis in plants. This study will provide valuable insights into the selection of candidate genes for molecular breeding and natural rubber biosynthesis in TKS.

Epigenetic variation in early and late flowering plants of the rubber-producing Russian dandelion Taraxacum koksaghyz provides insights into the regulation of flowering time

The Russian dandelion (Taraxacum koksaghyz) grows in temperate zones and produces large amounts of poly(cis-1,4-isoprene) in its roots, making it an attractive alternative source of natural rubber. Most T. koksaghyz plants require vernalization to trigger flower development, whereas early flowering varieties that have lost their vernalization dependence are more suitable for breeding and domestication. To provide insight into the regulation of flowering time in T. koksaghyz, we induced epigenetic variation by in vitro cultivation and applied epigenomic and transcriptomic analysis to the resulting early flowering plants and late flowering controls, allowing us to identify differences in methylation patterns and gene expression that correlated with flowering. This led to the identification of candidate genes homologous to vernalization and photoperiodism response genes in other plants, as well as epigenetic modifications that may contribute to the control of flower development. Some of the candidate genes were homologous to known floral regulators, including those that directly or indirectly regulate the major flowering control gene FT. Our atlas of genes can be used as a starting point to investigate mechanisms that control flowering time in T. koksaghyz in greater detail and to develop new breeding varieties that are more suited to domestication.

Characterization of natural rubber concerning its components and molecular weight in Taraxacum kok-saghyz Rodin using pyrolysis gas chromatography-mass spectrometry

Taraxacum kok-saghyz Rodin (TKS) has abundant natural rubber in its root and the molecular weight of its natural rubber is higher than that in Hevea brasiliensis. Thus, TKS is an excellent alternative for the commercial production of natural rubber. The content and molecular weight of natural rubber are two qualitative indicators. Efficient determination for both indicators is still a challenge. In this study, we developed a method to simultaneously determine the content and molecular weight of natural rubber in TKS with pyrolysis－gas chromatography-mass spectrometry. The content of natural rubber was quantified by internal standard method. We optimized the pyrolysis temperature and chromatographic method during content determination. The limits of detection and quantification were 0.47 and 1.56 μg, respectively. In addition, the arachidonic acid methyl ester, an unsaturated fatty acid proposed from the α-end group of natural rubber, was quantified to obtain the number of natural rubber polymers. Based on the content and the polymer number, we also quantified the molecular weight of natural rubber. Thus, the content and molecular weight of natural rubber were simultaneously determined in TKS. Our study provides a new perspective for the high throughput analysis of natural rubber.

Overexpression of a pseudo-etiolated-in-light-like protein in Taraxacum koksaghyz leads to a pale green phenotype and enables transcriptome-based network analysis of photomorphogenesis and isoprenoid biosynthesis

Introduction

Plant growth and greening in response to light require the synthesis of photosynthetic pigments such as chlorophylls and carotenoids, which are derived from isoprenoid precursors. In Arabidopsis, the pseudo-etiolated-in-light phenotype is caused by the overexpression of repressor of photosynthetic genes 2 (RPGE2), which regulates chlorophyll synthesis and photosynthetic genes.

Methods

We investigated a homologous protein in the Russian dandelion (Taraxacum koksaghyz) to determine its influence on the rich isoprenoid network in this species, using a combination of in silico analysis, gene overexpression, transcriptomics and metabolic profiling.

Results

Homology-based screening revealed a gene designated pseudo-etiolated-in-light-like (TkPEL-like), and in silico analysis identified a light-responsive G-box element in its promoter. TkPEL-like overexpression in dandelion plants and other systems reduced the levels of chlorophylls and carotenoids, but this was ameliorated by the mutation of one or both conserved cysteine residues. Comparative transcriptomics in dandelions overexpressing TkPEL-like showed that genes responsible for the synthesis of isoprenoid precursors and chlorophyll were downregulated, probably explaining the observed pale green leaf phenotype. In contrast, genes responsible for carotenoid synthesis were upregulated, possibly in response to feedback signaling. The evaluation of additional differentially expressed genes revealed interactions between pathways.

