Tapping Panel Research Articles

Genome-Wide Identification and Expression Profile Analysis of the Phenylalanine Ammonia-Lyase Gene Family in Hevea brasiliensis.

The majority of the world's natural rubber comes from the rubber tree (Hevea brasiliensis). As a key enzyme for synthesizing phenylpropanoid compounds, phenylalanine ammonia-lyase (PAL) has a critical role in plant satisfactory growth and environmental adaptation. To clarify the characteristics of rubber tree PAL family genes, a genome-wide characterization of rubber tree PALs was conducted in this study. Eight PAL genes (HbPAL1-HbPAL8), which spread over chromosomes 3, 7, 8, 10, 12, 13, 14, 16, and 18, were found to be present in the genome of H. brasiliensis. Phylogenetic analysis classified HbPALs into groups I and II, and the group I HbPALs (HbPAL1-HbPAL6) displayed similar conserved motif compositions and gene architectures. Tissue expression patterns of HbPALs quantified by quantitative real-time PCR (qPCR) proved that distinct HbPALs exhibited varying tissue expression patterns. The HbPAL promoters contained a plethora of cis-acting elements that responded to hormones and stress, and the qPCR analysis demonstrated that abiotic stressors like cold, drought, salt, and H2O2-induced oxidative stress, as well as hormones like salicylic acid, abscisic acid, ethylene, and methyl jasmonate, controlled the expression of HbPALs. The majority of HbPALs were also regulated by powdery mildew, anthracnose, and Corynespora leaf fall disease infection. In addition, HbPAL1, HbPAL4, and HbPAL7 were significantly up-regulated in the bark of tapping panel dryness rubber trees relative to that of healthy trees. Our results provide a thorough comprehension of the characteristics of HbPAL genes and set the groundwork for further investigation of the biological functions of HbPALs in rubber trees.

Integrated physiology, transcriptome and proteome analyses highlight the potential roles of multiple hormone-mediated signaling pathways involved in tapping panel dryness in rubber tree

Currently, one of the most serious threats to rubber tree is the tapping panel dryness (TPD) that greatly restricts natural rubber production. Over-tapping or excessive ethephon stimulation is regarded as the main cause of TPD occurrence. Although extensive studies have been carried out, the molecular mechanism underlying TPD remains puzzled. An attempt was made to compare the levels of endogenous hormones and the profiles of transcriptome and proteome between healthy and TPD trees. Results showed that most of endogenous hormones such as jasmonic acid (JA), 1-aminocyclopropanecarboxylic acid (ACC), indole-3-acetic acid (IAA), trans-zeatin (tZ) and salicylic acid (SA) in the barks were significantly altered in TPD-affected rubber trees. Accordingly, multiple hormone-mediated signaling pathways were changed. In total, 731 differentially expressed genes (DEGs) and 671 differentially expressed proteins (DEPs) were identified, of which 80 DEGs were identified as putative transcription factors (TFs). Further analysis revealed that 12 DEGs and five DEPs regulated plant hormone synthesis, and that 16 DEGs and six DEPs were involved in plant hormone signal transduction pathway. Nine DEGs and four DEPs participated in rubber biosynthesis and most DEGs and all the four DEPs were repressed in TPD trees. All these results highlight the potential roles of endogenous hormones, signaling pathways mediated by these hormones and rubber biosynthesis pathway in the defense response of rubber trees to TPD. The present study extends our understanding of the nature and mechanism underlying TPD and provides some candidate genes and proteins related to TPD for further research in the future.

Evaluation of Four Yield Stimulants on Hevea brasiliensis Yield

Latex yield stimulants, such as ethephon (2-chloroethylphosphonic acid), are widely utilised in the rubber industry to extend latex flow, ultimately improving latex yield. In this study, which lasted 44 months, the efficacy of three promising liquid stimulants (referred to as Products A, B, and D) was compared with Product C which is the common stimulation product used currently. Overall, all tested latex stimulation products demonstrated the ability to increase latex yield per tapping by 75 to 89 grammes per tree per tapping (g/t/t) or 50 to 78 per cent during the months of stimulation. However, on a long-term basis, when the yields of stimulated and non-stimulated (wintering) months were taken into account, the yield per tapping of stimulated trees increased by 11 to 18 g/t/t or 32 to 51 per cent. Notably, Product A, when applied three times a month, showed the highest incidence of tapping panel dryness (TPD) compared to the Control and Product D treatments, where no TPD was observed. The cost-benefit analysis showed that Product C was the most economically viable option, costing only RM 0.10 per kilogramme of latex yield, in contrast to the other stimulants, which ranged from RM 0.19 to RM 2.15 per kilogramme of latex yield. Keywords: Natural rubber, panel dryness, rubber production, latex yield stimulants.

