Parasitic weeds are among the most damaging agricultural pests. The Orobanche spp. (broomrapes) are holoparasites and parasitise important agricultural crops such as tomato, legumes, cruciferes, sunflower, hemp and tobacco in large parts of Europe, North A merica, Middle East, and India. These parasitic plants can grow rapidly and cause tremendous agricultural losses. Although the different genera of parasitic plants parasitise a whole range of different hosts in different parts of the world, their lifecycle s are broadly similar. One of the most important features in the host-parasitic plant interaction is signalling which occurs in many steps of this lifecycle. The first of these signals is the secretion of secondary metabolites from the roots of hosts that induce the germination of the seeds of the parasites. Although different parasitic plants parasitise different hosts in different parts of the world, their germination stimulants all belong to one class of compounds, the strigolactones such as strigol, ale ctrol and orobanchol. Recent work in the host group has shown that these germination stimulants are derived from the carotenoid/ABA pathway. In this project we will study the genes encoding enzymes involved in the biosynthetic pathways of the germinatio n stimulants produced by tomato. Hereto, we will characterise tomato carotenoid/ABA mutans and study their capacity to biosynthesise germination stimulants using germination bioassays. To find genes involved in the so far unknown part of the pathway, we wi ll screen a mutant population of tomato for mutants disturbed in the induction of germination. In addition, we will use molecular techniques to isolate and characterise cDNAs encoding relevant pathway enzymes. These genes will be used to generate transgeni c tomato plants, by both antisense and sense constructs, with altered expression of these genes to evaluate and compare with wild type plants for their susceptibility for O. ramosa and O. aegyptiaca.
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