Agrobacterium tumefaciens-mediated genetic transformation and the regeneration of transgenic plants was achieved in Hevea brasiliensis. Immature anther-derived calli were used to develop transgenic plants. These calli were co-cultured with A. tumefaciens harboring a plasmid vector containing the H. brasiliensis superoxide dismutase gene (HbSOD) under the control of the CaMV 35S promoter. The beta-glucuronidase gene (uidA) was used for screening and the neomycin phosphotransferase gene (nptII) was used for selection of the transformed calli. Factors such as co-cultivation time, co-cultivation media and kanamycin concentration were assessed to establish optimal conditions for the selection of transformed callus lines. Transformed calli surviving on medium containing 300 mg l(-1) kanamycin showed a strong GUS-positive reaction. Somatic embryos were then regenerated from these transgenic calli on MS2 medium containing 2.0 mg l(-1) spermine and 0.1 mg l(-1) abscisic acid. Mature embryos were germinated and developed into plantlets on MS4 medium supplemented with 0.2 mg l(-1) gibberellic acid, 0.2 mg l(-1) kinetin (KIN) and 0.1 mg l(-1) indole-3-acetic acid. A transformation frequency of 4% was achieved. The morphology of the transgenic plants was similar to that of untransformed plants. Histochemical GUS assay revealed the expression of the uidA gene in embryos as well as leaves of transgenic plants. The presence of the uidA, nptII and HbSOD genes in the Hevea genome was confirmed by polymerase chain reaction amplification and genomic Southern blot hybridization analyses.

Rubber tree (Hevea brasiliensis Muell. Arg.) is an important industrial crop for natural rubber production. At present, more than 9.5 million hectares in about 40 countries are devoted to rubber tree cultivation with a production about 6.5 million tons of dry rubber each year. The world supply of natural rubber is barely keeping up with a global demand for 12 million tons of natural rubber in 2020. Tapping panel dryness (TPD) is a complex physiological syndrome widely found in rubber tree plantations, which causes severe yield and crop losses in natural rubber producing countries. Currently, there is no effective prevention or treatment for this serious malady. As it is a perennial tree crop, the integration of specific desired traits through conventional breeding is both time-consuming and labour-intensive. Genetic transformation with conventional breeding is certainly a more promising tool for incorporation of agronomically important genes that could improve existing Hevea genotype. This chapter provides an Agrobacterium-mediated transformation protocol for rubber tree using immature anther-derived calli as initial explants. We have applied this protocol to generate genetically engineered plants from a high yielding Indian clone RRII 105 of Hevea brasiliensis (Hb). Calli were co-cultured with Agrobacterium tumefaciens harboring a plasmid vector containing the Hb superoxide dismutase (SOD) gene and the reporter gene used was beta-glucuronidase (GUS) gene (uidA). The selectable marker gene used was neomycin phosphotransferase (nptII) and kanamycin was used as selection agent. We found that a suitable transformation protocol for Hevea consists of a 3-d co-cultivation with Agrobacterium in the presence of 20 mM acetosyringone, 15 mM betaine HCl, and 11.55 mM proline followed by selection on medium containing 300 mg/L kanamycin. Transformed calli surviving on medium containing 300 mg/L kanamycin showed a strong GUS-positive reaction. Upon subsequent subculture into fresh media, we obtained somatic embryogenesis and germinated plantlets, which were found to be GUS positive. The integration of uidA, nptII, and HbSOD transgenes into Hevea genome was confirmed by polymerase chain reaction (PCR) as well as Southern blot analysis.

Genetic transformation and regeneration of rubber tree (Hevea brasiliensis Muell. Arg) transgenic plants with a constitutive version of an anti-oxidative stress superoxide dismutase gene

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Hevea brasiliensis (Para rubber tree) is the major source of commercial natural rubber (cis‐1,4‐polyisoprene). Rubber produced in specialized cells called laticifers is one of the most important biological molecules used for the manufacture of about 35000 products. Being a cross‐pollinated perennial tree species, genetic improvement through conventional breeding is a rather slow process. Biotechnology would play an important role in the future of the rubber industry. Plant regeneration via somatic embryogenesis using a variety of explant sources like, integumental tissues, immature anther, immature inflorescences, and leaf explants are well standardized. Many genes controlling important agronomic traits and tissue‐specific promoters have been characterized in rubber. Agrobacterium and biolistic‐mediated genetic transformation systems are well established in this crop. Thus, the basic technology for genetic manipulation of rubber plant at the cellular and molecular levels is available, making rubber a suitable crop for genetic engineering. In different laboratories, rubber plants were genetically transformed for recombinant protein production with the gene coding for human serum albumin, immunoglobulin single chain variable fragment, and TB antigen gene. Transgenic rubber plants were also produced with Mn.SOD gene to confer tolerance against a variety of environmental stresses and tapping panel dryness. Attempts are also going on to enhance the rubber yield through transgenic approaches. Since, the major harvested products are not used as food material, the biosafety concerns are less for the genetically modified rubber plants.