Genetic Analysis Of Potassium Efficiency In Relation To Root System Architecture In Brassica Napus L.

Potassium(K)is one of the most essential key nutrients for the plant growth.K insufficiency is connected with a weak root system,lodging,and yield losses.The root system is the fundamental driver of plant nutrition and water usage effectiveness.Developing rapeseed varieties with excellent root sytem and high K efficiency will create a considerable economic value.This study used GWAS,linkage mapping analysis and comparative transcriptome analysis to reveal the genetic mechanism of root and biomass traits of rapeseed under low K condition.The main results are as follows:1.Nine root-related and shoot biomass traits of a Brassica napus association panel were evaluated by hydroponics under low K treatment(0.01 m M K~+).The investigated traits gave significant phenotypic variations among genotypes,with heritabilities ranging from 49.4%to 60.4%.Six GWAS approaches found 453 significant SNPs(LOD≧3)that explained 12.56%of the maximum phenotypic variations.These significant associations were binned into 206 QTL clusters based on the SNPs’linkage disequilibrium r~2>0.2,including 45 pleiotropic loci.Four traits were found to be linked with two QTL clusters,q RT.A04-4 and q RT.C04-7.Within 100 kb upstream and downstream of the peak SNPs within the 45 loci,72 putative genes associated with root development were found.These putative genes were used to build a protein interaction network,which resulted in 62 genes being connected.Bna C08g29120D,Bna A09g35230D,Bna A03g06830D,Bna C04g45700D,and Bna A07g10150D were revealed to be involved in a substantial number of interactions,implying they may interplay with other genes to perform a crucial function in the family.This finding lays the framework for analyzing the genetic variations of B.napus and optimizing its root system architecture.2.According to shoot biomass weight and K utilization index(the ratio of shoot biomass weight under low k and high K treatments),20 extreme germplasm were screened from the association population and mixed to form 4 groups of materials.Each group were treated with low K(0.01 m M K~+)and high K(6 m M K~+),root samples were taken for transcription analysis at 7 and 14 days after transplant,and three biological replicates were set.The 48 libraries used generated 202 differentially expressed genes(DEGs)between the groups with low and high potassium absorption potential using a pairwise comparison approach,including phytohormone-related genes,Cytochrome P450 71B23,Glucan endo-1,3-beta-glucosidase,B-box zinc finger protein 25,Potassium transporter 5,and others.DEGs involved in glucose metabolism,lipid metabolism,amino acid metabolism,hormone pathways,and signaling pathways were essential in root development and K utilization when GO functional category and KEGG pathway analyses were combined.We also discovered 33 transcription factors(TFs)involved in root growth that were differentially expressed.3.In this study,root and biomass traits of a B.napus recombinant inbred line(RIL)population(including 236 lines)were also evaluated under low k treatment.The broad-sense heritabilities of all the investigated traits ranged from 47.74%to 72.26%.There were 56 significant QTLs associated with the traits studied,accounting for 4.79%to 16.53%of the phenotypic variances.The 56 QTLs discovered were integrated into 16 QTL clusters.The QTL cluster"qc A01-3"was detected in all three environments,suggesting that these QTLs for root development and nutrient use are genetically stable and pleiotropic.These QTLs and QTL clusters could be beneficial for using marker-assisted selection to improve numerous traits simultaneously.4.Integrating GWAS and RNA-seq Analysis,this study identified 13 common candidate genes may involve in root development regulation and K utilization.Among these,three genes encode GAPDH,CAX1 and REEILLE1,which have been reported to affect root development.Further,three common candidate genes by combining GWAS,RNA-seq,and linkage mapping analyses were discovered,also have two functional genes associated with root development.These candidate genes could provide alternative sources for molecular breeding and functional studies of rapeseed root development and K utilization efficiency.