Cucumber Mosaic Virus as a carotenoid inhibitor reducing Phelipanche aegyptiaca infection in tobacco plants.

Cucumber Mosaic Virus (CMV) is a highly infectious cucumovirus, which infects more than 800 plant species and causes major diseases in greenhouse and field crops worldwide. Parasitic weeds such as Phelipanche aegyptiaca are a major constraint to the production of many crops in the world and the parasite's lifestyle makes control extremely difficult. The parasite seeds can germinate after conditioning and perceiving strigolactones secreted by the host roots. Strigolactones are rhizosphere signaling molecules in plants that are biosynthesized through carotenoid cleavage. In the present study we investigated the possibility of reducing ß-carotene and then strigolactone production in the host roots by blocking carotenoid biosynthesis using CMV-infected tobacco. It was found that CMV downregulated the enzyme phytoene desaturase(PDS) and reduced significantly both carotenoid production and Phelipanche infection in tobacco host roots infected with both CMV and P. aegyptiaca. Based on our results (decrease of ß-carotene and repression of PDS transcripts in tobacco roots), we hypothesized that the reduction of Phelipanche tubercles and shoots occurred due to an effect of CMV on secondary metabolite stimulators such as strigolacetones. Our study indicated that mass production of the host roots was not affected by CMV; however, most inflorescences of Phelipanche grown on CMV-infected tobacco developed abnormally (deformed shoots and short nodes). Carotenoid biosynthesis inhibitors such as CMV can be used to reduce the production of strigolactones, which will lead to decreased Phelipanche attachment. Interestingly, attenuated CMV strains may provide a safe means for enhancing crop resistance against parasitic weeds in a future plan.

Movement of protein and macromolecules between host plants and the parasitic weed Phelipanche aegyptiaca Pers.

Little is known about the translocation of proteins and other macromolecules from a host plant to the parasitic weed Phelipanche spp. Long-distance movement of proteins between host and parasite was explored using transgenic tomato plants expressing green fluorescent protein (GFP) in their companion cells. We further used fluorescent probes of differing molecular weights to trace vascular continuity between the host plant and the parasite. Accumulation of GFP was observed in the central vascular bundle of leaves and in the root phloem of transgenic tomato plants expressing GFP under the regulation of AtSUC2 promoter. When transgenic tomato plants expressing GFP were parasitized with P. aegyptiaca, extensive GFP was translocated from the host phloem to the parasite phloem and accumulated in both Phelipanche tubercles and shoots. No movement of GFP to the parasite was observed when tobacco plants expressing GFP targeted to the ER were parasitized with P. aegyptiaca. Experiments using fluorescent probes of differing molecular weights to trace vascular continuity between the host plant and the parasite demonstrated that Phelipanche absorbs dextrans up to 70 kDa in size from the host and that this movement can be bi-directional. In the present study, we prove for the first time delivery of proteins from host to the parasitic weed P. aegyptiaca via phloem connections, providing information for developing parasite resistance strategies.