Effects Of Arbuscular Mycorrhizal Fungi On Salt Tolerance Of Suaeda Salsa In Molecular Mechanism

Salinization in soils has disturbed on agricultural production and the ecological stability in China and even all over the world.The area of salinized soil in Inner Mongolia is about 7.63 million hectares,which has many impacts on the sustainable development of agriculture and stockbreeding.Salinization in soils lead to a bad soil quality and contain lota of salt,which can inhibit the growth of plants.It is concerned that using halophytes to rehabilitate the salinized soil,because halophytes have high tolerance for salinity,and even certain halophytes can grow better under moderate salt conditions.Previous studies have shown that arbuscular mycorrhizal(AM)fungi can promote plants to adapt salt environments and relieve salt stress.However,it is rarely reported in the effects of AM fungi on salt tolerance of halophytes.Whether the effect of AM fungi on salt tolerance of halophytes is different from that of glycophytes;how to regulate the salt tolerance of halophytes by AM fungi at molecular levels;whether the greater potential for remediation of salinization soil can be exerted with halophytes combined with AM fungi.A pot experiment was carried out to investigate the effects of AM fungi on growth,ion balance,antioxidant enzymes,osmotic regulators,salt tolerance-related genes and rhizosphere bacterial community structure and composition in halophyte Suaeda salsa under 0 m M,100 m M,200 m M and 400 m M Na Cl.Next,the regulation of AM fungi in halophyte Suaeda salsa under 100 m M Na Cl was researched,using transcriptome and proteomics.The results showed that the symbiotic relationship between the AM fungi(Funneliformis mosseae)and the halophyte(S.salsa)was successfully established,and the colonization ranged from 20.4% to42.0% in mycorrhizal S.salsa.The modest salt concentration can promote the plants growth.AM fungi increased the dry weight of shoots and roots at 100 m M Na Cl,and promoted the growth of S.salsa.The K,Ca and Mg concentrations of shoots and K concentration of roots in salt conditions were decreased,compared with no-salt conditions.The plants in salt conditions decreased the K:Na ratio of shoots and roots by 95.3%-98.8%.Mycorrhizal plants had the higher Ca and Mg concentrations of shoots compared with the non-mycorrhizal plants under the same salt concentrations.For example,AM fungi increased the Ca and Mg concentrations by 50.0% and 47.6% at 400 m M Na Cl,respectively.AM fungi increased the K concentration and K: Na ratio at 0m M Na Cl,while decreased the K concentration and K: Na ratio at 400 m M Na Cl.The Na concentrations of shoots and roots and Na accumulation of shoots in plants under salt conditions were increased.The plants at 400 m M Na Cl upregulated the expression of Ss NHX1,and upregulated 3-fold the expression of Ss SOS1,which promoted the Na to separate in vacuole and remove into the medium.AM fungi decreased the Na concentration of shoots under salt concentrations,and decreased the shoot/root Na ratio.AM fungi decreased the Ss NHX1 expression in the shoots and the Ss SOS1 expressions in the root,restricting Na to transference from root to shoot.AM fungi upregulated the Ss SOS1 expression in shoots and downregulated the Ss SOS1 expression and the Ss NHX1 expression in roots at 100 m M Na Cl,but AM fungi did not significantly regulate the Ss NHX1,Ss SOS1,Ss VHA-B and Ss PIP expressions at 0 m M and 200 m M Na Cl.These results implied that AM symbiosis might induce diverse modulation strategies in S.salsa,depending on external Na concentrations.The composition and structure of bacterial communities of rhizosphere of S.salsa was analyzed and a total of 32 phylum,881 genus,1649 species were detected.The dominant phyla were Proteobacteria,Actinobacteria,Cyanobacteria,Chloroflexi and Firmicutes,which accounted for more than 70%.The Sobs index was affected with salt and inoculation.AM fungi significantly decreased the Sobs index at 400 m M Na Cl and significantly increased the Shannon index at 0 m M and 100 m M Na Cl.AM fungi increased the the percentage of Proteobacteria and Actinobacteria.Further,the dominant species of mycorrhizal rhizosphere bacteria are enriched in Ramlibacter at 0 m M Na Cl,in Actinobacteria at100 m M Na Cl and in Pseudomonas and Halovulum at 400 m M Na Cl.The RDA analysis showed that the rhizosphere bacterial communities of mycorrhizal plants at 100 m M Na Cl were associated with the shoot dry weight,the root dry weight,the plant height and S-ALP.This implied that AM fungi enriched the bacterial related with the growth of plants.The transcriptome analysis showed that a total of 1316 differentially expressed genes(DEGs)in shoots were detected,and the number of upregulated genes was 381 and the number of downregulated genes was935.A total of 424 DEGs in roots were detected,and the number of upregulated genes was 194 and the number of downregulated genes was230.67.6% of the DEGs were assigned to metabolic pathways,and the carbohydrate metabolism(15.4%),energy metabolism(12.6%)and amino acid metabolism(12.0%)were assigned the more DEGs in shoots.67.5% of the DEGs in roots were assigned to metabolic pathways.The DEGs in shoots were enrichment analyzed,and “Carbon fixation in photosynthetic organisms”,“Glyoxylate and dicarboxylate metabolism”,“Porphyrin and chlorophyll metabolism”,“Cysteine and methionine metabolism”,“Circadian rhythm – plant” and “Vitamin B6 metabolism”pathways were significantly enriched.“Photosynthesis” and “Starch and sucrose metabolism” pathways were significantly enriched by the DEGs in roots.These results revealed that AM fungi affected the genes enriched in primary metabolism and photosynthesis.The proteomic analysis showed that a total of 581 differentially abundant proteins(DAPs)in shoots were detected,and the number of upregulated genes was 385 and the number of downregulated genes was196.63% of DAPs are assigned to metabolic pathways,and carbohydrate metabolism pathway(15.7%)and energy metabolism pathway(10.4%)occupied more DAPs.The results of enrichment analysis showed that“Carbon fixation in photosynthetic organisms”,“Nitrogen metabolism”and “N-Glycan biosynthesis” were enriched.These results revealed that AM fungi affected the pathways of photosynthesis and nitrogen.This study suggests that AM fungi can significantly improve the growth of S.salsa.AM fungi regulated ion balance and affected the composition and structure of rhizosphere bacterial communities,enriching rhizosphere bacteria to help the plants growth.AM fungi further regulated salt tolerance related genes and metabolic pathways so that AM fungi promoted the adaptation of salt in S.salsa under salt environments.It provides ideas and references for widening the development and utilization of salinized soil,using halophytes combined AM fungi to restore the salinized soil.