A method for Agrobacterium tumefaciens-mediated transformation of Pinus radiata cotyledon explants was developed using commercially available open-pollinated seed. Pinus radiata is the most widely planted commercial conifer species in the Southern Hemisphere. Reports on transformation of this species have relied on particle bombardment of embryogenic callus derived from immature embryos. The main drawback to the method is the small number of genotypes that are amenable to transformation and regeneration. Since more than 80% of genotypes of radiata pine can be regenerated using cotyledons from mature seed, cotyledon explants were cocultivated with A. tumefaciens strain AGL1 containing a plasmid coding for the neomycin phosphotransferase II (nptII) gene and the beta-glucuronidase (GUS) gene (uidA). Transformed shoots were selected using either geneticin or kanamycin. Critical factors for successful transformation were survival of the cotyledons after cocultivation and selection parameters. Of the 105 putative transformants that were recovered from selection media, 70% were positive for integration of the nptII gene when analysed by PCR. GUS histochemical assay for uidA expression was unreliable because of reaction inhibition by unidentified compounds in the pine needles. Further, only 4 of the 26 independent transformants characterised by PCR and Southern analysis contained an intact copy of both genes. The remaining 22 transformants appeared to have a truncated or rearranged copy of the T-DNA. It is possible that the truncation/rearrangements are due to the Cauliflower mosaic virus (CaMV) 35S promoter. Analysis of the T-DNA junction sites and sequencing of the introduced DNA will help elucidate the nature of T-DNA insertion so that genetic modification of radiata pine can be targeted effectively.

We compared the efficiency of two Agrobacterium tumefaciens strains, AGL 1 and KYRT1, for producing transgenic pea plants. KYRT1 is a disarmed strain of Chry5 that has been shown to be highly tumourigenic on soybean. The efficacies of the strains were compared using cotyledon explants from three pea genotypes and two plasmids. The peas were sourced from field-grown plants over three Southern Hemisphere summer seasons. Overall, KYRT1 was found to be on average threefold more efficient than AGL 1 for producing transgenic plants. We suggest that KYRT1 is sensitive to cocultivation temperature as the expected increase in efficiency was not achieved at high laboratory temperatures.

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Key Message Agrobacterium tumefaciens was used to transform radiata pine shoots and to efficiently produce stable genetically modified pine plants.Abstract Micropropagated shoot explants from Pinus radiata D. Don were used to produce stable transgenic plants by Agrobacterium tumefaciens-mediated transformation. Using this method any genotype that can be micropropagated could produce stable transgenic lines. As over 80% of P. radiata genotypes tested can be micropropagated, this effectively means that any line chosen for superior characteristics could be transformed. There are well-established protocols for progressing such germplasm to field deployment. Here we used open and control pollinated seed lines and embryogenic clones. The method developed was faster than other methods previously developed using mature cotyledons. PCR positive shoots could be obtain within 6 months of Agrobacterium co-cultivation compared with 12 months for cotyledon methods. Transformed shoots were obtained using either kanamycin or geneticin as the selectable marker gene. Shoots were recovered from selection, were tested and were not chimeric, indicating that the selection pressure was optimal for this explant type. GFP was used as a vital marker, and the bar gene, (for resistance to the herbicide Buster ® ) was used to produce lines that could potentially be used in commercial application. As expected, a range of expression phenotypes were identified for both these reporter genes and the analyses for expression were relatively easy.