The role of strigolactones in host specificity ofOrobancheandPhelipancheseed germination

Abstract

Strigolactones are apocarotenoids regulating shoot branching. They are also known to be exuded by plant roots at very low concentrations, stimulating hyphal branching of arbuscular mycorrhizal fungi and germination of root parasitic weed seeds. We show that strigolactones play a major role in host specificity ofOrobancheandPhelipanche(the broomrapes) seed germination. This observation confirms that host-derived germination stimulants are an important component determining the host specificity of these parasitic plants. Weedy broomrape species were less specialized in germination requirements than the non-weedy species except forO. cumanaandO. foetidavar.broteri. Similar results were obtained with the root exudates. Some species, such asP. aegyptiacaandO. minor, showed a broad spectrum of host specificity in terms of seed germination, which was stimulated by exudates from the majority of species tested, whereas others, such asO. cumana,O. hederaeandO. densiflora, were highly specific. Some species, such asO. minor,P. aegyptiacaandP. nana, were responsive to the three strigolactones studied, whereas others were induced by only one of them, or did not respond to them at all. The synthetic strigolactone analogue GR24, generally used as a standard for germination tests, was not effective on someOrobancheandPhelipanchespecies. Seeds of some species that did not respond to GR24 were induced to germinate in the presence of fabacyl acetate or strigol, confirming the role of strigolactones in host specificity.

Response of wild and weedy broomrapes to synthetic strigolactone analogue GR24

“…2B). The similar effect was found for Orobanche crinita and Orobanche densiflora (Fernández-Aparicio, et al, 2011), S. asiatica, S. hermonthica, S. aspera and O. crenata . The high concentration of germination stimulant does not necessarily induce maximal germination of seeds and the non-optimal high concentration of GR24 might inhibit germination of parasitic weed seeds.…”

“…The single broomrapes might require unique combination and concentrations of signaling chemicals (Fernández-Aparicio, et al, 2011;Höniges, et al, 2012). In wild ecosystem there are growing many different plants (potential hosts) in the same area, colonized by arbuscular mycorrhizal fungi.…”

New Potent Fluorescent Analogues of Strigolactones: Synthesis and Biological Activity in Parasitic Weed Germination and Fungal Branching

“…and so were regarded as detrimental to the producing plants. [6][7][8] Subsequently, their role as indispensable chemical signals for the establishment of arbuscular mycorrhizas (AM), the widespread symbiosis between most land plants and a small group of soil fungi, was unveiled. [9][10][11][12][13] In addition to these functions in the rizosphere, it has recently been shown that SLs represent a new class of plant hormones that inhibit shoot branching.…”

The synthetic strigolactone GR24 influences the growth pattern of phytopathogenic fungi

“…Strigolactones (SLs) are known as plant hormones that are also released to the rhizosphere and interact with both mycorrhizal fungi and parasitic plant seeds (Bouwmeester et al 2003;Akiyama et al 2005;Xie et al 2010;Fernández-Aparicio et al 2011). Several authors have described growth stimulation of germinating arbuscular mycorrhizal (AM) fungi in the presence of unidentified host-root exudates, whereas exudates from non-mycotrophic species had no effect on these fungi (Graham 1982;Elias and Safir 1987;Gianinazzi-Pearson et al 1989;Bécard and Piché 1990;Giovannetti et al 1993Giovannetti et al , 1994Tawaraya et al 1996;Giovannetti and Sbrana 1998;Hirsch and Kapulnik 1998).…”