Hevea Research Articles

Rubber seed shell as low-cost medium to produce lactic acid using Lactobacillus plantarum LB2 and fabrication of a polylactic acid-chitosan composite for fish fillet packing

Rubber seed shell (Hevea brasiliensis) was used as a low-cost substrate to produce lactic acid via Lactobacillus plantarum LB2. The medium components were initially screened by two-level full factorial design. Three variables (pH, moisture, and polyoxyethylene sorbitan monooleate (PSM)) were used in the central composite design and response surface methodology. The amount of PSM was found to be a significant variable in lactic acid production. Lactic acid was purified and used for the chemical fabrication of a polylactic acid-chitosan composite film. Compared with the polylactic acid, the composite film improved the tensile strength, elongation strength, and tearing strength. The film prepared with 1% chitosan-polylactic acid exhibited the maximum antibacterial activity against Bacillus cereus (21 ± 1 mm) and the lowest activity against Escherichia coli (10 ± 1 mm). The polylactic acid-chitosan film prepared with 1% chitosan was used as a packing material to store the fish fillets and presented reduced mesophilic (4.3 ± 0.1 Log CFU/g) and psychrotropic (3.2 ± 0.2 Log CFU/g) bacterial populations compared with those of the control (4.9 ± 0.2 Log CFU/g and 3.7 Log CFU/g). Rubber seed shells can be used as an alternative culture medium for lactic acid production, to reduce the production cost of polylactic acid.

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.

Resilience underground: Understanding earthworm biomass responses to land use changes in the tropics

Soil biodiversity, like terrestrial biodiversity, is currently under threat by changes in land use. Intensively managed farming activities with agrochemicals have degraded both soil biodiversity and health. However, little is known about how these changes in land use affect the distribution of earthworm biomass in Southeast Asia. We conducted earthworm sampling across multiple habitats, including lowland forests, exotic monoculture plantations (e.g., oil palm and rubber tree), and agroforestry orchards. To survey earthworm populations, we excavated the top 30 cm of soil at 18 sites encompassing 399 plots distributed across natural and human-modified ecosystems in Selangor and Negeri Sembilan, Peninsular Malaysia. We found that earthworm abundance was negatively related to increasing soil compaction, leaf litter weight, soil pH, and undergrowth height, whereas it was positively associated with increasing undergrowth and canopy cover. Our findings demonstrated that agroforestry orchards, rubber tree plantations, and mature oil palm plantations had higher earthworm abundance than those in logged lowland forests. Earthworm abundance in unlogged lowland forests and young oil palm plantations, on the other hand, was lower than in logged lowland forests. Overall earthworm weight was greater in rubber tree plantations, agroforestry orchards, mature oil palm plantations, and unlogged lowland forests than those in logged lowland forests, while young oil palm plantations exhibited lower earthworm weight than logged lowland forests. Our data indicate that increases in soil compaction and leaf litter weight were associated with decreased earthworm weight. These results demonstrate the importance of site-level habitat management for maintaining healthy earthworm populations and soil biodiversity.

Enhancing bioenergy and feed production in Southern Thailand: An approach through Leucaena cultivation and hydrothermal carbonization

This study addresses sustainability challenges in Southern Thailand, particularly the scarcity of biomass fuel and animal feed. It investigates the integration of Leucaena leucocephala cultivation with hydrothermal carbonization. The research compares the biomass yield and economic feasibility of growing Leucaena as a sole crop versus intercropping it with Para rubber trees. Sole cropping Leucaena produces higher biomass yields and is more economically viable. The wood stem of Leucaena is competitive with other biomass fuels used in local power plants, while its leaves, with over 14 % protein content, meet local animal feed market standards. Additionally, branches, which constitute 15.15 % to 30.58 % of the total biomass, are usually left as residue but can be used for hydrochar production. The study examines the effects of temperature (235 °C and 265 °C) and retention time (1, 2, and 3 hours) on hydrochar properties. Optimal condition (265 °C for 1 hour) produces hydrochar with high heating value and energy yield. Using these branches for hydrochar can significantly boost total revenue, with hydrochar contributing 54.9 % to overall revenue (4522.00 USD/ha). Integrating Leucaena cultivation with hydrothermal carbonization offers a sustainable solution, enhancing revenue, supporting local energy and feed needs, and promoting environmental sustainability.

