Identification and mechanistic analysis of shoot-to-root mobile mRNAs in a Nicotiana benthamiana/tomato heterografting system

In this study, we developed new heterografting systems, i.e., Nicotiana benthamiana/tomato, to study the shoot-to-root mRNA movement. The relatively distant phylogenetic relationships among the species involved in our heterografting system allowed easier distinguishment of scion mRNAs from the rootstock; in addition, the easiness of transformation for these species is another advantage if the molecular and physiological functional characterization of the identified mRNAs is a future research pursuit. Furthermore, we used this system to experimentally test: 1) whether the abundance of mRNAs in leaf is a deciding factor for the mobility of mRNAs; 2) whether the movement of mRNAs is under selection; 3) whether mobile mRNAs undergo degradation during their movement from shoot to root; 4) whether a shoot-to-root-shoot cycling process exists. In addition to the N. benthamiana/tomato heterografting system, we also developed another heterografting system in which canola is the scion and Arabidopsis is the rootstock. Our trial experiment showed that this is a valid system to identify shoot-to-root mobile mRNAs although more improvement is needed for this system.