General Conference abstract: International Symposium on Physiological Processes in Roots of Woody Plants, USA/online, July 10-14 2022


Philipp Rüter, Thomas Debener, Jarosław Tyburski, Adriana Carolina Aurori, Ellen De Keyser, Emmy Dhooghe and Traud Winkelmann

Oral presentation

The ‘RootsPlus’ project is a European collaboration between research institutions in Belgium, Germany, Poland and Romania and two companies. Using natural transformation with Rhizobium rhizogenes wildtype strains, a new breeding technology shall be developed in order to address three aims: (1) generation of drought tolerant plants, (2) generation of rootstocks with tolerance against replant disease and (3) reduction of chemical plant growth regulators by generation of compact plants. The plant species under investigation are apple, chrysanthemum, sunflower and rose.

Natural strains of Rhizobium rhizogenes contain a unique Ri plasmid (which includes the rol genes) that allows them to transfer and integrate the T-DNA into the plant genome. The result is an enhanced root formation (so-called hairy roots). Subsequently, Ri plants can be regenerated in vitro from the hairy roots. The presence of the Ri genes in these plants results in a typical phenotype with a more pronounced root system and more compact growth, as well as changes in flowering and leaf morphology. In many countries, these natural transformants do not fall under the regulations of GMOs (genetically modified organisms).

These Ri plants are 'pre-breeding' material and can result in commercial cultivars with a stronger root system combined with all the specific quality characteristics.

One major objective is to investigate the genetic basis of the transformability in rose. Using a GWAS (genome wide association study), genes will be identified that are important for transformability by R. rhizogenes. A panel of around 100 cut and garden roses for which the genetic data is already present in form of the 68k Axiom WagRhSNP chip will be transformed with a bacterial strain carrying the reporter gene GFP (green fluorescent protein) and thus deliver the phenotyping data by detection of fluorescent hairy roots. In preparation of this high-throughput transformation approach, the transformation protocol was optimized by testing different explant types and wounding methods for rose genotypes. Sonication assisted transformation of leaf blades was established and the currently running rose phenotyping shows clear genotypic differences in the transformation efficiency. Explants from some genotypes developed no roots at all, whereas in other genotypes approximately 70 % of the explants were able to regenerate fluorescent roots.