Mechanistic Insights Into The Arbuscular Mycorrhizal Fungi On The Growth Of Switchgrass During Seedling Stage And Molecular Mechanisms Of Small G Protein NFIP1 In The Noule Symbiosis Of Medicago Truncatula

Symbiosis is an important strategy for plants to adapt the environment,a lot of plants can form a mutually beneficial symbiotic relationship with many kinds of microorganisms.These microbes can get the nutrients from soil or air and transport to the plant,at the same time,plant photosynthesis can produce carbon souece to meet the grow of microorganisms.Currently symbiotic relationship most studied is the the symbiosis between most of land plants and arbuscular mycorrhizal fungi.Another kind is nitrogen-fixing symbiosis betweenleguminous plants and rhizobia.Switchgrass(Panicum virgatum L.)is a perennial C4 grass of Gramineae Panicum,and mycorrhizal symbiosis can significantly improve the yield of switchgrass.Switchgrass grows slowly during seedling stage,while we know little about whether mycorrhizal symbiosis also has positive effects on the growth at this stage.Ma and Mg,were inoculated by Arbuscular mycorrhizal fungi(AMF).It has been reported that plant specific small G protein involved in nodule symbiosis,but we know little about whether NFIP1 is involved in nodules,and its role in signal transduction of symbiotic nitrogen fixation mechanism remains unclear.The main results are as follows:1.The roots of switchgrass was successfully infected by AMF and formed arbuscular mycorrhizae.AMF treatment increased the content of chlorophyll,and improved the growth of roots,leaves and biomass.2.The induction ability of root extracts on Orobanche aegyptiaca seeds germination was dramatically declined after inoculated by AMF.In addition,the expression of mark genes of Strigolactones D10 and D27 were decreased markly in Mg with AMF.Our results suggested that switchgrass inoculated with AMF at seedling stage may biosynthesis and secrete lessstrigolactones,a newly identified plant hormone with inhibitory effects on plant branching,which further promote the growth of switchgrass at seedling stage.3.Yeast two hybrid system and Pull down assay indicated that medicago truncatula small G protein NFIP1 interacted with nodular factor receptor mainly in the activity form.The nodule number per plant reduced after gene silence of NFIP1,LORE1 mutant of orthologous genes LjNFIP1 in lotus infection threads,primordial number and nodule number were decreased significantly reduced,indicating that NFIP1 positivly regulate the nodule symbosis.4.The nodule number was reduced after gene silencingof Guanine nucleotide exchang factor LYIP2 indicating that NFIP1 positivly regulate the nodule symbosis.Yeast two hybrid system and Pull down assay indicated that LYIP2 could respectively interact with NFIP1 and nodule factor receptor LYK3.In vitro phosphorylation experiments showed that LYIP2 was phosphorylated by LYK3.Overexpression of LYIP2 restored the phenotype of LYK3 mutant hcl-1 which the growth of root hair was inhabited,NFIP1 only partially restored the phenotype.Compared with the control,they both had more white bumps similar to nodule.This suggested that LYIP2 in nodular factor receptor LYK3 downstream,activated by LYK3 phosphorylation and control the activity of NFIP1.5.The analysis of promoters drive GUS reporter gene showed that NFIP1 and LYIP2 had strong expression in immature and mature nodules,further indicated that NFIP1 and LYIP2 participated in the nodule symbiosis.