Discussion

We propose that TkPEL-like negatively regulates chlorophyll- and photosynthesis-related genes in a light-dependent manner, which appears to be conserved across species. Our data will inform future studies addressing the regulation of leaf isoprenoid biosynthesis and photomorphogenesis and could be used in future breeding strategies to optimize selected plant isoprenoid profiles and generate suitable plant-based production platforms.

Molecular Genetic Research and Genetic Engineering of Taraxacum kok-saghyz L.E. Rodin

Natural rubber (NR) remains an indispensable raw material with unique properties that is used in the manufacture of a large number of products and the global demand for it is growing every year. The only industrially important source of NR is the tropical tree Hevea brasiliensis (Willd. ex A.Juss.) Müll.Arg., thus alternative sources of rubber are required. For the temperate zone, the most suitable source of high quality rubber is the Russian (Kazakh) dandelion Taraxacum kok-saghyz L.E. Rodin (TKS). An obstacle to the widespread industrial cultivation of TKS is its high heterozygosity, poor growth energy, and low competitiveness in the field, as well as inbreeding depression. Rapid cultivation of TKS requires the use of modern technologies of marker-assisted and genomic selection, as well as approaches of genetic engineering and genome editing. This review is devoted to describing the progress in the field of molecular genetics, genomics, and genetic engineering of TKS. Sequencing and annotation of the entire TKS genome made it possible to identify a large number of SNPs, which were subsequently used in genotyping. To date, a total of 90 functional genes have been identified that control the rubber synthesis pathway in TKS. The most important of these proteins are part of the rubber transferase complex and are encoded by eight genes for cis-prenyltransferases (TkCPT), two genes for cis-prenyltransferase-like proteins (TkCPTL), one gene for rubber elongation factor (TkREF), and nine genes for small rubber particle proteins (TkSRPP). In TKS, genes for enzymes of inulin metabolism have also been identified and genome-wide studies of other gene families are also underway. Comparative transcriptomic and proteomic studies of TKS lines with different accumulations of NR are also being carried out, which help to identify genes and proteins involved in the synthesis, regulation, and accumulation of this natural polymer. A number of authors already use the knowledge gained in the genetic engineering of TKS and the main goal of these works is the rapid transformation of the TKS into an economically viable rubber crop. There are no great successes in this area so far, therefore work on genetic transformation and genome editing of TKS should be continued, considering the recent results of genome-wide studies.

Differential gene expression in chronically irradiated herbaceous species from the Chernobyl exclusion zone

PURPOSE

Transcriptional activity of genes related to ionizing radiation responses in chronically irradiated plant populations at radioactively contaminated territories can be a cost-effective and precise approach for stress response evaluation. However, there are limits to studying non-model plants in field conditions. The work studies the transcriptional activity of candidate genes of adaptation to chronic radiation exposure in plant populations from radioactively contaminated territories of the Chernobyl.

MATERIALS AND METHODS

In this work, we studied plant species with different sensitivity to acute irradiation: Trifolium repens L., Taraxacum officinale Wigg., and Dactylis glomerata L., sampled in the Chernobyl exclusion zone. The differential expression of several candidate genes of adaptation to chronic radiation exposure in the leaves of these species was analyzed, including homologs of Arabidopsis thaliana genes SLAC1, APX1, GPX2, CAB1, NTRB, PP2-B11, RBOH-F, HY5, SnRK2.4, PDS1, CIPK20, SIP1, PIP1, TIP1.

RESULTS AND CONCLUSIONS

All studied species were characterized by upregulation of the CAB1 homolog, encoding chlorophyll a/b binding protein, at radioactively contaminated plots. An increase in the expression of genes associated with water and hydrogen peroxide transport, intensity of photosynthesis, and stress responses (homolog of aquaporin TIP1 for T. repens; homologs of aquaporin PIP1 and transcription factor HY5 for D. glomerata; homolog of CBL-interacting serine/threonine protein kinase CIPK20 for T. officinale) was revealed. The methodological approach for studying gene expression in non-model plant species is described, which may allow large-scale screening studies of candidate genes in various plant species abundant in radioactively contaminated areas.