Construction and analysis of the tapping panel dryness-related lncRNA/circRNA-miRNA-mRNA ceRNA network in latex of Hevea brasiliensis

Tapping panel dryness (TPD) results in a severe reduction in latex yield in Hevea brasiliensis. However, the molecular regulatory mechanisms of TPD occurrence are still largely unclear. In this study, whole-transcriptome sequencing was carried out on latex from TPD and healthy trees. In total, 7078 long noncoding RNAs (lncRNAs), 3077 circular RNAs (circRNAs), 4956 miRNAs, and 25041 mRNAs were identified in latex, among which 435 lncRNAs, 68 circRNAs, 320 miRNAs, and 1574 mRNAs were differentially expressed in the latex of TPD trees. GO and KEGG analyses indicated that plant hormone signal transduction, MAPK signaling pathway, and ubiquitin-mediated proteolysis were the key pathways associated with TPD onset. Phytohormone profiling revealed significant changes in the contents of 28 hormonal compounds, among which ACC, ABA, IAA, GA, and JA contents were increased, while SA content was reduced in TPD latex, suggesting that hormone homeostasis is disrupted in TPD trees. Furthermore, we constructed a TPD-related competitive endogenous RNA (ceRNA) regulatory network of lncRNA/circRNA-miRNA-mRNA with 561 edges and 434 nodes (188 lncRNAs, 5 circRNAs, 191 miRNAs, and 50 mRNAs) and identified two hub lncRNAs (MSTRG.11908.1 and MSTRG.8791.1) and four hub miRNAs (hbr-miR156, miR156-x, miRf10477-y, and novel-m0452-3p). Notably, the lncRNA-miR156/157-SPL module containing three hubs probably plays a crucial role in TPD onset. The expression of network hubs and the lncRNA-miR156/157-SPL module were further validated by qRT-PCR. Our results reveal the TPD-associated ceRNA regulatory network of lncRNA/circRNA-miRNA-mRNA in latex and lay a foundation for further investigation of molecular regulatory mechanisms for TPD onset in H. brasiliensis.

Bark transcriptome analyses reveals molecular mechanisms involved in tapping panel dryness occurrence and development in rubber tree (Hevea brasiliensis)

Tapping panel dryness (TPD) has become the mostimportant limiting factor for increasing natural rubber yield, whereas illuminating the molecular mechanisms underlying TPD is the prerequisite for solving the problem of TPD. However, molecular mechanisms underlying TPD are largely unknown. In this study, healthy and different stages of TPD-affected rubber trees were utilized to analyze TPD for the first time. We found that the changing tendencies of key latex physiological parameters were closely related to TPD occurrence and development. To reveal the molecular mechanisms underlying TPD, we sequenced and compared bark transcriptomes among healthy rubber tree, and TPD-affected ones at initial and advanced stages. In total, 8607 genes were identified as TPD-related genes in contrast to healthy rubber tree. According to gene expression profiles, the five samples were divided into three groups including healthy rubber tree, and TPD-affected rubber tree in the initial and advanced stages, which was consistent with the stages of TPD occurrence and development. Interestingly, only asmall proportionof the TPD-related genes were constantly down- or up-regulated with TPD occurrence and development. The TPD-related genes in KEGG pathways significantly enriched were closely associated with protein metabolism, cell division and differentiation, PCD, stress responses, terpene biosynthesis, and various metabolism processes. Moreover, overexpression of HbAPX2 identified as a TPD-related gene enhanced oxidative stress tolerance in S. cerevisiae. The typical symptoms of TPD, partial or complete dry zone (no latex flow) on tapping panel, might attribute to lower IPP available for rubber biosynthesis, and downregulation of the genes in post-IPP steps of rubber biosynthesis and the genes involved in latex flow. Our results not only provide new insights into molecular mechanisms underlying TPD occurrence and development but also contribute to developing effective measures to control TPD in rubber trees.

