Strigolactones, ROS and ABA Regulate Systemic Salt-Tolerance Priming Signals Between Dodder-Connected Tobacco Plants

The parasitic plants dodders (Cuscuta spp., Convolvulaceae) can often simultaneously parasitize two or more neighbouring hosts, forming dodder-connected plant clusters. In a dodder-connected plant cluster, salt-induced systemic priming signals are transferred from the salt-stressed host (signal donor, SD) to the other host (signal receiver, SR) through dodder and prime the SR plants for enhanced salt tolerance, but what signalling pathways regulate the dodder-mediated interplant priming signals remain unclear. In this study, using genetic analyses, we show that in dodder-connected tobacco (Nicotiana tabacum) clusters, the strigolactone (SL), reactive oxygen species (ROS) and abscisic acid (ABA) pathway in the SD plants negatively control the salt stress-induced systemic signals from SD to SR plants. Transcriptome data suggested that the salt-induced systemic signals regulated by SLs in the SD plants may also affect the ABA and ROS signalling pathway in the SR plants. Quantification of the ABA and H₂O₂ contents in the SD plants suggested that the SL and ROS signalling likely converge on the ABA pathway to regulate the priming signals. This study reveals the important regulatory roles of phytohormones and ROS in dodder-mediated interplant communications and provides new insight into systemic signalling during salt stress adaptation in individual plants.