From lateral root density to nodule number, the strigolactone analogue GR24 shapes the root architecture of Medicago truncatula

Abstract

In the rhizosphere, strigolactones not only act as crucial signalling molecules in the communication of plants with parasitic weeds and arbuscular mycorrhiza, but they also play a key role in regulating different aspects of the root system. Here we investigated how strigolactones influence the root architecture of Medicago truncatula. We provide evidence that addition of the synthetic strigolactone analogue GR24 has an inhibitory effect on the lateral root density. Moreover, treatment with GR24 of Sinorhizobium meliloti-inoculated M. truncatula plants affects the nodule number both positively and negatively, depending on the concentration. Plants treated with 0.1 µM GR24 had a slightly increased number of nodules, whereas concentrations of 2 and 5 µM strongly reduced it. This effect was independent of the autoregulation of nodulation mechanism that is controlled by SUPER NUMERIC NODULE. Furthermore, we demonstrate that GR24 controls the nodule number through crosstalk with SICKLE-dependent ethylene signalling. Additionally, because the expression of the nodulation marker EARLY NODULATION11 was strongly reduced in GR24-treated plants, we concluded that strigolactones influence nodulation at a very early stage of the symbiotic interaction.

GmMAX2–D14 and –KAI interaction‐mediated SL and KAR signaling play essential roles in soybean root nodulation

“…SLs or KARs act as a rhizosphere signal to promote the plant-AMF symbioses by promoting spore germination and hyphal branching (Akiyama et al, 2005). Due to the common signaling mechanism shared by AMF-and rhizobia-legume symbiotic interactions (Oldroyd, 2013), SLs were also suggested to participate in nodulation in several legumes (Soto et al, 2010;Foo and Davies, 2011;Liu et al, 2013;Seto et al, 2014;De Cuyper et al, 2015;Haq et al, 2017;McAdam et al, 2017).…”

Strigolactones in the Rhizosphere: Friend or Foe?

“…In addition, the nodule number decreases significantly in rms5 mutants, which are defective in PsCCD7 (Foo et al 2013), but it increases in the strigolactone-insensitive rms4 mutant that is affected in the Arabidopsis ortholog MAX2 involved in strigolactone signaling (Foo and Davies 2011). Although this observation contrasts with the data obtained for the rms1 mutants and the LjCCD7 lines, rac-GR24 treatment could affect the nodule number in a concentration-dependent manner in Medicago truncatula (barrel medic), with a stimulating effect at low rac-GR24 concentrations and a negative effect at high concentrations (De Cuyper et al 2015).…”

“…Strigolactones are present in root exudates of diverse monocotyledonous and dicotyledonous plant species at very low concentrations (picomolar and nanomolar) (Xie 2016). In the soil, these molecules are implicated in the communication between plants and a wide range of parasites belonging to the Orobanchaceae family (Cook et al 1966;Yoneyama et al 2010) but, also, in the communication with arbuscular mycorrhizal fungi (Akiyama et al 2005) and, more recently, in the legume-rhizobia symbiosis (De Cuyper et al 2015;Foo and Davies 2011;Peláez-Vico et al 2016;Soto et al 2010). In addition to their importance as rhizosphere molecules, strigolactones are also studied for their role as plant hormones that influence various physiological processes to adjust plant growth and development, such as shoot branching, secondary growth processes, leaf shape and senescence, internode elongation, and environmental stress responses (Al-Babili and Bouwmeester 2015).…”

Phytohormonal regulation of legume-rhizobium symbiosis

“…Обробка M. truncatula і P. sativum синтетичним аналогом стриголактонів GR24 у низьких концентраціях індукує невелике збільшення кількості кореневих бульбочок [82][83][84], що вказує на позитивну регуляцію стриголактонами бульбочкоутворення в низці рослин. Проте у високій концентрації GR24 пригнічує нодуляцію [84]. Це свідчить, що вплив стриголактонів, як і інших фітогормонів, на нодуляцію залежить від оптимального діапазону їх концентрації [38].…”