Peter Olsson

Adventitious root formation is a limiting factor for vegetative propagation in apple. The molecular mechanisms underlying the rooting process are still largely unknown and need to be extensively investigated. The Adventitious Rooting Related Oxygenase (ARRO-1) has previously been isolated from apple and has been shown to be upregulated during adventitious root induction. However, the function of this gene is still unclear. The aim of this study was to downregulate the ARRO-1 gene expression, using RNAi technique, to study the function of ARRO-1 in adventitious root formation in apple. The apple rootstock M26 was transformed with the RNAi-ARRO-1 construct. The transgenic clones, confirmed by PCR and Southern blot analysis, showed significantly reduced adventitious root formation both with microcuttings and stem discs, indicating the involvement of ARRO-1 in adventitious root formation. The transgenic clones also appeared to be more sensitive to exogenous hormones compared to the untransformed control plants, suggesting that ARRO-1 may be involved in regulating hormone homeostasis. Relative quantification of the ARRO-1 mRNA showed no obvious difference in transcript levels between untransformed control and the transformants. A possible explanation for this is that the downregulation of the ARRO-1 gene might be translational rather than transcriptional.