The negative regulator SMAX1 controls mycorrhizal symbiosis and strigolactone biosynthesis in rice

We present the identification of a negative regulator from rice, which operates downstream of the D14L receptor, corresponding to the homologue of the Arabidopsis thaliana Suppressor of MAX2-1 that functions in karrikin signalling

Jeongmin Choi; Tak Lee; Jungnam Cho; Emily K. Servante; Boas Pucker; William Summers; Sarah Bowden; Mehran Rahimi; Kyungsook An; Gynheung An; Harro J. Bouwmeester; Emma J. Wallington; Giles Oldroyd; Uta. Paszkowski


Scholarcy highlights

  • Most plants associate with beneficial arbuscular mycorrhizal fungi that facilitate soil nutrient acquisition
  • The SMXL family was divided into four subclades, corresponding to three known biological roles in karrikin signalling, phloem development, and in SLsignalling
  • Rice SMAX1 consists of three exons, encoding a protein of 1040 amino acids
  • There are three predicted domains with a nuclear localisation signal at the N-terminus, aligning to the functionally characterised NLS from homologous AtSMXL732, and a doubleClpN domain involved in protein interaction of chaperons and two P-loop ATPases
  • We demonstrate that the AM symbiosis depends on double negative regulatory mechanisms that link hormonal and pre-symbiotic signalling
  • As expected d14l and d3 single mutants displayed strong symbiosis defects with below 5% total fungal colonisation; d14l/smax and d3/smax double homozygous mutants had restored fungal colonisation with 84.8% and 79.6%, respectively
  • We identified rice SMAX1 as a suppressor of AM symbiosis development, functioning downstream of the D14L/D3 receptor complex since the SMAX1 mutation fully restored AM fungal colonisation in the d14l and d3 mutant backgrounds
  • BEE 1 DIP1b CBF1/2 CYCLOPS* AP2 Nodulation Signalling Pathway2* AP2 AP2 B-box zinc finger C3HC4 zinc finger B3 auxin response factor 75 Myb-like bHelix-loop-helix propose that an endogenous signal conditions the root for presymbiotic recognition of arbuscular mycorrhizal fungi via activation of the D14Lsignalling pathway leading to elimination of SMAX1 suppression

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