Determination of antioxidant enzymes level in healthy and tapping panel dryness (TPD) syndrome affected bark tissues of rubber tree (Hevea brasiliensis Muell. Arg.)

Oxidative stress may lead to overproduction of reactive oxygen species (ROS) which are highly toxic ultimately cause stimulation of antioxidant enzymes and damages to proteins, lipids, carbohydrates and DNA molecules in bark tissue of Hevea brasiliensis during onset of Tapping panel dryness syndrome (TPD). In this study, Antioxidant enzymes level in bark tissues of seven different healthy and TPD affected clones of Hevea brasiliensis namely RRII 105, PB 217, PB 235, PB 285, PB 5/51, PCK2 and GT1 was determined to monitor TPD occurrence. The results revealed that increased level of antioxidant enzymes activity was noticed in bark tissues of TPD affected clones while it was found to be low in healthy clones. Maximum level of superoxide dismutase (SOD) activity noticed was 0.634 U/mg FW in healthy PB 5/51 clone compared with its TPD affected clone. The CAT activity was also found to be high in healthy PB 5/51 clone (1.988 U/mg) than TPD affected clone. In the case of peroxidase (POX) activity, it was found to be low in all healthy clones while the activity was significantly increased in TPD affected clones and maximum activity was noticed in PCK2 followed by PB285. Antioxidant enzymes level was also determined by native PAGE analysis and its results showed that isoenzymes of SOD and POX banding pattern are directly correlated with biochemical assays activity. This research correlates the activities of antioxidant enzymes between healthy and TPD affected clones and paves the path to understand the role of SOD, CAT and POX during onset of TPD and leads to future genetic studies on antioxidant enzymes and its genes in Hevea brasiliensis.

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.

Multi-level thresholding image segmentation for rubber tree secant using improved Otsu's method and snake optimizer.

The main disease that decreases the manufacturing of natural rubber is tapping panel dryness (TPD). To solve this problem faced by a large number of rubber trees, it is recommended to observe TPD images and make early diagnosis. Multi-level thresholding image segmentation can extract regions of interest from TPD images for improving the diagnosis process and increasing the efficiency. In this study, we investigate TPD image properties and enhance Otsu's approach. For a multi-level thresholding problem, we combine the snake optimizer with the improved Otsu's method and propose SO-Otsu. SO-Otsu is compared with five other methods: fruit fly optimization algorithm, sparrow search algorithm, grey wolf optimizer, whale optimization algorithm, Harris hawks optimization and the original Otsu's method. The performance of the SO-Otsu is measured using detail review and indicator reviews. According to experimental findings, SO-Otsu performs better than the competition in terms of running duration, detail effect and degree of fidelity. SO-Otsu is an efficient image segmentation method for TPD images.

Agromorphological Characterization of a Rubber Tree-Teak Agroforestry System in Central Côte d’Ivoire

Aims: Faced with environmental issues, soil degradation and the scarcity of arable land, farmers are adopting several cropping practices, including agroforestry. It is in this context that a study entitled “Agromorphological characterization of a rubber tree-teak agroforestry system in central Côte d’Ivoire” was carried out in order to assess the effects of this crop combination on the agromorphological parameters of these crops.
 Place and Duration of Study: The study was carried out in Lomo Sud, a village in the city of Toumodi (central Côte d’Ivoire) from February to August 2022.
 Methodology: Two experiments were carried out on two plots, a rubber tree one and a teak one. On the rubber tree plot, ten treatments were defined depending on their proximity to teak. On the teak plot, seven treatments were determined depending on their proximity to rubber trees. On each plot, the experimental design was in one tree plot design. The parameters taken into account in the study on rubber trees were stand, girth, rubber yield and rate of tapping panel dryness. For teak, the parameters assessed were stand, girth, straightness, cylindricity, branching, pruning and health condition.
 Results: For rubber trees, the results showed that teak negatively influenced the number of rubber trees under tapping, growth and rubber yield, which were reduced by 125, 18 and 110%, respectively. For teak, the results showed that rubber trees positively influenced the growth, straightness, branching and pruning of teak.
 Conclusion: The rubber tree-teak agroforestry system assessed in central Côte d'Ivoire is beneficial for teak but detrimental to rubber trees.

