Marie Curie Individual Fellowship (EIF) Grants, Unión Europea. 2006-2007. P.I.: Juan A. López-Ráez
The germination stimulants in the root exudates of Orobanche host crops play an important role in the interaction between host and parasitic weed. Although the germination stimulants only induce the germination of specific parasite’s seeds, these compounds are strikingly similar and are probably derived from the same biosynthetic pathway (Bouwmeester et al., 2003). Considering the importance of these compounds in the lifecycle of parasitic weeds, it is surprising that so far very little is known about their biosynthetic origin. Most authors have defined the strigolactone germination stimulants as sesquiterpenoids. Recently the group of Bouwmeester has demonstrated, using carotenoid biosynthesis inhibitors and maize carotenoid and ABA mutants, that the maize, cowpea and sorghum germination stimulants are derived from the carotenoids (Matusova et al. in preparation). Considering the similarity between the strigolactone compounds that have been identified in a range of other plant species, including tomato (Yoneyama et al., 2004) it is clear that in all these species the origin of the germination stimulants must be carotenoid.
The project wais focused on a better understanding of the biosynthetic pathways of germination stimulants -strigolactones- and gave insights into the possibilities to use this knowledge to breed for plant resistance against parasitic weeds. We studied the regulation and effect of genes encoding enzymes involved in the biosynthetic pathways of the germination stimulants produced by tomato. We characterised tomato carotenoid/ABA mutans and studied their capacity to biosynthesise germination stimulants, using germination bioassays. In addition, we used molecular techniques to isolate and characterise cDNAs encoding relevant pathway enzymes. These genes were used to generate transgenic 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.