QTL Mapping And Epistasis Effect Network Construction Of Populus Euphratica Root Phenotypic Plasticity

Phenotypic plasticity is the ability of an organism to change its phenotype in response to environmental stimuli,and it plays a key role in driving biological evolution and promoting biodiversity.The genetic mechanism of how organisms dynamically regulate phenotypic plasticity through gene epistasis networks is still unclear.Populus euphratica is an important salt-tolerant plant in northwest China,and plays an important role in wind and sand control and water conservation in desert areas.The construction of a network for gene localization and gene epistasis interactions in response to salt stress in poplar roots will not only reveal the network regulatory mechanism of gene response to environmental changes and phenotypic plasticity,but also provide important theoretical and practical guidance for the selection and cultivation of high-quality salt-tolerant germplasm resources of Populus euphratica.To this end,this study used a salt stress experiment designed with Populus euphratica tissue culture clone seedlings as materials to determine the dynamic growth data of root traits.The differences in root phenotypic characteristics under different treatments were used to quantify phenotypic plasticity.Differences in root phenotypic characteristics under different treatments were used to quantify phenotypic plasticity.The QTLs in response to salt stress were identified by correlating the root phenotypic differences with high-density SNP data using a functional mapping model,and the gene effect values of each SNP locus were calculated based on the differential growth curve parameters obtained from functional mapping.The key pivotal genes and their regulatory mechanisms during the plastic response to salt stress in Populus euphratica seedling roots were analyzed based on the results of network construction,and the main findings were as follows.(1)Differential logistic growth curves were well fitted to the differential phenotypic data of different root traits of Populus euphratica under different treatments for quantitative phenotypic plasticity.(2)Functional mapping was used to correlate the differential phenotypes of different root systems with high-density SNP markers.264 QTLs were identified for all root phenotypes,and related genes were involved in biological processes such as salt stress response,growth hormone transport and antioxidant system homeostasis.(3)Functional clustering was used to classify all SNP loci of different root phenotypes into functional modules according to the differences in gene effect value expression patterns,and a functional module network was constructed.The pivotal functional modules that play key regulatory roles were found by calculating the network features.The results of gene function annotation showed that the genes in the modules were mainly involved in biological processes such as root growth,metabolic homeostasis,redox homeostasis and signal transduction.(4)Based on the gene annotation results,we constructed an epistatic regulatory network for SNPs in four pivotal functional modules closely related to phenotypic plasticity under salt stress,and identified a total of five key pivotal genes that play dynamic regulatory roles in salt stress response,redox homeostasis,and marginal genes related to root growth.In this study,we identified significant QTLs and key pivotal genes in the epistatic network of Populus euphratica root plasticity response through functional mapping and construction of epistatic network regulatory models,and analyzed their biological functions and network regulatory mechanisms of pivotal genes in the process of plasticity expression.The above findings have important theoretical and practical implications for revealing the genetic mechanism of phenotypic plasticity response of Populus euphratica root system and breeding of high-quality salt-tolerant species.