Computational Biology and Machine Learning Approaches Identify Rubber Tree (Hevea brasiliensis Muell. Arg.) Genome Encoded MicroRNAs Targeting Rubber Tree Virus 1

Tapping panel dryness (TPD), a complex physiological syndrome associated with the rubber tree (Hevea brasiliensis Muell. Arg.), causes cessation of latex drainage upon tapping and thus threatens rubber production. Rubber tree virus 1 (RTV1) is a novel positive-sense single-stranded RNA virus from the Betaflexiviridae (genus Capillovirus), which has been established to cause TPD. MicroRNAs (miRNAs) play an important role in the interplay between viruses and host cells. In this study, we identified the rubber tree genome-encoded miRNAs and their therapeutic targets against RTV1. We applied computational algorithms to predict target binding sites of rubber tree miRNAs potentially targeting RTV1 RNA genome. Mature rubber-tree miRNAs are retrieved from the miRBase database and are used for hybridization of the RTV1 genome. A total of eleven common rubber-tree miRNAs were identified based on consensus genomic positions. The consensus of four algorithms predicted the hybridization sites of the hbr-miR396a and hbr-miR398 at common genomic loci (6676 and 1840), respectively. A miRNA-regulatory network of rubber tree was constructed with the RTV1— ORFs using Circos, is illustrated to analyze therapeutic targets. Overall, this study provides the first computational evidence of the reliable miRNA–mRNA interaction between specific rubber tree miRNAs and RTV1 genomic RNA transcript. Therefore, the predicted data offer valuable evidence for the development of RTV1-resistant rubber tree in the future. Our work suggests that similar computational host miRNA prediction strategies are warranted for identification of the miRNA targets in the other viral genomes.

Influence of Tapping Depth on Rubber Yield and Tapping Quality in Rubber Tree Plantations in Southeastern Côte d'Ivoire

Aims: Rubber tree (Hevea brasiliensis Muell Arg.) is the main source of natural rubber. Its cultivation generates significant income for several companies and farmers around the world. However, its exploitation is threatened by the considerable drop in rubber yield which is due to the ignorance of tapping criteria in particular the optimal tapping depth. This study aims at improving rubber yield.
 Place and Duration of Study: The study was carried out in agro-industrial plantations of rubber tree in southeastern Côte d'Ivoire from June 2020 to January 2021.
 Methodology: The study took place in two phases: the first consisted in assessing the tapping depth of the plantations and the second in studying the influence of the different tapping depths on rubber yield and tapping quality. The first study was carried out with 347 tappers in 954 tapping tasks. The second study focused on 4 rubber tree clones (PB217, IRCA 41, IRCA 230 and IRCA18) belonging to the three metabolic activity classes. These clones were subjected to 4 treatments (T0: tapping to a depth of 0 to 1.5 mm; T1: tapping to a depth of 1 to 2 mm; T2: tapping to a depth of 1 to 1.5 mm, T3: tapping to a depth of 1.5 to 2 mm) in a completely randomized block design with 4 repetitions. This comparative study was carried out on the basis of yield and tapping quality parameters (bark consumption, wounds).
 Results: The results of the first study showed that the average tapping depth of the plantations inspected is 1.44 mm in half-spiral downward tapping and 1.82 mm in a quarter-spiral upward tapping. The tapping depth is influenced by the height of the tapping panel and by the clone. The results of the second study showed that tapping depth influences rubber yield and tapping quality. Indeed, tapping to a depth between 1 and 1.5 mm from the cambium induces the most significant yields but causes poor tapping quality. In contrast, tapping to a depth between 1 and 2 mm from the cambium gives lower yields but makes it possible to show better tapping quality.
 Conclusion: The tapping depth is influenced by the height of the tapping panel and by the clone. The tapping depth influences rubber yield and tapping quality.

