Potassium chloride and rare earth elements improve plant growth and increase the frequency of the Agrobacterium tumefaciens-mediated plant transformation

Plant transformation efficiency depends on the ability of the transgene to successfully interact with plant host factors. Our previous work and the work of others showed that manipulation of the activity of host factors allows for increased frequency of transformation. Recently we reported that exposure of tobacco plants to increased concentrations of ammonium nitrate increases the frequency of both homologous recombination and plant transgenesis. Here we tested the influence of KCl and salts of rare earth elements, Ce and La on the efficiency of Agrobacterium-mediated plant transformation. We found that exposure to KCl, CeCl3 and LaCl3 leads to an increase in recombination frequency in Arabidopsis and tobacco. Plants grown in the presence of CeCl3 and LaCl3 had higher biomass, longer roots and greater root number. Analysis of transformation efficiency showed that exposure of tobacco plants to 50 mM KCl resulted in similar to 6.0-fold increase in the number of regenerated calli and transgenic plants as compared to control plants. Exposure to various concentrations of CeCl3 showed a maximum increase of similar to 3.0-fold in both the number of calli and transgenic plants. Segregation analysis showed that exposure to KCl and cerium (III) chloride leads to more frequent integrations of the transgene at a single locus. Analysis of transgene intactness showed better preservation of right T-DNA border during transgene integration. Our data suggest that KCl and CeCl3 can be effectively used to improve quantity and quality of transgene integrations.