The Effects And Mechanisms Of S.exfoliatus FT05W Alleviating Heat Stress In Dendrobium Nobile Lindl.

Dendrobium nobile Lindl.is a perennial herb of the Orchidaceae Dendrobium genus.Due to its high medicinal and ornamental values,its market demand is increasing.However,in production,heat stress has become a bottleneck issue restricting the survival and growth of D.nobile seedlings.Therefore,it is of great significance for D.nobile cultivation and scientific management to explore the effective approaches to alleviate heat stress.Recently,it has been found that microorganisms are able to regulate plant growth,control plant diseases,and improve plant yield.Among them,some Streptomyces spp.can directly promote the growth of plants and play an important role in abiotic stresses.Moreover,utilizations of such beneficial streptomycetes are important means to reduce chemical fertilizers,pesticides inputs and potential pollutions.In our study,different concentrations of Streptomyces exfoliatus FT05W spore suspension were applied to D.nobile seedlings（cultivar:Chichai No.1）to explore their effects on host against heat stress.In addition,transcriptome and microbiome experiments were conducted to understand the mechanisms of D.nobile heat stress alleviation by S.exfoliatus FT05W.The main results and findings are as follows:（1）Application of S.exfoliatus FT05W can promote plant height,stem diameter and fresh weight of D.nobile,and promote the synthesis of alkaloids,polysaccharides and total flavonoids.The application can increase not only the activities of antioxidant enzymes such as SOD,POD,CAT and APX,but aslo the contents of soluble sugar,soluble protein and proline.In addition,it inhibites the increas of MDA content and relative conductivity,and improves the photosynthetic capacity as well.Streptomyces exfoliatus FT05W can effectively alleviate the heat stress on the growth of D.nobile seedlings,so,it play a significant role in the resistance of D.nobile seedlings to heat stress.In addition,the concentration of 1×10⁶CFU·ml^-1S.exfoliatus FT05W suspension showed the best results.（2）Under heat stress,a total of 1776 differentially expressed genes were found between“Streptomyces application group”,and“non-Streptomyces application group”.The expressions of MAPK signal pathway genes（NDPK1,PP2C,SAPK7）,photosynthesis genes（atp A,atp B,atp F,PETA,pet D,Psb C,psb D）and antioxidant enzyme pathway genes（CAT1,SODCP,PRXIIE-2）were increased.Therefore,it could be predicted that the application of S.exfoliatus FT05W assist D.nobile to maintain normal signal transduction system,photosynthetic capacity and antioxidant enzymes activities,alleviating the adverse effects of heat stress on D.nobile.（3）Both high temperature and the application of S.exfoliatus FT05W can reduce the bacterial community diversities in the D.nobile rhizosphere soil.However,the application of S.exfoliatus FT05W can optimize the structural of bacterial community in the rhizosphere,enhance the abundance of dominant bacterial such as Proteobacteria and Acidobacteria,and increased the abundance of bacterial communities involved in chloroplast membrane cell wall synthesis,nucleotide transport and metabolism.Therefore,it could be predicted that S.exfoliatus FT05W could assist D.nobile against heat stress by improving the structure of its bacterial community in the rhizosphere.