Strigolactones as Germination Stimulants for Root Parasitic Plants

Abstract

Witchweeds (Striga spp.) and broomrapes (Orobanche and Phelipanche spp.) are the two most devastating root parasitic plants belonging to the family Orobanchaceae and are causing enormous crop losses throughout the world. Seeds of these root parasites will not germinate unless they are exposed to chemical stimuli, ‘germination stimulants’ produced by and released from plant roots. Most of the germination stimulants identified so far are strigolactones (SLs), which also function as host recognition signals for arbuscular mycorrhizal fungi and a novel class of plant hormones inhibiting shoot branching. In this review, we focus on SLs as germination stimulants for root parasitic plants. In addition, we discuss how quantitative and qualitative differences in SL exudation among sorghum cultivars influence their susceptibility to Striga.

Molecular mechanism of strigolactone perception by DWARF14

“…Although SLs also function in arbuscular mycorrhizal fungi hyphal branching and in seed germination of parasitic plants, structure-activity relationships are different among individual organisms 4,8,42 , suggesting that each organism uses a distinct SL recognition system. The identification of SL perception mechanisms in different organisms would provide further information.…”

“…In addition, SLs stimulate the germination of root parasitic weeds 3,4 that cause devastating crop damage 5 and induce hyphal branching in symbiotic arbuscular mycorrhizal fungi that promote the growth of host plants by capturing essential inorganic nutrients from the soil [6][7][8] . Owing to the importance of SLs in agriculture, the mechanism and signal transduction pathway of SLs have been extensively researched to provide a perspective on the broader SL functions.…”

“…When both ( ± )-GR24 and GA 4 were added, OsGID1-expressing yeast cells could not grow on the medium lacking L-histidine and adenine. This result indicates that the formation of the GR24-dependent D14-SLR1 complex is inhibited by the GA 4 -bound OsGID1, and the D14-interacting domain overlaps with the OsGID1-interacting domain in SLR1. When only ( ± )-GR24 was added to the growth medium, yeast colonies could grow independently of GID1 expression.…”

Striga

“…Striga seeds require a period of pre-treatment, conditioning in a moist warm environment (30°C in germination bioassays) for 2 to 16 days before they acquire potential to germinate (Longan and Stewart, 1991;Parker and Riches, 1993). After this phase, germination of Striga seeds will be initiated only upon induction by some specific chemicals, such as strigolactones, released by the host roots into the rhizosphere (Bouwmeester et al, 2003;Matusova et al, 2005;Shen et al, 2006;Yoneyama et al, 2010;Xie et al, 2010). The concentration of such chemicals is very low and ranges from 10 -10 to 10 -15 mole m -3 (Hearne, 2009).…”

“…The development of highly advanced analytical methods, for example the high performance liquid chromatography (HPLC) connected to tandem mass spectrometry (LC-MS/MS) (Sato et al, 2003), has allowed new SLs to be surveyed in the root exudates of many different plant species, including few millet species (Akiyama et al, 2005;Awad et al, 2006;Xie et al, 2007;Matsuura et al, 2008;Xie et al, 2008;Xie et al, 2009a;Xie et al, 2009b;Yoneyama et al, 2010;Kohlen et al, 2011;Ueno et al, 2011;Jamil et al, 2012). …”