Agrobacterium rhizogenes–induced Altered Morphology and Physiology in Rubber Dandelion after Genetic Transformation

Abstract

Agrobacterium rhizogenes transformation is a more rapid method of obtaining transgenic and edited rubber dandelion (Taraxacum kok-saghyz) plants than Agrobacterium tumefaciens. The hairy root rol genes are present alongside transgenes after transformation, and they change the morphology of rubber dandelion significantly. Although these rol genes are useful visual markers indicating successful transformation of rubber dandelion, they modify the phenotype induced by the target transgenes and are ultimately detrimental to agronomic traits. Fortunately, the rol genes can be removed by conventional plant breeding because they segregate in progeny separately from the targeted transgenes. However, it is preferable to have preliminary identification of promising effects induced by transgenes or gene edits before rol gene removal so that only the best plants are used for breeding. Therefore, the goal of this research was to characterize rol– and rol+ plant morphology so that, in the future, rol+ transgene+ plants can be easily distinguished from rol+ transgene– plants. This requires that rol gene–induced morphological changes and simply assayed physiological traits are first characterized thoroughly so that transgene changes may be observed. Taproot formation is reduced or eliminated in rubber dandelion by rol genes, and rol-induced hairy roots are identifiable easily because they grow shallowly in potting soil, so only partial unearthing is needed. Both leaf and flower numbers are increased by rol genes, but leaves and flowers are smaller than in rubber dandelion wild type with longer stalks. The rosette doming phenotype caused by the induction of a large number of leaf primordia is obvious in rooted plants as young as 1 month old. Photosynthetic rates are reduced significantly in rol+ plants, although growth is not. An accurate description of the morphology of rubber dandelion after A. rhizogenes transformation may allow for initial selection of promising transformed plants before confirmation with polymerase chain reaction, by phenotypic comparison of plants expressing transgenes and the rol gene, with those only expressing the rol gene.