Downregulation of HbFPS1 affects rubber biosynthesis of Hevea brasiliensis suffering from tapping panel dryness

Tapping panel dryness (TPD) is a century-old problem that has plagued the natural rubber production of Hevea brasiliensis. TPD may result from self-protective mechanisms of H. brasiliensis in response to stresses such as excessive hormone stimulation and mechanical wounding (bark tapping). It has been hypothesized that TPD impairs rubber biosynthesis; however, the underlying mechanisms remain poorly understood. In the present study, we firstly verified that TPD-affected rubber trees exhibited lower rubber biosynthesis activity and greater rubber molecular weight compared to healthy rubber trees. We then demonstrated that HbFPS1, a key gene of rubber biosynthesis, and its expression products were downregulated in the latex of TPD-affected rubber trees, as revealed by transcriptome sequencing and iTRAQ-based proteome analysis. We further discovered that the farnesyl diphosphate synthase HbFPS1 could be recruited to small rubber particles by HbSRPP1 through protein-protein interactions to catalyze farnesyl diphosphate (FPP) synthesis and facilitate rubber biosynthesis initiation. FPP content in the latex of TPD-affected rubber trees was significantly decreased with the downregulation of HbFPS1, ultimately resulting in abnormal development of rubber particles, decreased rubber biosynthesis activity, and increased rubber molecular weight. Upstream regulator assays indicated that a novel regulator, MYB2-like, may be an important regulator of downregulation of HbFPS1 in the latex of TPD-affected rubber trees. Our findings not only provide new directions for studying the molecular events involved in rubber biosynthesis and TPD syndrome and contribute to rubber management strategies, but also broaden our knowledge of plant isoprenoid metabolism and its regulatory networks.

Construction of the first high-density SNP genetic map and identification of QTLs for the natural rubber content in Taraxacum kok-saghyz Rodin

BACKGROUND

Taraxacum kok-saghyz Rodin (TKS) is a promising commercial alternative natural rubber (NR) yielding plant. Cultivating TKS with a high NR content is an important breeding target, and developing molecular markers related to NR content can effectively accelerate the breeding process of TKS.

RESULTS

To construct a high-density SNP genetic map and uncover genomic regions related to the NR content in TKS, an F₁ mapping population of TKS was constructed by crossing two parents (l66 and X51) with significant differences in NR contents. The NR content of the F₁ plants ranged from 0.30 to 15.14% and was distributed normally with a coefficient of variation of 47.61%, indicating quantitative trait inheritance. Then, employing whole-genome resequencing (WGR), a TKS genetic linkage map of 12,680 bin markers comprising 322,439 SNPs was generated. Based on the genetic map and NR content of the F₁ population, six quantitative trait loci (QTLs) for NR content with LOD > 4.0 were identified on LG01/Chr01 and LG06/Chr06. Of them, the 2.17 Mb genomic region between qHRC-C6-1 and qHRC-C6-2 on ChrA06, with 65.62% PVE in total, was the major QTL region. In addition, the six QTLs have significant additive genetic effects on NR content and could be used to develop markers for marker-assisted selection (MAS) in TKS with a high NR content.

CONCLUSION

This work constructed the first high-density TKS genetic map and identified the QTLs and genomic regions controlling the NR content, which provides useful information for fine mapping, map-based cloning, and MAS in TKS.