Dynamic analysis of Tapping Panel Dryness in Hevea brasiliensis reveals new insights on this physiological syndrome affecting latex production

Tapping Panel Dryness (TPD) is a physiological disorder affecting natural rubber production in Hevea brasiliensis. TPD is associated with clonal susceptibility and overexploitation of rubber trees. Most studies are based on a binary point view of the absence or presence of TPD. This study sets out to characterize the dynamic of the TPD onset through the monthly monitoring of the dry cut length. This reveals the presence of dry spots on the tapped panel of any trees. The frequency of these dry spots increases dramatically in trees developing high level of TPD. Brown bast is an irreversible form of TPD. Brown bast is correlated to a high level of dry cut length. Application of an intensive harvesting system induces early TPD occurrence, which facilitates the study of TPD. Among latex diagnosis parameters, only sucrose content is significantly associated with TPD. Other parameters are more prone to environmental effects and are not reliable as physiological markers. These findings explain the contradictory conclusions of some papers. This study suggests to use intensive harvesting system and monitor the dry cut length for genetic analysis of TPD.

Analysis of reduced and oxidized antioxidants in Hevea brasiliensis latex reveals new insights into the regulation of antioxidants in response to harvesting stress and tapping panel dryness

Latex diagnosis (LD) is applied to optimize the natural rubber production and prevent tapping panel dryness (TPD), a physiological syndrome affecting latex production in Hevea brasiliensis. The reduced thiol content (RSH) is one of the biochemical parameters associated with the risk of TPD. However, RSH is difficult to interpret because of the influence of the environment. In order to better understand the regulation of antioxidants and to better interpret RSH, a key parameter of LD, this study analysed in latex both oxidised and reduced forms of ascorbic acid (AsA) and glutathione, and their cofactors as well as other latex diagnosis parameters in response to harvesting stress (tapping and ethephon stimulation) and TPD occurrence. The content of antioxidants in latex had a high variability among five rubber clones. The concentration in AsA was about ten times higher than GSH in laticifer, GSH accounting for about 50% of RSH. For short-term harvesting stress, RSH increased with tapping frequency and ethephon stimulation. TPD is associated with high latex viscosity and bursting of lysosomal particles called lutoids, as well as for several rubber clones with lower RSH and GSH contents. These results suggest that a high level of RSH shows the capacity of laticifer metabolism to cope with harvesting stress, while a drop in RSH is the sign of long stress related to lower metabolic activity and TPD occurrence. RSH remains an essential physiological parameter to prevent TPD when associated with reference data under low and high harvesting stress. This study paves the way to understand the role of AsA and GSH, and carry out genetic studies of antioxidants.

Effect of Early Upward Tapping on Rubber Productivity of Clone PB 260 of the High Metabolic Activity Class

In order to evaluate the effect of early upward tapping on rubber productivity of rubber trees and to determine its proportion relative to downward tapping, a study was conducted at SAPH Divo on the PB 260 clone of the fast metabolic activity class. The experimental set-up was a Fisher block with seven treatments and three replications. Tapping was carried out in d3 with 6 stimulations. Three upward tapping times at 6, 7 and 8 years, each coupled with two concentrations of the stimulating paste 2.5 and 5% of Ethephon and a downwardly tapped control stimulated with 5% of Ethephon were tested. The data collected were for rubber production, isodiametric growth, tapping panel dryness susceptibility and tree physiological profile. The results showed that the different treatments tapped in upward at 6, 7 and 8 years of age significantly improved the productivity of the PB 260 clone relative to the control by downward for nine years. All treatments combined, rubber productivity (4723 kg.ha-1.yr-1) and radial vegetative growth (3.8 cm.yr-1) were good. The gain in rubber productivity of the early upward tapping compared to the downward tapping was 42%. The tapping panel dryness rate was low at 2.6% and the physiological profile of the trees was well balanced. Our results suggest that PB 260, and therefore metabolically active clones, can be tapped in early upward tapping, especially at 6 years of age.