Cellulose nanofibers-based UV resistant and hydrophobic wood coatings

Wood and wood-based products are regarded as sustainable building materials, nonetheless, they frequently need the addition of protective coatings due to their susceptibility to abiotic and biotic degrading elements. Among the coating systems, water-borne coatings are a better choice since the majority of popular wood coatings are solvent-based and release volatile organic chemicals (VOCs). In this study, cellulose nanofibers (CNFs) were isolated from eucalyptus wood pulp using a chemo-mechanical method and used as the base substrate for wood coatings. The effect of CNF dispersion with varying concentrations (0.5 and 1 wt.%) of zinc oxide (ZnO) nanoparticles on UV-resistance of Pinus radiata and Hevea brasiliensis after 500 hrs of exposure was assessed. Wood surfaces without coating exhibited severe discolouration after 500 hrs of UV exposure. Only CNF-coating results in slight protection of wood surfaces from weathering but significantly increased water wettability of the surface. The incorporation of ZnO nanoparticles significantly reduced the colour change of the wood surfaces. As the concentration of ZnO increased, the colour stability and hydrophobicity of both the wood increased.

The rubber tree that changed the world in 150 years

The rubber tree that changed the world in 150 years

Current status and prospects of research on main diseases of rubber trees

Current status and prospects of research on main diseases of rubber trees

Genome-Wide Identification of Rubber Tree SCAMP Genes and Functional Characterization of HbSCAMP3.

Natural rubber produced by the rubber tree is a vital industrial raw material globally. Seven SCAMP gene family members were identified in the rubber tree, and the phylogenetic tree classified HbSCAMPs into three subfamilies. Significant differences were observed among HbSCAMPs in terms of gene length, number of exons, and composition of conserved motifs. The expansion of HbSCAMPs in the rubber tree genome is associated with segmental duplications. The high expression of HbSCAMP1-6 in petioles and HbSCAMP7 in stem tips, along with their distinct responses to drought, salt, and wound stresses, indicates their crucial roles in substance transport and stress adaptation. Transgenic poplar experiments demonstrated that overexpression of HbSCAMP3 significantly promotes plant height growth, with localization in the tobacco plasma membrane, suggesting its involvement in regulating plant growth through membrane transport processes. These findings enhance the understanding of HbSCAMPs in rubber trees and provide new insights into how plants finely tune gene family members to adapt to environmental changes.

Assessing Drought Impacts on Gross Primary Productivity of Rubber Plantations Using Flux Observations and Remote Sensing in China and Thailand

Rubber (Hevea brasiliensis Muell.) plantations are vital agricultural ecosystems in tropical regions. These plantations provide key industrial raw materials and sequester large amounts of carbon dioxide, playing a vital role in the global carbon cycle. Climate change has intensified droughts in Southeast Asia, negatively affecting rubber plantation growth. Limited in situ observations and short monitoring periods hinder accurate assessment of drought impacts on the gross primary productivity (GPP) of rubber plantations. This study used GPP data from flux observations at four rubber plantation sites in China and Thailand, along with solar-induced chlorophyll fluorescence (SIF), enhanced vegetation index (EVI), normalized difference vegetation index (NDVI), near-infrared reflectance of vegetation (NIRv), and photosynthetically active radiation (PAR) indices, to develop a robust GPP estimation model. The model reconstructed eight-day interval GPP data from 2001 to 2020 for the four sites. Finally, the study analyzed the seasonal drought impacts on GPP in these four regions. The results indicate that the GPP prediction model developed using SIF, EVI, NDVI, NIRv, and PAR has high accuracy and robustness. The model’s predictions have a relative root mean square error (rRMSE) of 0.22 compared to flux-observed GPP, with smaller errors in annual GPP predictions than the MOD17A3HGF model, thereby better reflecting the interannual variability in the GPP of rubber plantations. Drought significantly affects rubber plantation GPP, with impacts varying by region and season. In China and northern Thailand (NR site), short-term (3 months) and long-term (12 months) droughts during cool and warm dry seasons cause GPP declines of 4% to 29%. Other influencing factors may alleviate or offset GPP reductions caused by drought. During the rainy season across all four regions and the cool dry season with adequate rainfall in southern Thailand (SR site), mild droughts have negligible effects on GPP and may even slightly increase GPP values due to enhanced PAR. Overall, the study shows that drought significantly impacts rubber the GPP of rubber plantations, with effects varying by region and season. When assessing drought’s impact on rubber plantation GPP or carbon sequestration, it is essential to consider differences in drought thresholds within the climatic context.

