Kalanchoë blossfeldiana naturally transformed with Rhizobium rhizogenes exhibits superior root phenotype

Plant transformation with root oncogenic loci (rol) genes and open reading frames (ORFs) from Rhizobium rhizogenes have not yet targeted the underground root phenotype of these transformants. Hence, there is a need to develop plants with more efficient root system architecture (RSA). Here, RSA was assessed in naturally transformed (NT) and single rol/ORF Kalanchoë blossfeldiana 'Molly' lines in an aeroponic growth system combined with gene expression analysis. Three NT lines; 306, 324 and 331; exhibited better-developed RSA with longer roots and increased root biomass. In line 306, longest root was 6.3 ± 0.3 cm while WT had 4.8 ± 0.1 cm. However, root length of all overexpressing lines was ca. 30% shorter than WT. Root fresh weight of NT lines was 4.5-fold higher than WT. The expression of rolB, ∆ORF13a and ORF14 in the leaves of overexpressing lines was many folds higher than in NT lines. Increased expression of ∆ORF13a and ORF14 in leaves and roots may contribute more to a stronger compact phenotype than previously assumed. The moderate compact phenotype of NT lines combined with improved RSA compared to the overexpressing lines and WT strongly indicate that the use of R. rhizogenes has great potential to produce Kalanchoë phenotypes with enhanced RSA.