Strigolactone-Induced Putative Secreted Protein 1 Is Required for the Establishment of Symbiosis by the Arbuscular Mycorrhizal Fungus Rhizophagus irregularis

Abstract

Arbuscular mycorrhizal (AM) symbiosis is the most widespread association between plants and fungi. To provide novel insights into the molecular mechanisms of AM symbiosis, we screened and investigated genes of the AM fungus Rhizophagus irregularis that contribute to the infection of host plants. R. irregularis genes involved in the infection were explored by RNA-sequencing (RNA-seq) analysis. One of the identified genes was then characterized by a reverse genetic approach using host-induced gene silencing (HIGS), which causes RNA interference in the fungus via the host plant. The RNA-seq analysis revealed that 19 genes are up-regulated by both treatment with strigolactone (SL) (a plant symbiotic signal) and symbiosis. Eleven of the 19 genes were predicted to encode secreted proteins and, of these, SL-induced putative secreted protein 1 (SIS1) showed the largest induction under both conditions. In hairy roots of Medicago truncatula, SIS1 expression is knocked down by HIGS, resulting in significant suppression of colonization and formation of stunted arbuscules. These results suggest that SIS1 is a putative secreted protein that is induced in a wide spatiotemporal range including both the presymbiotic and symbiotic stages and that SIS1 positively regulates colonization of host plants by R. irregularis.

Evidence of non-tandemly repeated rDNAs and their intragenomic heterogeneity in Rhizophagus irregularis

“…1b, f, Supplementary Data 6). AMF has developed a unique signal pathway for symbiosis (e.g., establishments of symbiosis with pathways via SIS1 41 and lyso-phosphatidylcholine 42 ). This inflation of signaling-related genes may have led the development of a complex signaling pathway in AMF.…”

Comparative genomics and transcriptomics depict ericoid mycorrhizal fungi as versatile saprotrophs and plant mutualists

“…The symbiosis‐upregulated genes of ERM fungi include a cluster of taxonomically restricted genes specific to each ERM fungal species that contain a high proportion of effector‐like MiSSPs. Characterized MiSSPs dampen plant defense reactions in AM and ECM symbioses (Kloppholz et al ., ; Plett & Martin, ; Tsuzuki et al ., ). The percentage of MiSSPs (10–20% of total SSPs) in ERM falls in a range similar to that found for ECM fungi (4–21%; Kohler et al ., ) and for the AM fungus R. irregularis (19%, Tisserant et al ., ).…”

Comparative Analysis of Secretomes from Ectomycorrhizal Fungi with an Emphasis on Small-Secreted Proteins

“…Some SSPs with a similar activity were also described by functional analyses in mutualistic plant–fungal association (Kloppholz et al, 2011; Plett et al, 2011; Tsuzuki et al, 2016). More recently, a comparative in silico analysis revealed that many SSPs were shared by both arbuscular mycorrhizal fungi Rhizophagus clarus and Rhizophagus irregularis , supporting the role of secreted peptides in mycorrhizal associations (Sędzielewska Toro and Brachmann, 2016).…”