Natural rubber reduces herbivory and alters the microbiome below ground

Laticifers are hypothesized to mediate both plant-herbivore and plant-microbe interactions. However, there is little evidence for this dual function. We investigated whether the major constituent of natural rubber, cis-1,4-polyisoprene, a phylogenetically widespread and economically important latex polymer, alters plant resistance and the root microbiome of the Russian dandelion (Taraxacum koksaghyz) under attack of a root herbivore, the larva of the May cockchafer (Melolontha melolontha). Rubber-depleted transgenic plants lost more shoot and root biomass upon herbivory than normal rubber content near-isogenic lines. Melolontha melolontha preferred to feed on artificial diet supplemented with rubber-depleted rather than normal rubber content latex. Likewise, adding purified cis-1,4-polyisoprene in ecologically relevant concentrations to diet deterred larval feeding and reduced larval weight gain. Metagenomics and metabarcoding revealed that abolishing biosynthesis of natural rubber alters the structure but not the diversity of the rhizosphere and root microbiota (ecto- and endophytes) and that these changes depended on M. melolontha damage. However, the assumption that rubber reduces microbial colonization or pathogen load is contradicted by four lines of evidence. Taken together, our data demonstrate that natural rubber biosynthesis reduces herbivory and alters the plant microbiota, which highlights the role of plant-specialized metabolites and secretory structures in shaping multitrophic interactions.

Another level of complex-ity: The role of metabolic channeling and metabolons in plant terpenoid metabolism

Terpenoids constitute one of the largest and most diverse classes of plant metabolites. While some terpenoids are involved in essential plant processes such as photosynthesis, respiration, growth, and development, others are specialized metabolites playing roles in the interaction of plants with their biotic and abiotic environment. Due to the distinct functions and properties of specific terpenoid compounds, there is a growing interest to introduce or modify their production in plants by metabolic engineering for agricultural, pharmaceutical, or industrial applications. The MVA and MEP pathways and the prenyltransferases providing the general precursors for terpenoid formation, as well as the enzymes of the various downstream metabolic pathways leading to the formation of different groups of terpenoid compounds have been characterized in detail in plants. In contrast, the molecular mechanisms directing the metabolic flux of precursors specifically toward one of several potentially competing terpenoid biosynthetic pathways are still not well understood. The formation of metabolons, multi-protein complexes composed of enzymes catalyzing sequential reactions of a metabolic pathway, provides a promising concept to explain the metabolic channeling that appears to occur in the complex terpenoid biosynthetic network of plants. Here we provide an overview about examples of potential metabolons involved in plant terpenoid metabolism that have been recently characterized and the first attempts to utilize metabolic channeling in terpenoid metabolic engineering. In addition, we discuss the gaps in our current knowledge and in consequence the need for future basic and applied research.

Reconstitution of prenyltransferase activity on nanodiscs by components of the rubber synthesis machinery of the Para rubber tree and guayule

Natural rubber of the Para rubber tree (Hevea brasiliensis) is synthesized as a result of prenyltransferase activity. The proteins HRT1, HRT2, and HRBP have been identified as candidate components of the rubber biosynthetic machinery. To clarify the contribution of these proteins to prenyltransferase activity, we established a cell-free translation system for nanodisc-based protein reconstitution and measured the enzyme activity of the protein-nanodisc complexes. Co-expression of HRT1 and HRBP in the presence of nanodiscs yielded marked polyisoprene synthesis activity. By contrast, neither HRT1, HRT2, or HRBP alone nor a complex of HRT2 and HRBP manifested such activity. Similar analysis of guayule (Parthenium argentatum) proteins revealed that three HRT1 homologs (PaCPT1-3) manifested prenyltransferase activity only when co-expressed with PaCBP, the homolog of HRBP. Our results thus indicate that two heterologous subunits form the core prenyltransferase of the rubber biosynthetic machinery. A recently developed structure modeling program predicted the structure of such heterodimer complexes including HRT1/HRBP and PaCPT2/PaCBP. HRT and PaCPT proteins were also found to possess affinity for a lipid membrane in the absence of HRBP or PaCBP, and structure modeling implicated an amphipathic α-helical domain of HRT1 and PaCPT2 in membrane binding of these proteins.