Effects of Planting Density on Growth and Yield Attributes of Rubber Trees (Hevea brasiliensis)

This study aimed to identify rubber clones, suitable for rubber-timber production. An experiment was established in randomized complete block design to evaluate the effects of two different planting densities on girth, girth increment, bark thickness, latex yield per tapping per tree (g/t/t), incident of tapping panel dryness disease, and wood potential of nine rubber clones, including RRIV 2, RRIV 3, RRIV 4, RRIV 5, RRIV 107, PB 235, PB 260, PB 330, and RRIC 121. Data of girth, girth increment, bark thickness were collected in the 7th year, prior to opening for tapping, and 17th year of planting. In contrast, data of latex yield were collected in the 3rd and the 11th tapping year, and wood potential was compared based on the data collected in the 11th tapping year. As a result, there were no significant interactions between clones and planting density in girth growth, latex yield, tapping panel dryness and bark thickness, and the first tapping panel (BO-1). There were no significant interactions between clone and planting density on girth growth, latex yield, tapping panel dryness, and bark thickness when these clones were tapped on the first tapping panel (BO- 1). Meanwhile, there were significant interactions between clones and planting density on girth growth, girth increment, and latex yield when the trees were tapped on the second tapping panel (BO-2). Statistical comparison of mean diameters at breast height and bole volume per tree of the same clones at two different planting densities showed that most of the studied clones gave significant differences. However, no significant differences resulted in the statistical comparison of the mean bole height of the same clones at two different planting densities. The total bole volume per hectare of all studied clones was larger at high planting density than at normal planting density. However, the bole volume per tree at high planting density was smaller than that at normal planting density. Clone RRIC 121 could be considered a suitable clone for latex and timber productions. The favorable planting density for commercial timber production is high.

Latex Harvesting Technologies Adapted to Hevea brasiliensis Muell Clones GT 1; RRIC 100 and BPM 24 Arg. (Euphorbiaceae) belonging to the Moderate Metabolism Class in the Socio-economic Context of Côte d'Ivoire

Improving the productivity of rubber trees has always been a major concern for rubber farmers. The majority of growers opt for overexploitation of the trees. This disturbs the physiological balance of the rubber trees, which leads to the recrudescence of tapping panel dryness and rather to a drop in production. To solve this problem, the present study proposes to define a latex harvesting technology (or technologies) for the moderate metabolism clone class that will allow the improvement of plantation yield and the increase of the economic life of the trees. To achieve this, the GT 1, RRIC 100 and BPM 24 clones of the moderate metabolism class were used as plant material. The results showed that the reduction in tapping frequency had no negative effect on the vegetative state of the trees. This reduction was compensated by a high number of annual stimulations, which resulted in high dry rubber production. Analysis of dry rubber production, radial rubber growth and tapping panel dryness rate indicates that the moderate metabolic class clones performed better with the latex harvesting technologies S/2 d3 6d/7 ET2.5% Pa1(1) 6/y; S/2 d4 6d/7 ET2.5% Pa1(1) 6/y and S/2 d5 6d/7 ET2.5% Pa1(1) 1.

Genome-wide identification of lncRNAs, miRNAs, mRNAs and their regulatory networks involved in tapping panel dryness in rubber tree (Hevea brasiliensis).

Noncoding RNAs (ncRNAs) play pivotal roles in various biological processes in plants. However, the role of ncRNAs in tapping panel dryness (TPD) of rubber tree (Hevea brasiliensis Muell. Arg.) is largely unknown. Here, the whole transcriptome analyses of bark tissues from healthy and TPD trees were performed to identify differentially expressed long ncRNAs (DELs), microRNAs/miRNAs (DEMs), genes (DEGs) and their regulatory networks involved in TPD. A total of 263 DELs, 174 DEMs and 1574 DEGs were identified in the bark of TPD tree compared with that of healthy tree. Kyoto Encyclopedia of Genes and Genomes analysis revealed that most of the DEGs and targets of DELs and DEMs were mainly enriched in metabolic pathways, biosynthesis of secondary metabolites and plant hormone signal transduction. Additionally, the majority of DEGs and DELs related to rubber biosynthesis were downregulated in TPD trees. Furthermore, 98 DEGs and 44 DELs were targeted by 54 DEMs, 190 DEGs were identified as putative targets of 56 DELs, and 2 and 44 DELs were predicted as precursors and endogenous target mimics of 2 and 6 DEMs, respectively. Based on these, the DEL-DEM-DEG regulatory network involved in TPD was constructed, and 13 hub DELs, 3 hub DEMs and 2 hub DEGs were identified. The results provide novel insights into the regulatory roles of ncRNAs underlying TPD and lay a foundation for future functional characterization of long ncRNAs, miRNAs and genes involved in TPD in rubber tree.

