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Summary: In terrestrial ecosystems, most plant species can form beneficial associations with arbuscular mycorrhizal (AM) fungi. Arbuscular mycorrhizal fungi benefit plant nutrient acquisition and enhance plant tolerance to drought. The high osmolarity glycerol 1 mitogen‐activated protein kinase (HOG1‐MAPK) cascade genes have been characterized in Rhizophagus irregularis. However, the upstream receptor of the HOG1‐MAPK cascade remains to be investigated.We identify the receptor kinase RiSho1 from R. irregularis, containing four transmembrane domains and one Src homology 3 (SH3) domain, corresponding to the homologue of Saccharomyces cerevisiae. Higher expression levels of RiSho1 were detected during the in planta phase in response to drought. RiSho1 protein was localized in the plasma membrane of yeast, and interacted with the HOG1‐MAPK module RiPbs2 directly by protein–protein interaction.RiSho1 complemented the growth defect of the yeast mutant ∆sho1 under sorbitol conditions. Knock‐down of RiSho1 led to the decreased expression of downstream HOG1‐MAPK cascade (RiSte11, RiPbs2, RiHog1) and drought‐resistant genes (RiAQPs, RiTPSs, RiNTH1 and Ri14‐3‐3), hampered arbuscule development and decreased plants antioxidation ability under drought stress.Our study reveals the role of RiSho1 in regulating arbuscule development and drought‐resistant genes via the HOG1‐MAPK cascade. These findings provide new perspectives on the mechanisms by which AM fungi respond to drought. [ABSTRACT FROM AUTHOR]

Nodulation and arbuscular mycorrhization require the activation of plant host symbiotic programs by Nod factors, and Myc- LCOs and COs, respectively. The pathways involved in the perception and downstream signaling of these signals include common and distinct components. Among the distinct components, NSP1, a GRAS transcription factor, has been considered for years to be specifically involved in nodulation., Here, we analyzed the degree of conservation of the NSP1 sequence in arbuscular mycorrhizal ( AM) host and non- AM host plants and carefully examined the ability of Medicago truncatula nsp1 mutants to respond to Myc- LCOs and to be colonized by an arbuscular mycorrhizal fungus., In AM-host plants, the selection pressure on NSP1 is stronger than in non- AM host ones. The response to Myc- LCOs and the frequency of mycorrhizal colonization are significantly reduced in the nsp1 mutants., Our results reveal that NSP1, previously described for its involvement in the Nod factor signaling pathway, is also involved in the Myc- LCO signaling pathway. They bring additional evidence on the evolutionary relatedness between nodulation and mycorrhization. [ABSTRACT FROM AUTHOR]