Assembly and maintenance of phyllosphere microbial diversity during rubber tree leaf senescence

Phyllosphere microorganisms execute important ecological functions including supporting host plant growth, enhancing host resistance to abiotic stresses, and promoting plant diversity. How leaf developmental stages affect plant-microbiome interactions and phyllosphere microbial community assembly and diversity is poorly understood. In this study, we utilized amplicon sequencing of 16S rRNA and ITS genes to investigate the composition and diversity of microbial communities across different leaf developmental stages of rubber trees. Our findings reveal that endophytic microbial communities, particularly bacterial communities, are more influenced by leaf senescence than by epiphytic communities. The high abundance of metabolism genes in the endosphere of yellow leaves contributes to the degradation and nutrient relocation processes. Nutrient loss leads to a higher abundance of α-Proteobacteria (r-selected microorganisms) in the yellow leaf endosphere, thereby promoting stochastic community assembly. As leaves age, the proportion of microorganisms entering the inner layer of leaves increases, consequently enhancing the diversity of microorganisms in the inner layer of leaves. These results offer insights into the mechanisms governing community assembly and diversity of leaf bacteria and fungi, thereby advancing our understanding of the evolving functions of microbial communities during leaf senescence in general, and for an important tropical crop species in particular.

Variation in specific gravity and shrinkage of tapped rubberwood

Hevea brasiliensis (rubber tree), a major source of natural rubber, could also be an important source of lumber as senescence occurs. However, latex collection is known to affect Hevea brasiliensis (rubber tree) wood formation and consequently, wood properties. The impact tapping (cutting made in the bark of the tree for latex harvest) has on the tree and the way the tree responds after tapping is often overlooked. Knowledge on wood properties of tapped rubber trees in Nigeria would enhance its sustainable utilization which is especially important in developing countries where lumber is limited. Variation in specific gravity and shrinkage of rubberwood wood due to tapping duration was examined. Tapping duration had significant effect in specific gravity and longitudinal shrinkage of rubberwood but had no effect on tangential and radial shrinkage. The specific gravity (SG) of rubberwood ranged from 0,55 - 0,59. Longitudinal shrinkage (average 1,42 %) was higher than typically observed for mature wood. Average tangential shrinkage for rubberwood of all the ages was 5,37 % while radial shrinkage ranged from 2,87 % to 3,84 %. decrease in SG observed in trees tapped for 20 years may indicate the initiation of senescence. Tapped rubberwood could be used in areas not exposed to high moisture as well as in other wood composites.

In silico analysis of secreted effectorome of the rubber tree pathogen Rigidoporus microporus highlights its potential virulence proteins.