Comparative Transcriptome Analysis in Taraxacum koksaghyz to Identify Genes that Determine Root Volume and Root Length

The Russian dandelion (Taraxacum koksaghyz, family Asteraceae) produces large amounts of natural rubber in the laticifers of its roots. This species has been proposed as an alternative source of natural rubber to augment or partly replace the rubber tree (Hevea brasiliensis) but domestication would require genetic improvement to increase rubber yields and agronomic optimization to facilitate harvesting and processing. Optimization has focused thus far on the size and shape of the roots, the primary storage organ for natural rubber and inulin. However, the corresponding genetic factors are poorly understood. Here we describe the comparative transcriptomic analysis of root tissues from T. koksaghyz plant sets featuring different root sizes and shapes, aiming to identify differentially expressed genes correlating with root length or root diameter in the upper root and root tip. The resulting datasets revealed multiple candidate genes for each trait and root part, including a glucan endo-1,3-β-d-glucosidase, an allene oxide synthase 3, and a TIFY10A/JAZ1 homolog. These three genes were tested by qRT-PCR in outdoor-grown plants with diverse root morphology, and the expression of two genes correlated with the appropriate root morphotype, confirming the effectiveness of our method. We evaluated the candidate genes to gain insight into their potential functions in root development. Such candidate genes could be suitable for marker-assisted breeding programs in the future.

Sustainable mobility: The route of tires through the circular economy model

Until nowadays, the concept of the 3Rs (Reduce, Reuse, Recycle) has tried to develop responsible consumption habits. Nonetheless, the rise of ecological thinking has generated the appearance of four new Rs in addition to these basic 3Rs; the currently 7Rs (Reduce, Reuse, Recycle, Redesign, Renew, Repair and Recover) which refer to the actions necessary to achieve the change towards a circular economy (CE) model. This model aims at extending the lifetime of the resources through their rational and efficient use to generate value repeatedly, reducing costs and waste. In this review, we examine the route followed by tires from the CE perspective, analyzing end-of-life strategies that aim to improve the circular flow of tire rubber materials. We discuss the most relevant studies on the "7Rs" concepts applied to tires, comparing different scientific approaches, as well as their industrial and commercial implementation. We also illustrate the drawbacks and feasibility of each of the R-hierarchy strategies. From the early stages of production to the post-consumption step, the path that tires trail within this CE model evidences the commitment and efforts towards the development of effective management schemes for achieving a real sustainable mobility.

Latex Metabolome of Euphorbia Species: Geographical and Inter-Species Variation and its Proposed Role in Plant Defense against Herbivores and Pathogens

Based on the hypothesis that the variation of the metabolomes of latex is a response to selective pressure and should thus be affected differently from other organs, their variation could provide an insight into the defensive chemical selection of plants. Metabolic profiling was used to compare tissues of three Euphorbia species collected in diverse regions. The metabolic variation of latexes was much more limited than that of other organs. In all the species, the levels of polyisoprenes and terpenes were found to be much higher in latexes than in leaves and roots of the corresponding plants. Polyisoprenes were observed to physically delay the contact of pathogens with plant tissues and their growth. A secondary barrier composed of terpenes in latex and in particular, 24-methylenecycloartanol, exhibited antifungal activity. These results added to the well-known role of enzymes also present in latexes, show that these are part of a cooperative defense system comprising biochemical and physical elements.

Microscopic and Transcriptomic Analysis of Pollination Processes in Self-Incompatible Taraxacum koksaghyz

The transition of the Russian dandelion Taraxacum koksaghyz (Asteraceae) to a profitable, alternative crop producing natural rubber and inulin requires the optimization of several agronomic traits, cultivation conditions and harvesting procedures to improve the yield. However, efficient breeding is hindered by the obligatory sexual outcrossing of this species. Several other asters have been investigated to determine the mechanism of self-incompatibility, but the underlying molecular basis remains unclear. We therefore investigated the self-pollination and cross-pollination of two compatible T. koksaghyz varieties (TkMS2 and TkMS3) by microscopy and transcriptomic analysis to shed light on the pollination process. Self-pollination showed typical sporophytic self-incompatibility characteristics, with the rare pollen swelling at the pollen tube apex. In contrast, cross-pollination was characterized by pollen germination and penetration of the stigma by the growing pollen tubes. RNA-Seq was used to profile gene expression in the floret tissue during self-pollination and cross-pollination, and the differentially expressed genes were identified. This revealed three candidates for the early regulation of pollination in T. koksaghyz, which can be used to examine self-incompatibility mechanisms in more detail and to facilitate breeding programs.