Abstract Genera of the Orobanchaceae family are holoparasites that parasitize various hosts. Several members of this family cause severe damage to diverse crop plants. While the biological and life cycles of these parasites have been studied, their metabolism has received little attention, most of which focused on Phelipanche aegyptiaca . This study aimed at obtaining more knowledge about the primary metabolic profiling of four parasite species belonging to the Orobanchaceae family – Orobanche cumana , Orobanche cernua , Phelipanche aegyptiaca and Phelipanche ramosa – that developed on tomato ( Solanum lycopersicum L.) as a host. Using GC-MS, it was shown that significant differences in metabolites content occur between species belonging to Orobanche compared to those belonging to Phelipanche . This finding adds another layer to the separation of these two genera in addition to morphological separation. Moreover, each of these four species exhibits different metabolic profiles, indicating that the parasites can absorb the host’s metabolites but also have the ability to self-regulate their metabolites in order to grow and develop.
Orobanche and Phelipanche, commonly known as broomrape, are dicotyledonous holoparasitic flowering plants that cause heavy economic losses in a wide variety of plant species. Egyptian broomrape (Phelipanche aegyptiaca Pomel.) parasitizes more than 30 food and ornamental crops, including tomato, sunflower, tobacco, chickpea and many others in different parts of the world. Crenate broomrape (Orobanche crenata Forsk.) parasitizes important legume crops, such as lentil, faba bean, chickpea, pea, vetches, and grass pea, as well as some apiaceous crops, such as carrot (4). This is the first report of pomegranate (Punica granatum L.) as a new host for broomrape. This is also the first report of broomrape parasitism on a Lythraceae family member. Because of their high value for human health, the demand for pomegranate fruits has increased tremendously in the last few years and the extent of pomegranate growth has increased significantly in many regions throughout the world. In March 2013, heavy broomrape infection of a 10-year-old pomegranate orchard near the village Kfar Pines was reported. The infected area of about 2 ha was located in the middle of a big pomegranate orchard (variety 116). Broomrape inflorescence counts in the infected area revealed 14 and 0.6 P. aegyptiaca and O. crenata shoots per m 2 , respectively. Both broomrape species were uniformly distributed over all the infected area. No differences of infection rate between the pomegranate trees could be observed. The inflorescences of the two species were normal and healthy and produced germinable seeds. Digging up the inflorescences verified a direct connection between the parasites and the pomegranate roots. The parasite species were identified morphologically according to Flora Europea (2) and Flora Palaestina (3). Detailed description of the two parasites may be found in (4). Identification was confirmed using unique DNA marker based on the photosynthetic gene rbcL of O. crenata. rbcL primers were able to distinguish between the above two species according to differences in PCR products yielding 390 bp for P. aegyptiaca and 300 bp for O. crenata (1). This was the first time that broomrapes had appeared in the orchard since its establishment, on fields that had been intensively used for processing tomato. No legume cropping history in the infected areas is known. It may be hypothesized that the broomrape seeds were dormant in the soil for over 10 years (4).The extremely wet and hot weather conditions of winter 2012/13 induced their germination. A total of 730 mm of rainfall was measured for that year as compared to the annual average of 560 mm for the region. High-level infestations with P. aegyptiaca and O. crenata were also reported from two other pomegranate orchards, Givat Ada and Evron, 11 km west and 81 km north of Kfar Pines, respectively. Neither symptoms nor visible qualitative or quantitative damage could be observed on the infected vs. non-infected pomegranate trees. However, pomegranate appears to be an alternate host for P. aegyptiaca and O. crenata serving as a seed inoculum source for nearby sensitive field crops. References: (1) R. Aly et al. Joint Workshop of the EWRS Working Groups, 29 September – 3 October, Chania, Crete, Greece, 2013. (2) A. O. Chater and D. A. Webb. Orobanche. Page 285 in: Flora Europaea, Vol. 3. T. G. Tutin et al., eds. University Press, Cambridge, 1972. (3) N. Feinbrun-Dothan. Page 210 in: Flora Palaestina, Vol. 3. Israel Academy of Sciences and Humanities, Jerusalem, 1978. (4) D. M. Joel et al., eds. Parasitic Orobanchaceae: Parasitic Mechanisms and Control Strategies. Springer Verlag Berlin Heidelberg, 2013.
Chickpea (Cicer arietinum L.) is a major pulse crop in Israel grown on about 3000 ha spread, from the Upper Galilee in the north to the North-Negev desert in the south. In the last few years, there has been a gradual increase in broomrape infestation in chickpea fields in all regions of Israel. Resistant chickpea cultivars would be simple and effective solution to control broomrape. Thus, to develop resistant cultivars we screened an ethyl methanesulfonate (EMS) mutant population of F01 variety (Kabuli type) for broomrape resistance. One of the mutant lines (CCD7M14) was found to be highly resistant to both Phelipanche aegyptiaca and Orobanche crenata. The resistance mechanism is based on the inability of the mutant to produce strigolactones (SLs)-stimulants of broomrape seed germination. LC/MS/MS analysis revealed the SLs orobanchol, orobanchyl acetate, and didehydroorobanchol in root exudates of the wild type, but no SLs could be detected in the root exudates of CCD7M14. Sequence analyses revealed a point mutation (G-to-A transition at nucleotide position 210) in the Carotenoid Cleavage Dioxygenase 7 (CCD7) gene that is responsible for the production of key enzymes in the biosynthesis of SLs. This nonsense mutation resulted in a CCD7 stop codon at position 70 of the protein. The influences of the CCD7M14 mutation on chickpea phenotype and chlorophyll, carotenoid, and anthocyanin content were characterized.
Aromatic amino acids (AAAs) synthesized in plants via the shikimate pathway can serve as precursors for a wide range of secondary metabolites that are important for plant defense. The goals of the current study were to test the effect of increased AAAs on primary and secondary metabolic profiles and to reveal whether these plants are more tolerant to abiotic stresses (oxidative, drought and salt) and to Phelipanche egyptiaca (Egyptian broomrape), an obligate parasitic plant. To this end, tobacco ( Nicotiana tabacum ) plants were transformed with a bacterial gene (AroG) encode to feedback-insensitive 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase, the first enzyme of the shikimate pathway. Two sets of transgenic plants were obtained: the first had low expression of the AroG protein, a normal phenotype and minor metabolic changes; the second had high accumulation of the AroG protein with normal, or deleterious morphological changes having a dramatic shift in plant metabolism. Metabolic profiling analysis revealed that the leaves of the transgenic plants had increased levels of phenylalanine (up to 43-fold), tyrosine (up to 24-fold) and tryptophan (up to 10-fold) compared to control plants having an empty vector (EV) and wild type (WT) plants. The significant increase in phenylalanine was accompanied by higher levels of metabolites that belong to the phenylpropanoid pathway. AroG plants showed improved tolerance to salt stress but not to oxidative or drought stress. The most significant improved tolerance was to P. aegyptiaca . Unlike WT/EV plants that were heavily infected by the parasite, the transgenic AroG plants strongly inhibited P. aegyptiaca development, and only a few stems of the parasite appeared above the soil. This delayed development of P. aegyptiaca could be the result of higher accumulation of several phenylpropanoids in the transgenic AroG plants and in P. aegyptiaca , that apparently affected its growth. These findings indicate that high levels of AAAs and their related metabolites have the potential of controlling the development of parasitic plants.