Rigidoporus microporus, the causative agent of the white root rot disease of rubber trees, poses a significant threat to natural rubber production worldwide. Understanding the molecular mechanisms facilitating its pathogenicity would be crucial for developing effective disease management strategies. The pathogen secretes effector proteins, which play pivotal roles in modulating host immune responses and infection. In this study, in silico analyses identified 357 putative secreted effector proteins from the R. microporus genome. These were then integrated into previous RNA-seq data obtained in response to rubber tree latex exposure. Annotation of putative effectors suggested the abundance of proteins in several families associated with the virulence of R. microporus, especially hydrophobin proteins and glycoside hydrolase (GH) proteins. The contribution of secreted effectors to fungal pathogenicity was discussed, particularly in response to rubber tree latex exposure. Some unknown highly expressed effectors were predicted for the protein structures, revealing their similarity to aminopeptidase, ubiquitin ligase, spherulin, and thaumatin protein. This integrative study further elucidates the molecular mechanism of R. microporus pathogenesis and offers alternative targets for developing control strategies for managing white root rot disease in rubber plantations.

Assessment of Agro-morphological Parameters of Two Accessions of Undergrowth Yam (Dioscorea sp.) Cultivated in the Inter-rows of Mature Rubber Trees (Hevea brasiliensis) in Daloa, Côte d’Ivoire

The valorization of mature rubber tree inter-rows by food crops could solve the problem of food insecurity in rubber tree-growing areas. This study aims to assess the agro-morphological parameters of understory yams sown under mature rubber trees. To this end, a trial was carried out in Daloa on a mature rubber tree plantation and a control plot of sole yam. Two accessions of undergrowth yams, “Bacoué” and “Soupkataloa”, were grown in the rubber tree inter-rows and monoculture. The experimental design was a completely randomized block with 15 repetitions. The parameters measured on the yams were emergence rate, specific leaf area (SLA), number of days to emergence, number of days to first leaf, stem height (Ht), crown diameter (CD) and production. The results showed that the accessions tested under rubber trees emerged relatively well, with 66.67% and 70.83% rates for Bacoué and Soupkataloa, respectively. These combined accessions also showed the largest SLAs of 343 cm2/g for Bacoué and 328.5 cm2/g for Soupkataloa during the dry season. However, emergence was late under the rubber trees compared with the yam monoculture. Bacoué emerged 179.19 d after sowing and had its first leaves 42.88 d later, whereas these values were 58.18 d and 11.71 d respectively for Soupkataloa. However, although Bacoué performed better, with an Ht of 825 cm in 70 days and a large CD (11.18 mm), its production was identical to that of Soupkataloa. These results show that undergrowth yams can be combined with mature rubber trees to guarantee food security.

Insights into pathogenicity mechanisms of Phytophthora meadii, the abnormal leaf fall pathogen in rubber tree, through whole genome sequencing and analysis

Hevea brasiliensis (Willd. ex A.Juss.) Müll. Arg., also known as the Para rubber tree is the main commercial source of natural rubber. Phytophthora meadii causing abnormal leaf fall (ALF) disease is the most destructive and recurrent disease of rubber trees in India, leading to significant annual economic losses. To comprehend its pathogenic mechanisms and investigate stratagems for disease control, whole-genome sequencing and analysis of P. meadii were conducted. The P. meadii genome was sequenced using the standard Illumina Novaseq 6000 Platform. The assembled P. meadii genome is approximately 53 Mb in size, consisting of 13,171 contigs with an N50 of 7105 and a BUSCO completeness of 96 %. A total of 14,646 protein-coding genes were predicted, with an average GC content of 49.96 %. P. meadii's genome contains 750 carbohydrate-active enzymes (CAZymes), which is notably higher compared to closely related species. Five genomic regions potentially encoding enzymes for secondary metabolite production and 1877 pathogenic proteins were also identified. Our data confirm the phylogenetic positioning of P. meadii as a distinct species and indicate that it forms a closely related clade with P. citrophthora. Analyzing the P. meadii genome not only aids in understanding its genomic traits but also facilitates the identification of genes related to pathogenesis and will give a better understanding of the Hevea – Phytophthora interaction.

