Search Results (7)

Tapping panel dryness (TPD) and tapping panel necrosis (TPN) are syndromes that reduce the yield of rubber trees. Their causes are associated with factors such as clone type, tapping system, and environmental stress and are potentially linked to nutrient deficiencies. This study aimed to investigate the causes of these disorders, with particular focus on their relationship with nutrient fluctuations in plant tissues. The experiment was conducted at rubber plantations owned by local farmers in Pakkhat District, Bueng Kan Province, Thailand, where soil fertility is generally poor. The plantations were 14–16 years old and had been tapped for 7–9 years. Two rubber tree clones (RRIM600 and RRIT251) were used to evaluate three different tree types: healthy, TPD-affected, and TPN-affected. For each clone, five plantations were sampled. The measurements included the incidence of abnormalities; trunk girth; yield; and nutrient concentrations in the soil, top shoot, bark, and latex. The nutrient analysis focused on nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and boron (B). The results showed that the incidence of abnormalities (both TPD and TPN) was higher in clone RRIT251 than in RRIM600. Yield was reduced in trees affected by TPD and was dramatically reduced in those affected by TPN. In RRIT251 trees affected by TPD, the lowest concentrations of K, Ca, and B were found in the bark, along with the lowest Ca concentration in the top shoot. These findings indicate that RRIT251 is more susceptible to bark necrosis than RRIM600 and that reductions in K, Ca, and B may be associated with development of the syndromes. Full article

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. Full article

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. Full article

Glutaredoxins (GRXs) are a class of small oxidoreductases which modulate various biological processes in plants. Here, we isolated a GRX gene from the rubber tree (Hevea brasiliensis Müll. Arg.), named as HbSRGRX1, which encoded 107 amino acid residues with a CPYC active site. Phylogenetic analysis displayed that HbSRGRX1 was more correlated with GRXs from Manihot esculenta Crantz. and Ricinus communis L. HbSRGRX1 was localized in the nuclei of tobacco cells, and its transcripts were preferentially expressed in male flowers and in the high-yield variety Reyan 7-33-97 with strong resistance against cold. The expression levels of HbSRGRX1 significantly decreased in tapping panel dryness (TPD) trees. Furthermore, HbSRGRX1 was regulated by wounding, hydrogen peroxide (H₂O₂), and multiple hormones. Altogether, these results suggest important roles of HbSRGRX1 in plant development and defense response to TPD and multiple stresses. Full article

Ethephon, an ethylene releaser, is used to stimulate latex production in Hevea brasiliensis. Ethylene induces many functions in latex cells including the production of reactive oxygen species (ROS). The accumulation of ROS is responsible for the coagulation of rubber particles in latex cells, resulting in the partial or complete stoppage of latex flow. This study set out to assess biochemical and histological changes as well as changes in gene expression in latex and phloem tissues from trees grown under various harvesting systems. The Tapping Panel Dryness (TPD) susceptibility of Hevea clones was found to be related to some biochemical parameters, such as low sucrose and high inorganic phosphorus contents. A high tapping frequency and ethephon stimulation induced early TPD occurrence in a high latex metabolism clone and late occurrence in a low latex metabolism clone. TPD-affected trees had smaller number of laticifer vessels compared to healthy trees, suggesting a modification of cambial activity. The differential transcript abundance was observed for twenty-seven candidate genes related to TPD occurrence in latex and phloem tissues for ROS-scavenging, ethylene biosynthesis and signalling genes. The predicted function for some Ethylene Response Factor genes suggested that these candidate genes should play an important role in regulating susceptibility to TPD. Full article

Increasing demand for natural rubber (NR) calls for an increase in latex yield and also an extension of rubber plantations in marginal zones. Both harvesting and abiotic stresses lead to tapping panel dryness through the production of reactive oxygen species. Many microRNAs regulated during abiotic stress modulate growth and development. The objective of this paper was to study the regulation of microRNAs in response to different types of abiotic stress and hormone treatments in Hevea. Regulation of MIR genes differs depending on the tissue and abiotic stress applied. A negative co-regulation between HbMIR398b with its chloroplastic HbCuZnSOD target messenger is observed in response to salinity. The involvement of MIR gene regulation during latex harvesting and tapping panel dryness (TPD) occurrence is further discussed. Full article

Tapping panel dryness (TPD) syndrome is one of the latex yield affecting factors in the rubber tree (Hevea brasiliensis Mull. Arg.). Therefore, identification of a DNA marker will be highly useful for screening progenies in breeding programs. The major goal of this study was to detect genetic variations and/or identification of gene fragments among 37 Hevea clones by the random amplified polymorphic DNA “fingerprinting” technique. Different levels of DNA polymorphism were detected with various primers and a distinct polymorphic band (2.0 kb) was obtained with OPA-17 primer. It was cloned into a plasmid vector for further sequence characterization and the nucleotide sequence shows homology with a novel putative plant thymidine kinase (TK) gene, designated as HbTK (Hevea brasiliensis thymidine kinase; GenBank accession number AY130829). The protein HbTK has 67%, 65%, 64%, and 63% similarity to TK genes of Medicago, Oryza, Arabidopsis, and Lyco-persicon, respectively, and it was highly conserved in all species analyzed. The predicted amino acid sequence contained conserved domains of TK proteins in the C-terminal half. Southern blot analysis indicated that HbTK is one of the members of a small gene family. Northern blot results revealed that the expression of the HbTK gene was up-regulated in mature bark tissues of the healthy tree while it was down-regulated in the TPD-affected one. These results suggest that this gene may play important roles in maintaining active nucleotide metabolism during cell division at the tapped site of bark tissues in the healthy tree under stress (tapping) conditions for normal latex biosynthesis. Full article