Molecular Characterization of β-1,3-Glucanase Gene in Pathogenic Fungi Tolerant and Susceptible Rubber Tree Clones

ABSTRACTβ-1,3-glucanase is a major lutoidic protein in lactiferous cells of rubber tree. It belongs to a pathogenesis-related (PR) protein family and is classified in PR2 group. It hasbeen reported that the expression of β-1,3-glucanase gene was induced by pathogenic fungi and wounding. In this research, to understand the relation of β-1,3-glucanase gene and pathogenic fungi tolerance in rubber tree, the expression pattern of β-1,3-glucanase gene was analyzed in non-infected plants of pathogenic fungi tolerance rubber tree clone (BPM24) and susceptible one (RRIM600) using quantitative real time polymerase chain reaction (qRT-PCR). In addition, the promoter of β-1,3-glucanase gene obtained from whole genome shotgun contigs in the National Center for Biotechnology Information (NCBI) database of BPM24 and RRIM600 rubber tree clones were analyzed in silico. The results showed that the expression of β-1,3-glucanase gene was significantly higher in BPM24 than RRIM600. Many cis-acting regulatory elements responsive to several hormones, biotic and abiotic stresses were found on β-1,3-glucanasepromoters. Higher number of defense responsive elements was found on the β-1,3-glucanase promoter of BPM24 than RRIM600. The knowledge obtained from this study leads to a betterunderstanding of the expression and regulation of β-1,3-glucanase gene in rubber tree which is beneficial for the improvement of rubber tree clone through pathogenic fungi resistance breeding program.Keywords: β-1,3-glucanase, Pathogenesis-related proteins, Rubber tre

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

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Differential expression of mitochondrial pyruvate dehydrogenase gene correlates with latex yield and tapping in rubber tree

Natural rubber (cis-1,4-polyisoprene) is a product of the isoprenoid biosynthesis pathway which requires an allylic pyrophosphate and isopentenyl pyrophosphate (IPP) to initiate and elongate the rubber molecule. The biosynthesis of IPP occurs via two distinct routes: the mevalonate (MVA) and methylerythritol phosphate (MEP) pathways. In this study, the expression of 34 genes related to rubber biosynthesis were compared between high and low latex yielding trees of two rubber tree clones, PB 217 and PB 260. Almost all tested genes revealed no significantly differential expression related to latex yield. Only mitochondrial pyruvate dehydrogenase (PDCE1) showed specific up-regulation in the high latex yielding trees of both tested clones. Interestingly, the expression of PDCE1 involving in the production of acetyl-CoA in mitochondria was also significantly induced by latex loss upon tapping. The increasing of acetyl-CoA and energy production may favor rubber tree to produce more latex. The in silico analysis showed that HbPDCE1 promoter contained ethylene and copper-responsive elements. Ethylene is worldwide used rubber stimulant while copper sulfate was also reported to be able to stimulate the latex yield. This suggested that HbPDCE1 may be transcriptionally regulated by these two compounds however the in vivo regulation of this gene should be further investigated

Involvement of HbPIP2;1 and HbTIP1;1 Aquaporins in Ethylene Stimulation of Latex Yield through Regulation of Water Exchanges between Inner Liber and Latex Cells in Hevea brasiliensis1[C][W]

Natural rubber is synthesized in specialized articulated cells (laticifers) located in the inner liber of Hevea brasiliensis. Upon bark tapping, the laticifer cytoplasm (latex) is expelled due to liber tissue turgor pressure. In mature virgin (untapped) trees, short-term kinetic studies confirmed that ethylene, the rubber yield stimulant used worldwide, increased latex yield, with a concomitant decrease in latex total solid content, probably through water influx in the laticifers. As the mature laticifers are devoid of plasmodesmata, the rapid water exchanges with surrounding liber cells probably occur via the aquaporin pathway. Two full-length aquaporin cDNAs (HbPIP2;1 and HbTIP1;1, for plasma membrane intrinsic protein and tonoplast intrinsic protein, respectively) were cloned and characterized. The higher efficiency of HbPIP2;1 than HbTIP1;1 in increasing plasmalemma water conductance was verified in Xenopus laevis oocytes. HbPIP2;1 was insensitive to HgCl2. In situ hybridization demonstrated that HbPIP2;1 was expressed in all liber tissues in the young stem, including the laticifers. HbPIP2;1 was up-regulated in both liber tissues and laticifers, whereas HbTIP1;1 was down-regulated in liber tissues but up-regulated in laticifers in response to bark Ethrel treatment. Ethylene-induced HbPIP2;1 up-regulation was confirmed by western-blot analysis. The promoter sequences of both genes were cloned and found to harbor, among many others, ethylene-responsive and other chemical-responsive (auxin, copper, and sulfur) elements known to increase latex yield. Increase in latex yield in response to ethylene was emphasized to be linked with water circulation between the laticifers and their surrounding tissues as well as with the probable maintenance of liber tissue turgor, which together favor prolongation of latex flow

Sucrose importation into laticifers of Hevea brasiliensis, in relation to ethylene stimulation of latex production

BACKGROUND AND AIMS: The major economic product of Hevea brasiliensis is a rubber-containing cytoplasm (latex), which flows out of laticifers (latex cells) when the bark is tapped. The latex yield is stimulated by ethylene. Sucrose, the unique precursor of rubber synthesis, must cross the plasma membrane through specific sucrose transporters before being metabolized in the laticifers. The relative importance of sucrose transporters in determining latex yield is unknown. Here, the effects of ethylene (by application of Ethrel on sucrose transporter gene expression in the inner bark tissues and latex cells of H. brasiliensis are described. METHODS: Experiments, including cloning sucrose transporters, real time RT-PCR and in situ hybridization, were carried out on virgin (untapped) trees, treated or untreated with the latex yield stimulant Ethrel. KEY RESULTS: Seven putative full-length cDNAs of sucrose transporters were cloned from a latex-specific cDNA library. These transporters belong to all SUT (sucrose transporter) groups and differ by their basal gene expression in latex and inner soft bark, with a predominance of HbSUT1A and HbSUT1B. Of these sucrose transporters, only HbSUT1A and HbSUT2A were distinctly increased by ethylene. Moreover, this increase was shown to be specific to laticifers and to ethylene application. CONCLUSION: The data and all previous information on sucrose transport show that HbSUT1A and HbSUT2A are related to the increase in sucrose import into laticifers, required for the stimulation of latex yield by ethylene in virgin trees