Euphorbiaceae superoxide dismutase, catalase, and glutathione peroxidase as clues to better comprehend high drought tolerance in castor bean

Superoxide dismutase (SOD), Catalase (CAT), and Glutathione peroxidase (GPX) enzymes exert a central role in reactive oxygen species (ROS) scavenger in plants, being an important part of enzymatic antioxidant system. Despite the importance of these enzymes in ROS metabolism and in different signaling pathways related to plant development and stress response, their gene families have not yet been comprehensively characterized in many crop plants. Among different crops, the Euphorbiaceae family has some species highly tolerant to drought stress. However, the gene families that encode the antioxidant enzymes, as well as their role in this drought stress tolerance, remains not characterized. Here, the SOD, CAT, and GPX genes of castor bean (Ricinus communis), cassava (Manihot esculenta), jatropha (Jatropha curcas), rubber tree (Hevea brasiliensis), petty spurge (Euphorbia peplus), and annual mercury (Mercurialis annua) were identified and characterized. The comprehensive phylogenetic and genomic analyses allowed the classification of the genes into different classes and revealed the duplication events that contribute to the expansion of these families within plant genomes. The expression patterns of SOD, CAT, and GPX genes were examined in castor bean, cassava, jatropha, and rubber tree by RNA-seq analysis revealing differential expression during stress. Additionally, the castor bean gene expression was confirmed by RT-qPCR. Among castor bean genes, RcGPX4 appears to be induced in castor bean roots under drought stress, but the heterologous expression in Arabidopsis thaliana does not improve the drought tolerance. Altogether, this data has significantly contributed to characterizing the expression patterns and conducting evolutionary assessment of these genes in Euphorbiaceae. This bridge a gap in understanding the proposed functions of core components within the antioxidant mechanism in an economically significant group of plants, particularly during stress responses

ISOLATION AND ANALYSIS OF NATIVE DNA AND RNA FROM ROOTS OF RUBBER-PRODUCING SPECIES SCORZONERA TAU-SAGHYZ LIPSCH. ET G.G. BOSSE

Scorzonera tau-saghyz Lipsch. et G.G.Bosse, is endemic species, growing in South Kazakhstan and alternative (to Hevea brasilians) source of natural rubber, related to the Asteraceae Family. Natural rubber (NR) is an indispensable raw material for the production of different products for medicine, automotive and aviation industries. The introduction of tau-saghyz into the culture will make it possible to obtain NC not only in Kazakhstan, but also on the territory of the countries of the Northern latitudes. At the growing phases of ontogenesis of tau-saghyz (April-June) latex is actively synthesized in the leaves and transported to the roots. In our experiments it was necessary to conduct molecular genetic studies of the selected forms of tau-saghyz with high rubber concentration. In this regard, it became necessary to isolate and analyze native DNA and RNA from dry roots. Samples with the highest rubber content were used for DNA extraction. The main problem in the isolation of DNA from the dry roots of tau-saghyz is the significant content of natural rubber. In this research the following commercial kits were used: 1) DNeasy Plant Mini Kit (Qiagene); 2) GenElute Plant Genomic DNA Miniprep Kit (Sigma); 3) NucleoSpin® Plant II / Midi / Maxi kit (Macherey-Nagel). Further DNA isolation was carried out in accordance with the kit manufacturer's protocol. Quantitative DNA analysis was performed using both UV spectrophotometry (Nanodrop) and fluorometric analysis (Qubit) method. DNA extracted by the 2 kit (Sigma) was further purified by precipitation with ethanol and demonstrates satisfactory quality. Functional analysis of isolated DNA samples was performed both by restriction analysis and by DNA amplification. It is worth to mention that for reaction primers that are characteristic of gene AACT (ACETOACETYL-COA TRANSFERASE) Cucumis melo were used. This enzyme catalyzes the first reaction of biosynthesis in the mevalonate pathway, which the final product is IDP (isopentenyl diphosphate). The cis-prenyltransferase (CPT) enzyme catalyzes the biosynthesis of rubber by the sequential addition of IDP to the terminal group of the initiating allylic pyrophosphate (APP). As a result of PCR analysis a putative 1200 bp AAST gene for tau-saghyz was identified. In this study two methods of RNA isolation were chosen: 1. A method widely used for plants of the Cucurbitaceae family; 2. A method approved for plants with a high content of polyphenols. The RNA isolation was carried out as described in the relevant protocols with minor modifications (Verwoerd TC, Dekker BMM, Hoekema A (1989) A small-scale procedure for the rapid isolation of plant RNAs. Nucleic Acids Res 17:2362). The final precipitates were dissolved in 50 µl of water pretreated with diethylpyrocarbonate. Quantitative analysis of RNA was carried out using UV spectrophotometry (Nanodrop). Functional analysis of extracted RNA samples was conducted by cDNA synthesis with usage of reverse transcriptase Superscript IV with the following amplification in PCR. In this reaction the primers specific for CPT gene of Taraxacum kok-saghyz were used. The prospective CPT gene was excised from the gel, purified and cloned into the pJET vector. In the further research it is planned to perform its sequencing and comparison with the CPT gene of Taraxacum kok-saghyz and Hevea brasiliensis.