Transcriptome analysis of Par\xe1 rubber tree (H. brasiliensis) seedlings under ethylene stimulation

BackgroundNatural rubber (cis-1,4-polyioprene, NR) is an indispensable industrial raw material obtained from the Pará rubber tree (H. brasiliensis). Natural rubber cannot be replaced by synthetic rubber compounds because of the superior resilience, elasticity, abrasion resistance, efficient heat dispersion, and impact resistance of NR. In NR production, latex is harvested by periodical tapping of the trunk bark. Ethylene enhances and prolongs latex flow and latex regeneration. Ethephon, which is an ethylene-releasing compound, applied to the trunk before tapping usually results in a 1.5- to 2-fold increase in latex yield. However, intense mechanical damage to bark tissues by excessive tapping and/or over-stimulation with ethephon induces severe oxidative stress in laticifer cells, which often causes tapping panel dryness (TPD) syndrome. To enhance NR production without causing TPD, an improved understanding of the molecular mechanism of the ethylene response in the Pará rubber tree is required. Therefore, we investigated gene expression in response to ethephon treatment using Pará rubber tree seedlings as a model system.ResultsAfter ethephon treatment, 3270 genes showed significant differences in expression compared with the mock treatment. Genes associated with carotenoids, flavonoids, and abscisic acid biosynthesis were significantly upregulated by ethephon treatment, which might contribute to an increase in latex flow. Genes associated with secondary cell wall formation were downregulated, which might be because of the reduced sugar supply. Given that sucrose is an important molecule for NR production, a trade-off may arise between NR production and cell wall formation for plant growth and for wound healing at the tapping panel.ConclusionsDynamic changes in gene expression occur specifically in response to ethephon treatment. Certain genes identified may potentially contribute to latex production or TPD suppression. These data provide valuable information to understand the mechanism of ethylene stimulation, and will contribute to improved management practices and/or molecular breeding to attain higher yields of latex from Pará rubber trees.

Relationship between the Intensity of Latex Harvesting and the Tapping Panel Dryness Expression of Clone GT 1 of Hevea brasiliensis Muell Arg in South-East Côte d'Ivoire

Tapping panel dryness is an important limiting factor in rubber productivity of Hevea brasiliensis. In order to assess the sensitivity to this syndrome, the effect of two intensive latex harvesting technologies on moderately metabolized GT1 clone, has been studied in the South-Eastern region of Côte d'Ivoire. The rubber trees were planted according to the experimental mono-tree device, "One tree one plot design" a tree constituting a repetition, and 31 trees per treatment, selected on circumference and health status criteria. The parameters measured were rubber production, circumference increase, physiological profile and tapping panel dryness sensitivity. The results showed that induction of tapping panel dryness in latex harvesting system, S/2 d/3 6d/7 ET 10 % Pa 1 (1) 1/ w) was significantly low (0.18 ± 0,22 %) than that of the control (S d/1 6d/7 unstimulated, 1.43 ± 1.45 %). Productivity of this particular system was also good (62 ± 16.32 g.a-1.s-1) and it especially has less stress that can cause physiological fatigue, or even the notch dry. Otherwise, Rubber production, radial vegetative growth, physiological parameters of the latex and the tapping panel dryness rate were influenced by the two treatments applied to GT 1. In addition, the medium and high sucrose contents (16.5 ± 3.01%) and thiol group (0.51 ± 0.13 mmol.l-1) of the latex in the treatment (S/2 d/3 6d/7 ET 10% Pa 1 (1) 1 / w), were instrumental in the response to this stimulation. The sensitivity to the tapping panel dryness is in very close linear relation with the harvest intensity of the latex to which the GT 1 clone has been subjected. These results corroborate and confirm the moderate sensitivity to the tapping panel dryness of GT 1 clone.

The variation of reactive oxygen species scavenging enzymes and related gene expressions during occurrence and recovery of rubber tree tapping panel dryness

The variation of reactive oxygen species scavenging enzymes and related gene expressions during occurrence and recovery of rubber tree tapping panel dryness