Strigolactones promote nodulation in pea

Abstract

Strigolactones are recently defined plant hormones with roles in mycorrhizal symbiosis and shoot and root architecture. Their potential role in controlling nodulation, the related symbiosis between legumes and Rhizobium bacteria, was explored using the strigolactone-deficient rms1 mutant in pea (Pisum sativum L.). This work indicates that endogenous strigolactones are positive regulators of nodulation in pea, required for optimal nodule number but not for nodule formation per se. rms1 mutant root exudates and root tissue are almost completely deficient in strigolactones, and rms1 mutant plants have approximately 40% fewer nodules than wild-type plants. Treatment with the synthetic strigolactone GR24 elevated nodule number in wild-type pea plants and also elevated nodule number in rms1 mutant plants to a level similar to that seen in untreated wild-type plants. Grafting studies revealed that nodule number and strigolactone levels in root tissue of rms1 roots were unaffected by grafting to wild-type scions indicating that strigolactones in the root, but not shoot-derived factors, regulate nodule number and provide the first direct evidence that the shoot does not make a major contribution to root strigolactone levels.

Strigolactones fine-tune the root system

“…2) (Soto et al 2010), supporting the role of strigolactones in regulating organ development. In agreement, the pea mutant rms1 was shown to carry less nodules per gram weight compared to control plants and this effect was complemented by exogenous GR24 (Foo and Davies 2011). These data are in agreement with a positive role of endogenous strigolactones in nodulation.…”

Strigolactone Involvement in Root Development, Response to Abiotic Stress, and Interactions with the Biotic Soil Environment

“…The potential of strigolactones to control nodulation was verified using the strigolactone-deficient rms1 mutant in pea (Foo and Davies, 2011). This work showed that endogenous strigolactones are positive regulators of nodulation in this plant.…”

“…Application of GR24 to rms1 plants resulted in an increase in the number of nodules on the mutant roots to the level obtained on the wild type (without exogenous application of strigolactones). GR24 application can also enhance nodule number in wild-type pea, alfalfa, and Lotus japonicus (Soto et al, 2010;Foo and Davies, 2011;Liu et al, 2013). It was also shown that strigolactones in the root but not shoot-derived factors can regulate nodule number (Foo et al, 2014).…”

“…It was only later that strigolactones were also identified as stimulants of hyphal branching in AMF (Akiyama et al, 2005;Besserer et al, 2006Besserer et al, , 2008Gomez-Roldan et al, 2008;Yoneyama et al, 2008). In addition, strigolactones were shown to stimulate nodulation (Nod) in the legume-rhizobium interaction process (Soto et al, 2010;Foo and Davies, 2011).…”

“…This work showed that endogenous strigolactones are positive regulators of nodulation in this plant. Using rms1 mutant root exudates and root tissue that were almost completely deficient in strigolactones, Foo and Davies (2011) showed a 40% reduction in the number of nodules relative to wild-type plants that contained strigolactones. Application of GR24 to rms1 plants resulted in an increase in the number of nodules on the mutant roots to the level obtained on the wild type (without exogenous application of strigolactones).…”