Genome-Wide Association Study Of Leaf Stomatal Density And Papillae Density In Core Germplasm Of Setaria Italica

Stomata are the places where plants exchange oxygen,carbon dioxide,and water with the outside environment.They are closely related to photosynthesis and water use efficiency of plants.Papillae is not only the hydrophobic structure on the surface of plant leaves,but also an important barrier against the invasion of pathogenic.Studies on the role and development of stomata and papillae are more common in Arabidopsis and other plant species,but there are few related reports in foxtail millet.In this study,362 core germplasms of foxtail millet were selected as experimental materials and planted in Datong,Jincheng and Taigu of Shanxi Province from April to October2018,respectively.The third leaf from the top of foxtail millet plant was selected at the heading stage for counting stomatal density,big papillae density,small papillae density of the upper and lower epidermis,and then correlation analysis and feature analysis of these traits were performed in this study.Based on the data of genome re-sequencing,the six phenotypic traits and the selected high-quality single nucleotide polymorphisms(SNPs)were analyzed by genome-wide association study.In order to study the contribution of 6 leaf phenotypic traits to the drought resistance of millet,24 representative varieties were selected from the core germplasms of foxtail millet for drought resistance identification at seedling stage.The main findings are as follows:1.Analysis of epidermal structural characteristics and related traits of foxtail millet leavesThe difference of stomatal density between the upper and lower epidermis of foxtail millet leaves was very small.The density of large papilla on the upper epidermis was generally larger than that on the lower epidermis,the density of small papilla on the upper epidermis is generally smaller than that on the lower epidermis,and the upper epidermis was covered with more wax than that on the lower epidermis.The results of correlation analysis showed that the same leaf phenotypic traits had different degree of positive correlation among the three regions.2.Genome-wide association study of stomatal density and papillae density of foxtail millet leaves and prediction of candidate genesA total of 32 SNP were detected to be significantly correlated with 6 leaf phenotypic traits by genome-wide association study.All the genes in the 50 kb interval upstream and downstream of SNP sites were annotated by NR,GO and KEGG databases.Through the annotation information,a total of 9 candidate genes Si3g19240,Si3g19270,Si3g19280,Si3g19300,i3g19330,Si3g19350,Si3g19360,Si5g20890,Si2g19110 were predicted to be related to the papillae density on upper epidermis,and predicted a candidate gene Si4g14140 related to stomatal density on lower epidermis.3.Drought resistance identification of 24 foxtail millet varieties at seedling stageWe measured the plant height,stem thickness,length and width of the youngest open leaves,relative leaf water content,relative chlorophyll content,net photosynthesis rate,stomatal conductance and transpiration rate of the foxtail millet seedlings under control and drought treatment,and found that drought stress had the greatest effect on the net photosynthesis rate and transpiration rate of millet leaves at seedling stage.The drought resistance of 24 foxtail millet materials at seedling stage was divided into four grades: strong drought resistance,medium resistance,weak drought resistance and drought sensitive.However,the contribution of six leaf phenotypes to the drought resistance of foxtail millet was not determined.In summary,we analyzed the epidermal structure and phenotypic traits of foxtail millet leaves in this study.Ten candidate genes were predicted through genome-wide association study of stomatal density and papillae density of foxtail millet leaves,and then we identified the drought resistance of 24 varieties of foxtail millet at seedling stage.These results will provide the basis for the study of the epidermal structure of millet leaves,the improvement of millet traits,and the breeding of fine quality foxtail millet.