Genome-wide Association Analysis Of Phenotypic Plasticity Of Heterophylly For Populus Szechuanica Var.tibetica

A genotype produces different phenotypes in different environments is called phenotypic plasticity.For some plants,the phenomenon of producing more than one kind of leaves of different sizes and forms at different locations on the same plant is called heterophylly.Because of the long life cycle of perennial woody plants,the difficulty of obtaining mutants and the complexity of genetic manipulation,suitable populations and powerful models are needed to study phenotypic plasticity of heterophylly in woody plants.The Tibetan poplar,Populus szechuanica var.tibetica,shows obvious heterophylly characteristics from the seedling stage.In this study,a natural population of Tibetan poplar containing 210 individuals was collected from the Sejila Mountains,and dense and accurate single nucleotide mutation loci(SNPs)were developed after whole genome data were obtained by secondgeneration high-throughput sequencing;the study established a phenotypic plasticity study population by asexual reproduction at two climatically different study sites in Dayi and Nantong,and digital photographs of leaves at different positions on the stem were collected.Traits such as leaf outline,leaf area,leaf length and leaf width were obtained through a high-throughput phenotype extraction process based on geometric morphological methods,and used the simplified Gielis equation to fit the leaf morphology of annual cuttings of Tibetan poplar at different positions to obtain two morphological traits,parameters l and n.The heterophylly index(HI)was introduced and modeled with a power equation to describe the response specification of heterophylly.Genomewide association analysis was performed on the phenotypic plasticity of heteromorphic leaves for different traits by a bivariate functional mapping framework.The genetic mechanism of heterophylly in Tibetan poplar was analyzed to lay the foundation for the functional genomic study of leaf morphology in Tibetan poplar.The main conclusions of this study are as follows.(1)Five phenotypic data describing leaf morphology were obtained by geometric morphometric methods combined with simplified Gielis equation.These traits were correlated with each other to different degrees,showing the biological significance of the simplified Gielis equation.(2)The phenotypes of leaves at different positions on the stem and leaves at the same position in different environments were analyzed by ANOVA,and the growth of leaves of the Tibetan poplar on the stem had the phenomenon of heterophylly,and the degree of which was different in the two environments,and the phenotypic values were generally higher in Dayi than in Nantong.It shows that the formation of heterophylly is influenced by the environment.(3)The functional relationship between leaf phenotypic values and the corresponding heterophylly index can be well fitted using a power function to describe the response specification of heteromorphic leaves.The leaf traits of Dayi and Nantong present different reaction norms with phenotypic plasticity phenomenon.For significant SNPs,the fitted parameters can be used for graphic reconstruction of heteromorphic leaves to visually display the variation of leaves.(4)Genome-wide association analysis of heteromorphic leaf traits was performed by a bivariate functional mapping model,and 483,358 high-quality SNP markers were flitered and obtained.For different traits,an average of 400 SNPs associated with phenotypic plasticity of heterophylly could be assigned,of which more than 80% could be obtained for gene function annotation.(5)The key genes regulating the phenotypic plasticity of heterophylly are mainly involved in the regulation of plant hormone signaling pathway,plant stress response,photosynthesis,plant organ development and other functions.