Strigolactones and the Regulation of Pea Symbioses in Response to Nitrate and Phosphate Deficiency

Abstract

New roles for the recently identified group of plant hormones, the strigolactones, are currently under active investigation. One of their key roles is to regulate plant symbioses. These compounds act as a rhizosphere signal in arbuscular mycorrhizal symbioses and as a positive regulator of nodulation in legumes. The phosphorous and nitrogen status of the soil has emerged as a powerful regulator of strigolactone production. However, until now, the potential role of strigolactones in regulating mycorrhizal development and nodulation in response to nutrient deficiency has not been proven. In this paper, the role of strigolactone synthesis and response in regulating these symbioses is examined in pea (Pisum sativum L.). Pea is well suited to this study, since there is a range of well-characterized strigolactone biosynthesis and response mutants that is unique amongst legumes. Evidence is provided for a novel endogenous role for strigolactone response within the root during mycorrhizal development, in addition to the action of strigolactones on the fungal partner. The strigolactone response pathway that regulates mycorrhizal development also appears to differ somewhat from the response pathway that regulates nodulation. Finally, studies with strigolactone-deficient pea mutants indicate that, despite strong regulation of strigolactone production by both nitrogen and phosphate, strigolactones are not required to regulate these symbioses in response to nutrient deficiency.

Strigolactones fine-tune the root system

“…These data are in agreement with a positive role of endogenous strigolactones in nodulation. Interestingly, rms4 mutants affected in strigolactone response carried more nodules than the wild type, which is the opposite phenotype to rms1 (Foo et al 2013). This discrepancy demonstrates that there is still much to be discovered about strigolactone signaling and it supports the hypothesis that the F-box protein is involved in signaling processes other than just RMS1-produced strigolactones .…”

Phosphate Treatment Strongly Inhibits New Arbuscule Development But Not the Maintenance of Arbuscule in Mycorrhizal Rice Roots

“…Transcriptome analyses of mycorrhizal petunia roots under varying P conditions demonstrated the absence of defense responses and significant down-regulation of genes encoding enzymes of carotenoid and strigolactone biosynthesis (Breuillin et al, 2010). Biosynthesis, transport, and signaling events of strigolactone-related molecules are required for normal colonization (Floss et al, 2008;Vogel et al, 2010;Kretzschmar et al, 2012;Yoshida et al, 2012;Foo et al, 2013;Gutjahr et al, 2015). Strigolactones also induce hyphal branching (Akiyama et al, 2005) and increase the production of symbiotic fungal signals (Genre et al, 2013).…”

From little things big things grow: karrikins and new directions in plant development

“…Although strigolactone production is thus important for successful AM colonisation, it is not necessary, because strigolactone biosynthesis mutants nevertheless develop functional symbioses (Gomez-Roldan et al 2008;Kohlen et al 2012;Kretzschmar et al 2012). Somewhat confusingly, the F-box protein D3/RMS4/MAX2 was shown to be essential for AM symbioses in both rice (Yoshida et al 2012) and pea (Foo et al 2013). However, it became clear that D14 was not responsible for regulating this aspect of MAX2 function, because rice d14 mutants did not show the same AMdeficient phenotype as d3 (Yoshida et al 2012).…”