Phosphorus deficiency in red clover promotes exudation of orobanchol, the signal for mycorrhizal symbionts and germination stimulant for root parasites

Abstract

Plant derived sesquiterpene strigolactones, which have previously been characterized as germination stimulants for root parasitic plants, have recently been identified as the branching factors which induce hyphal branching morphogenesis, a critical step in host recognition by arbuscular mycorrhizal (AM) fungi. We show here that, in red clover plants (Trifolium pratense L.), which is known as a host for both AM fungi and the root holoparasitic plant Orobanche minor Sm., reduced supply of phosphorus (P) but not of other elements examined (N, K, Mg, Ca) in the culture medium significantly promotes the release of a strigolactone, orobanchol, by the roots of this plant. In red clover plants, the level of orobanchol exudation appeared to be regulated by P availability and was in good agreement with germination stimulation activity of the root exudates. This implies that under P deficiency, plant roots attract not only symbiotic fungi but also root parasitic plants through the release of strigolactones. This is the first report demonstrating that nutrient availability influences both symbiotic and parasitic interactions in the rhizosphere.

Strigolactones fine-tune the root system

“…This is in agreement with measurements of Yoneyama et al (2007), in which higher levels of strigolactones were found in roots as compared to other tissues. Little is known about what controls the level of strigolactone synthesis, although light quality and intensity could be the determining factors (Koltai et al 2011).…”

“…In contrast to lateral root formation, Pi-deficient inhibition of root growth occurs independently of strigolactone signaling, as evidenced by Pi-deficient inhibition of primary root growth in both max2 and wild type (Yoneyama et al 2007;Jain et al 2007;Mayzlish-Gati et al 2012).…”

“…In contrast, under low levels of Pi, lateral root initiation and elongation are favored over primary root growth (Williamson et al 2001) while strigolactone production increases (Yoneyama et al 2007). Importantly, the action of strigolactones on lateral root formation/initiation depends on the Pi status of the plant.…”

Strigolactones as mediators of plant growth responses to environmental conditions

“…[55][56][57][58] Hence, it is possible that SLs provide a way for the plant to coordinate shoot development with nutritional conditions.…”

The role of strigolactones in root development

“…11,12 SLs play key roles in adaptive responses to N and P deficiencies due to elevated SL levels in roots. [13][14][15][16][17] For example, SLs promote symbioses with arbuscular mycorrhizal fungi by inducing hyphal branching and they adjust shoot architecture by inhibiting tiller bud outgrowth to better adapt to a P or N deficiency. 14,[16][17][18][19][20][21] Recently, it was reported that SLs regulate the perception or response of plants to P-limited conditions.…”