|Brown, Patrick - University Of Illinois|
|Thurber, Carrie - University Of Illinois|
Submitted to: The Plant Genome
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/17/2014
Publication Date: 7/10/2015
Citation: Hayes, C.M., Burow, G.B., Brown, P., Burke, J.J., Xin, Z., Thurber, C. 2015. Natural variation in synthesis and catabolism genes influences dhurrin content in sorghum (Sorghum bicolor L. Moench). The Plant Genome. 8(2):1-9.
Interpretive Summary: Dhurrin is a type of natural product found in sorghum leaves that belongs to the group referred to as “cyanogenic glucosides”. The presence of dhurrin is commonly understood to be undesirable due to production of prussic acid (HCN), but this compound plays an important role in sorghum, specifically for overall defense against insect and pathogen attack, as a nitrogen reserve, and as a compound used to tolerate unfavorable conditions like water stress. To date there is inadequate data and understanding that could explain the differences between varieties or why some accession and varieties of sorghum produce more dhurrin compared to other lines. This research dealt with the study of differences in dhurrin production between 700 unique lines of sorghum to understand the genetic factors contributing to variation. Results showed that high dhurrin producing lines are found in the Caudatum group of sorghum. A comprehensive comparative study of the overall genome known as “genome wide association study “ showed that genetic factors involved in both production and breakdown of the compound play important roles in determining differences in dhurrin content in sorghum leaves. From this study, 19 genetic markers (in the form of single nucleotide polymorphism, “SNP”) associated with dhurrin accumulation in sorghum were identified. These genetic markers offer extensive information on the genetic blueprint of the differences in leaf dhurrin content between sorghum lines. The SNP markers also provide insight on how supplemental nitrogen can affect genetic factors involved in determining dhurrin levels among sorghum lines.
Technical Abstract: Cyanogenic glucosides are natural compounds found in over 1,000 species of angiosperms that produce HCN and are deemed undesirable for agricultural use. However, these compounds are important components of primary defensive mechanisms of many plant species. One of the best-studied cyanogenic glucosides is dhurrin ([(S)-p-hydroxymandelonitrile-ß-D-glucopyranoside]), which is produced primarily in sorghum (Sorghum bicolor L. Moench) leaves. The biochemical basis for dhurrin metabolism is well established, however, little information is available on its genetic control. Here, we dissect the genetic control of leaf dhurrin content through a genome-wide association analysis (GWAS) using a panel of 700 diverse converted sorghum lines(conversion panel) previously subjected to pre breeding and selected for short stature ( ~ 1m height) and photoperiod insensitivity. The conversion panel was grown for two years in two environments. Wide variation for leaf dhurrin content was found in the sorghum conversion panel, with the caudatum group exhibiting the highest dhurrin content and the guinea group showing the lowest dhurrin content. GWAS using a mixed linear model revealed significant associations (FDR<0.05) close to both UGT 185B1 in the canonical biosynthetic gene cluster on chromosome 1 and close to the catabolic dhurrinase loci on chromosome 8. Dhurrin content associated consistently with biosynthetic genes in the two nitrogen-fertilized environments, while dhurrin content associated with catabolic loci in the environment without supplemental nitrogen. These results suggest that both genes for biosynthesis and catabolism are important in determining natural variation for leaf dhurrin in sorghum in different environments.