The Role Of DELLAs-MtDIP1-RAM1 Protein Complex In Arbuscular Mycorrhizal Symbiosis

80%-90% terrestrial plants, including most crop rice(Oryza sativa), wheat(Triticum spp.), maize(Zea mays) and soybean(Glycine-max), are able to form symbiotic associations with arbuscular mycorrhizal fungi(AMF). The arbuscular mycorrhizal association that helps the host plant to uptake nutrients from the soil and is especially important for plant acquisition of phosphate and nitrogen, in turn the host plant provides carbonhydrate to the AM fungi.The early chemical communication between the host plant root and arbuscular mycorrhizal fungi(AMF) in the rhizosphere is essential for the iniation of symbiosis. Plant root releases signal molecules to rhizosphere such as Strigolactones which is perceived by AM fungi in soil and induces germination of AM fungal spores, hyphae branching and secretion of mycorrhizal factors(Myc factors). Myc factors are recognized by the plasma membrane receptor and active the calcium spiking in the nucleus of the cell. The calcium signal can be decoded by the calcium and calmodulin dependent kinase CCaMK/DMI3, which cause CCaMK/DMI3 autophosphorylation and phosphorylates IPD3 which is substrate of CCaMK. The mechanisms of symbiotic signaling between plant and AM fungi are still complicated and there are many questions need to be answered, Such as: What is the receptor of myc factors and how it actives the signaling pathway; What is mechanism underling the transcription factors active the expression of AM related genes and so on. Here we show the mechanism of transcription factors regulating the expression of AM genes during mycorrhizal symbiosis.In our study, we analysed the role of MtDIP1 in the AM symbiosis signaling pathway using two Tnt1 insertion mutants of GRAS transcription factor MtDIP1. Our results show that expression of MtDIP1 is up-regulated during mycorrhizal infection. The transcriptional level of DIP1 in dip1 mutants is great reduced and AM fungal colonization is also much lower than wild type. Expression of mycorrhizal marker genes Mt Lec5, MtGlp1, MtHA1, Mt PT4 and MtNR are not fully induced in dip1-1 mutant compared with wild type, indicating the function of MtDIP1 in AM symbioitic pathway. Using yeast two hybrid and pull down assay, we show that MtDIP1 physical interacts with MtDELLAs and MtRAM1 respectively, which both are required for mycorrhizal symbiosis. A transient reporter assay shows that MtDIP1 combined with DELLA and RAM1 actives the expression of AM symbiosis gene. We conclude that DELLA-MtDIP1-RAM1 may form protein complex regulates AM symbiosis through directly activating expression of AM symbioitic genes during mycorrhizal symbiosis.