Genome-wide Association And Transcriptome Based Analysis Of Drought Response Mechanisms In Sunflower Seedlings

Sunflower is one of the most important oilseed crops in the world.Drought stress at the seedling stage affects yield significantly.Finding the critical genes that control drought response and using them for genetic improvement is a fast and economical way.In this study,we revealed the differences in agronomic traits,physiological and biochemical characteristics,biological processes,and metabolic pathways among different genotypes of sunflower under drought stress comprehensively through genome-wide association analysis and combined transcriptome analysis,and obtained four important candidate genes for sunflower response to drought stress,and the main results are as follows.1.drought stress resulted in a significant decrease in mean plant height and leaf area of 226 sunflower inbred lines;and a significant increase in root shoot ratio.By genomewide association analysis,a total of 80 SNP loci significantly associated with eight drought tolerance phenotypic traits were detected on all 17 chromosomes,and 118 genes were obtained within 20 kb upstream and downstream,of which 85 were protein-coding genes,64 genes were annotated,and 62 genes were found homologous in Arabidopsis.2.Two materials with different drought tolerance(drought-sensitive material K55 and drought-tolerant material K58)screened in the previous step were treated with drought stress and normal watering,respectively.Nine physiological and biochemical indices(leaf area,relative conductivity,relative leaf water content,superoxide dismutase activity,catalase activity,peroxidase activity,free proline,soluble sugar,and malondialdehyde content)were measured on days 0,7,14,and 21.The results showed that the relative conductivity,catalase activity,peroxidase activity,free proline,and malondialdehyde content continued to increase with drought stress;the relative water content continued to decrease.3.A total of 24234 differentially expressed genes(DEG)were obtained from transcriptome analysis,and the number of down-regulated genes was higher than the number of up-regulated genes at the same drought stress time point.GO analysis revealed that the common pathways enriched to the up-regulated genes on day 14 of drought stress were all related to gibberellin,and the common pathways on day 21 were all related to r RNA synthesis;the down-regulated genes on day 14 were enriched to the common GOterms were related to photosynthesis,and common GO-terms on day 21 were related to sugar and terpene metabolism.KEGG analysis revealed that up-regulated genes were enriched to γ-aminobutyric acid-related pathways(GABAergic synapse)on both day 7 and day 14 between the two species,and down-regulated genes were enriched to multiple photosynthesis-related pathways on day 14.The "Amino sugar and nucleotide sugar metabolism" pathway,"Terpenoid backbone biosynthesis " was enriched by downregulated genes at all three time points.4.WGCNA analysis revealed a high correlation between two modules(blue4,lightslateblue)and six physiological and biochemical indicators.Among them,blue4 module was positively correlated with leaf area;lightslateblue module was positively correlated with relative conductivity,catalase,peroxidase,proline,and malondialdehyde.The top 10 pivotal genes in blue4 ranked according to connectivity were functionally diverse;all pivotal genes in lightslateblue were functionally related to the ribosome.5.The joint analysis identified 18 common genes,14 of which are protein-coding genes.Among these 14 genes,three genes encode protein kinases and one gene encodes a PLATZ transcription factor.Functional analysis and literature survey revealed that all four genes are associated with the ABA-dependent drought response pathway in plants and will be used for our next in-depth analysis.