| High selenium(Se)content in soil is toxic to plants(especially plants at seedling stage).While,arbuscular mycorrhizal fungi(AMF)are important for plant stress resistance.However,the effects and mechanisms by which AMF alleviate Se stress in maize(Zea mays L.)are unclear.Therefore,a greenhouse pot experiment was design to investigate the potential influences and strategies of AMF symbiosis on Se stress alleviation in maize from plant and soil perspectives.The experiment was consisted of a completely randomized design with a factorial combination of 5 × 3,which consisted of 5 different Se content treatments(0,1,2,5,or 10 mg/kg Se)and 3 AMF treatments [non-inoculation,inoculation with Funneliformis mosseae,and/or inoculation with Claroideoglomus etunicatum].After 45 days of pots maize cultivation in greenhouse,the maize growth index,P,N,and Se accumulation,soil chemical characteristics and Se fractions were determined,and the dual RNA-Seq of maize mycorrhiza was performed.The main results are as follows:(1)The fungal colonization rates of AMF inoculated maize roots were higher than 40%.Further increase in the fungal colonization rate of F.mosseae(66.0%)were reported under the 5 mg/kg Se application treatment,which was highest among the all colonization rate in this experiment.(2)Excessive Se application(> 5 mg/kg Se)significantly inhibited leaf area,shoot height,root length,root volume,root area,root tip number,shoot dry weight and root dry weight of maize.The response of maize growth to Se stress and AM fungi was mainly observed in shoots rather than roots.AM symbiosis significantly improved root morphology,increased nitrogen and phosphorus nutrition in maize,promoted maize growth,and then diluted the content of Se in shoots(20.80-52.80%).Therefore,AMF mediated "growth-dilution" effect may be an indirect strategy to alleviate Se stress in maize.In addition,AMF significantly reduced the bioconcentration factor and translocation factor of Se,thus inhibited the transport of Se from soil/roots to shoots.(3)AMF inoculation significantly increased the easily extractable glomalin-related soil protein content and organic matter in soil,however,decreased the soluble and exchangeable Se content in soil.It also increased the organic matter-bound and residual Se content,resulting in the decrease of the bioavailable Se content in soil.(4)RNA-Seq analysis showed that AMF inoculation may attenuated the stress response of maize to Se,indicating that AM fungal symbiosis improved the Se tolerance of maize.There were 1760 differential expressed genes(DEGs)under non-inoculation,104 under F.mosseae and 536 under C.etunicatum inoculation in maize roots in response to Se stress,respectively.The analysis of GO and KEGG functional enrichment showed that the degree of functional enrichment of DEGs in inoculated maize roots under Se stress was much lower than that in non-inoculated maize roots.(5)AM symbiosis significantly down-regulated the expression of Se uptake-related ion transporter genes ZmPht2,ZmNIP2;1 and ZmSultr1;3 in maize roots,while,there was no significant effect on the expression of other transporter genes.It may lead to the relative decrease of Se uptake ability by maize roots.(6)Weighted gene co-expression network analysis found that genes related to cellular organization,cell wall,carbon transport and metabolism may be the "key genes" in maize-AMF symbioticsystem.Under Se stress,the expression of maize genes related to cellular organization,carbon transport and metabolism were significantly up-regulated,and the expression of maize genes related to cell wall were significantly down-regulated,while,the expression of AMF genes related to cellular organization were significantly up-regulated.The result indicated that Se stress may strengthen the symbiotic relationship between maize and AMF.In conclusion,AMF play an important role in alleviating Se stress in maize at seedling stage. |
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