How Cropping System Influences Robusta Coffee Leaf Gas Exchange Efficiency via Stomatal Regulation

Background: Robusta coffee leaves regulate gas exchange in response to climatic factors like full sun and shaded conditions. To fully understand the reasons behind the variations in photosynthetic rates and water-use efficiency, exploring the underlying mechanisms of stomatal regulation in the maximum photosynthetic efficiency of Robusta coffee trees, especially in a shade condition is necessary. Methods: This study aimed to evaluate how stomatal regulation in Robusta coffee leaves affects gas exchange under different cropping systems. The Robusta coffee trees were grown in four different cropping systems: monoculture (full-sun condition) (S1), intercropped (single row) with rubber trees (S2), intercropped (double spacing) with rubber trees (S3), and intercropped in a mixed orchard (S4). Result: The results revealed that Robusta coffee trees grown between rubber tree rows with closer spacing (S2) exhibited the largest stomata sizes. These stomata sizes had a statistically significant increase in width, length, and area (ranging from 12.04 to 14.74 µm, 19.22 to 25.55 µm, and 202.37 to 296.05 µm², respectively) compared to Robusta coffee grown in S1, S3, and S4 systems. On the other hand, Robusta coffee grown in S1 system displayed the highest stomatal density, ranging from 310 to 540 stomata/mm². Interestingly, coffee trees grown between rubber rows (S3) and in the mixed orchard (S4) exhibited both high rates of photosynthesis (9.18 and 9.35 µmol/m²/s) and photosynthetic water-use efficiency (3.78 and 5.15 mmol/mol). Notably, these values were statistically different from those observed in other planting conditions. Additionally, Robusta coffee grown in S1 system exhibited the highest canopy temperature (ranging from 30.8 to 47.4°C). It also had the lowest Fv/Fm value (ranging from 0.706 to 0.759) compared to other planting conditions. This study indicates that Robusta coffee leaves exhibited varying stomatal responses to changes in light and temperature depending on the cropping system. By understanding how these leaf traits influence adaptation, we could potentially optimize Robusta coffee trees to thrive in full sun and shaded conditions, particularly within intercropping systems.

The potential of nanofibrillated cellulose from Hevea brasiliensis to produce films for bio-based packaging

Cellulose micro/nanofibril (MNFC) films are an interesting alternative to plastic-based films for application in biodegradable packaging. In this study, we aimed to produce and characterize MNFC films obtained from alkaline-pretreated rubberwood (Hevea brasiliensis) waste and Eucalyptus sp. commercial pulp. MNFC and films were evaluated regarding microstructure; crystallinity; stability; and physical, optical, mechanical, and barrier properties. A combined quality index (QI) was also calculated. Eucalyptus MNFC suspensions were more stable than H. brasiliensis. Both films had a hydrophobic surface (>90°) and high grease resistance (oil kit 12). H. brasiliensis films had lower transparency (26.4 %) and high crystallinity (∼89 %), while Eucalyptus films had lower permeability and higher mechanical strength. The QI of MNFC was 51 ± 5 for H. brasiliensis and 55 ± 4 for Eucalyptus, showing that both types of raw material have potential for application in the packaging industry and in the reinforcement of composites, as well as for high value-added applications in products made from special materials.

