Apple phloem cells contain some mRNAs transported over long distances

Apple (Malus x domestica Borkh.), like many fruit trees, cannot be propagated clonally from seed and is instead propagated by the grafting onto rootstocks. Rootstocks affect the growth of scions, but it is not known why. The circulation of some mRNAs throughout the phloem has recently been shown. To clarify whether RNAs are transported long distance through the graft union of apple trees, we analyzed cDNAs derived from shoot phloem cells by laser capture microdissection. We detected several mRNAs that have already been reported as phloem-transported RNAs in other plants. One of them, MpSLR/IAA14, was probed to transport a long distance through the graft union in grafted apple plant. These results suggest that a phloem RNA transport system may be involved in the effects of rootstocks on scion growth and cropping.