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

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-ß-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.

Genetic analysis of recombinant inbred lines for Sorghum bicolor × Sorghum propinquum.

We describe a recombinant inbred line (RIL) population of 161 F5 genotypes for the widest euploid cross that can be made to cultivated sorghum (Sorghum bicolor) using conventional techniques, S. bicolor × Sorghum propinquum, that segregates for many traits related to plant architecture, growth and development, reproduction, and life history. The genetic map of the S. bicolor × S. propinquum RILs contains 141 loci on 10 linkage groups collectively spanning 773.1 cM. Although the genetic map has DNA marker density well-suited to quantitative trait loci mapping and samples most of the genome, our previous observations that sorghum pericentromeric heterochromatin is recalcitrant to recombination is highlighted by the finding that the vast majority of recombination in sorghum is concentrated in small regions of euchromatin that are distal to most chromosomes. The advancement of the RIL population in an environment to which the S. bicolor parent was well adapted (indeed bred for) but the S. propinquum parent was not largely eliminated an allele for short-day flowering that confounded many other traits, for example, permitting us to map new quantitative trait loci for flowering that previously eluded detection. Additional recombination that has accrued in the development of this RIL population also may have improved resolution of apices of heterozygote excess, accounting for their greater abundance in the F5 than the F2 generation. The S. bicolor × S. propinquum RIL population offers advantages over early-generation populations that will shed new light on genetic, environmental, and physiological/biochemical factors that regulate plant growth and development.

Molecular mapping and characterization of BLMC, a locus for profuse wax (bloom) and enhanced cuticular features of Sorghum (Sorghum bicolor (L.) Moench.).

Sorghum is distinct from other cereal crops due to its ability to produce profuse amount of epicuticular wax (EW or bloom) on its culm and leaves along with less permeable cuticle which are considered to be important traits contributing to abiotic stress tolerance. Here, we report the molecular mapping and characterization of BL OO M-C UTICLE (BLMC), a locus associated with production of profuse wax, using a mutant mapping population developed from a cross between BTx623 (wild type with profuse wax) and KFS2021 (a mutant with greatly reduced wax). The F2 progenies were genotyped using known and newly developed microsatellite markers to establish a molecular map of BLMC. The locus mapped to a 3.6-centimorgans (cM) interval in the terminal end of sorghum chromosome 10 with flanking markers Xsbarslbk10.47 and Xcup42. Targeted mapping delimited BLMC to as small as 0.7 cM region and facilitated identification of three cosegregating markers with the trait. The BLMC region corresponds to approximately 153,000 bp and candidate genes identified include among others an acyl CoA oxidase (a gene involved in lipid and wax biosynthesis) and seven other putative transcripts. Phenotypic characterization showed that in addition to disrupting the EW production, BLMC mutation reduced culm and leaf cuticle, increased plant death rating in the field at anthesis and significantly reduced the C:28 to C:30 free fatty acid fractions of culm and leaf EW. These results clearly support the important role of BLMC in the expression of profuse wax and enhanced cuticular features of sorghum. Genetic mapping of BLMC opened avenues for identification of genes involved in the cuticle/wax pathway of sorghum and their application for improvement of abiotic stress tolerance.