Integrative analysis of transcriptome and metabolome reveals how ethylene increases natural rubber yield in Hevea brasiliensis.

Hevea brasiliensis is an important cash crop with the product named natural rubber (NR) for markets. Ethylene (ET) is the most effective yield stimulant in NR production but the molecular mechanism remains incomplete. Here, latex properties analysis, transcriptome analysis, and metabolic profiling were performed to investigate the mechanism of NR yield increase in four consecutive tappings after ET stimulation. The results revealed that sucrose and inorganic phosphate content correlated positively with dry-rubber yield and were induced upon ET stimulation. Stimulation with ET also led to significant changes in gene expression and metabolite content. Genes involved in phytohormone biosynthesis and general signal transduction as well as 51 transcription factors potentially involved in the ET response were also identified. Additionally, KEGG annotation of differentially accumulated metabolites suggested that metabolites involved in secondary metabolites, amino-acid biosynthesis, ABC transporters, and galactose metabolism were accumulated in response to ET. Integrative analysis of the data collected by transcriptomics and metabolomics identified those differentially expressed genes and differentially accumulated metabolites are mainly involved in amino-acid biosynthesis and carbohydrate metabolism. Correlation analysis of genes and metabolites showed a strong correlation between amino-acid biosynthesis during ET stimulation. These findings provide new insights into the molecular mechanism underlying the ET-induced increase in rubber yield and further our understanding of the regulatory mechanism of ethylene signaling in rubber biosynthesis.

The versatile plant probiotic bacterium Bacillus velezensis SF305 reduces red root rot disease severity in the rubber tree by degrading the mycelia of Ganoderma pseudoferreum1

Natural rubber is an indispensable material of strategic importance that has critical applications in industry and the military. However, the development of the natural rubber industry is impeded by the red root rot disease of rubber trees caused by Ganoderma pseudoferreum, which is one of the most devastating diseases in the rubber tree growing regions in China. To combat this disease, we screened the antifungal activity of 223 candidate bacterial strains against G. pseudoferreum, and found that Bacillus velezensis strain SF305 exhibited significant antifungal activity against G. pseudoferreum. B. velezensis SF305 had a nearly 70% efficacy against the red root rot disease of rubber trees with the therapeutic treatment (Tre), while it exhibited over 90% protection effectiveness with the preventive treatment (Pre). The underlying biocontrol mechanism revealed that B. velezensis SF305 could reduce the disease severity of red root rot by degrading the mycelia of G. pseudoferreum. An antiSMASH analysis revealed that B. velezensis SF305 contains 15 gene clusters related to secondary metabolite synthesis, 13 of which are conserved in species of B. velezensis, but surprisingly, B. velezensis SF305 possesses 2 unique secondary metabolite gene clusters. One is predicted to synthesize locillomycin, and the other is a novel nonribosomal peptides synthetase (NRPS) gene cluster. Genomic analysis showed that B. velezensis SF305 harbors genes involved in motility, chemotaxis, biofilm formation, stress resistance, volatile organic compounds (VOCs) and synthesis of the auxin indole-3-acetic acid (IAA), suggesting its plant growth-promoting rhizobacteria (PGPR) properties. B. velezensis SF305 can promote plant growth and efficiently antagonize some important phytopathogenic fungi and bacteria. This study indicates that B. velezensis SF305 is a versatile plant probiotic bacterium. To the best of our knowledge, this is the first time a B. velezensis strain has been reported as a promising biocontrol agent against the red root rot disease of rubber trees.