| Heterophylly,the change of leaf shape along shoot development,is a strategy for adapting to divergence environment during different stages.In Arabidopsis,mi R156-SPLs modules are identified as a hub regulator of heterophylly development.Unlike annual herb like Arabidopsis,perennial woody plants have longer history and it is more feasible to explore the mechanism of heterophylly with genetic mapping instead of genetic manipulating.However,there is few work focus on genetic association with heterophylly of leaf shape.This study focus on Populus szechuanica var.tibetica in order to explore the molecular mechanism of heteromorphic leaf development for forestry.The Tibet poplar,Populus szechuanica var.tibetica,have typical heteromorphic pattern of leaf shape,which is suitable for performing genome-wide association study for heterophylly.Here,we collected a total of 400 individuals from a natural population of Tibet poplar along an altitudinal gradient in Sejila mountain,Nyingchi,southeast of Tibet plateau.Nearly 300 thousand high quality SNP markers were obtained from next generation sequencing and utilized for GWAS analysis.Each leaf shape was fixed using a simplified Gielie equation(SGE)which has only two parameters.Then we introduced heterophylly index(HI)and power function to described the reaction norm of six leaf shape traits along heterophylly index.Finally,the GWAS analysis was performed under functional mapping framework.The main results and conclusion are listed as follows:1.A total of 290,900 high quality SNP were collected from 400 individuals using high throughput sequencing,guranting the precision for GWAS analysis.2.The population structure of individual samples illustrated that these samples divide into two altitudinal groups(High vs Low altitudinal).But the genetic divergence between these two groups were very slight(FST = 0.067)and AMOVA results indicated the little of genetic difference(3%)attributed to the difference between two groups.According to these results,there is no significant genetic divergence between high-and low-altitudinal sample group.3.By comparison its goodness and complexity with ecllipe Fourier transformation,SGE was choosing for fitting leaf shape of Tibet poplar.Then,some other leaf traits,such as leaf length,leaf width,leaf area could also be extracted based on SGE equation with very high goodness.4.We introduced a heterophylly index(HI)and it is feasible to utilize a power equation to describe the reaction norm between all six leaf shape traits and heterophylly index.An average of 1,453(1161 ～ 2790)positive SNPs associated with the heterophylly of different leaf traits.Several hub genes,including SPLs,AP2 and TCP and some other genes involved in biogenesis of different plant hormones,were identified by whole genome-wide scanning.5.Altitidudinal gradient have more effect on the heterophlly for some leaf shape traits,such as SGE parameter n and leaf area than on other traits.However,it seems that altitudinal gradients have great effect on the transfer time for heterophylly: samples from high altitude groups would transfer from juvenile into adult leaf shape quicker than those from low altitudinal group.This work is the first attemptation combining high-throughput sequencing technology and geometric method to dissect the underling genetic mechanism for heterophylly,which provide a guidance for further study. |
