Natural Variation in Synthesis and Catabolism Genes Influences Dhurrin Content in Sorghum

Abstract

Cyanogenic glucosides are natural compounds found in more than 1000 species of angiosperms that produce HCN and are deemed undesirable for agricultural use. However, these compounds are important components of the primary defensive mechanisms of many plant species. One of the best-studied cyanogenic glucosides is dhurrin [(S)-p-hydroxymandelonitrile--D-glucopyranoside], which is produced primarily in sorghum [Sorghum bicolor (L.) Moench]. 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 study (GWAS) using a panel of 700 diverse converted sorghum lines (conversion panel) previously subjected to pre-breeding and selected for short stature (~1 m in height) and photoperiod insensitivity. The conversion panel was grown for 2 yr in three 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. A GWAS using a mixed linear model revealed significant associations (a false discovery rate [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 was associated consistently with biosynthetic genes in the two N-fertilized environments, while dhurrin content was associated with catabolic loci in the environment without supplemental N. These results suggest that genes for both biosynthesis and catabolism are important in determining natural variation for leaf dhurrin in sorghum in different environments.

Discovery of a Dhurrin QTL in Sorghum: Co‐localization of Dhurrin Biosynthesis and a Novel Stay‐green QTL

“…Because sorghum is also used for forage, selection against high levels of dhurrin in these materials may have contributed to enrichment of these haplotypes in the elite sorghum breeding germplasm. Alleles contributing to low dhurrin level in BTx406 help explain results from a recent association study based on analysis of dhurrin levels in lines derived from the sorghum conversion program (Hayes et al, 2015). The same region of SBI01 identified here was associated with variation in dhurrin level along with a region on SBI08 that aligned with genes encoding dhurrinase (Hayes et al, 2015).…”

“…Dhurrin levels in most of these genotypes were confirmed by analysis of plants grown in Lubbock‐AgriLife in 2013 (Table 4). Hayes et al (2015) reported an association between dhurrin levels and markers in this same region of SBI01 based on data collected from genotypes from the sorghum conversion (SC) program that were converted for the most part, by introgression with the four‐dwarf line BTx406. The dhurrin gene sequence variants present in BTx406 were identical to those found in Tx7000, consistent with this genotype being a source of alleles for low dhurrin in some of the converted lines.…”

“…Two genes encoding dhurrinases, enzymes that mediate the first step in catabolism, are present on chromosome 8 (SBI08). Hayes et al (2015) identified extensive variation for dhurrin content within a large set of sorghum conversion (SC) lines, and using genome wide association study (GWAS), found significant associations between variation in leaf dhurrin levels and regions of SBI01 and SBI08 respectfully, encoding enzymes for dhurrin synthesis and turnover.…”

Composition, functional components, and physical characteristics of grain from staygreen and senescent sorghum lines grown under variable water availability

“…The John Burke (JB) lines were developed from Ethiopian lines that maintained green leaves (a staygreen trait) at the lower levels of the canopy under low light conditions. The sorghum conversion lines (SC) were selected based on their dhurrin levels by Hayes et al., (high dhurrin content; SC1154‐14E, SC335, SC54, SC56, SC599, and SC110, low dhurrin content; SC191, SC270, SC774, and SC1506). SC1506 is also a determined senescent line.…”

Early Seedling Growth Characteristics Relate to the Staygreen Trait and Dhurrin Levels in Sorghum

“…postflowering drought tolerance in sorghum has been linked to the staygreen trait and associated with increased grain yield during postanthesis stress. Because of the observed associations between staygreen and dhurrin levels, based on dhurrin content determined from leaves of matured plants (Burke et al, 2013;Hayes et al, 2015), efficient selection for dhurrin levels in grain sorghum germplasm will be an important component in breeding for improved postflowering drought tolerance. Differences in dhurrin content between high and low dhurrin levels lines is only markedly favored to the high dhurrin level lines in the upper leaves of matured field-grown plants.…”