Functional genomics of sorghum grain quality traits
Sorghum is one of the most prominent cereal crops in semi-arid environments around the world, ranking fifth in global cereal production. It is a staple crop in sub-Saharan Africa where it is used to make traditional food products like porridge or beer. Grain quality influences how sorghum can be utilized by food processors and direct consumers. Starch content and composition have a strong influence on end-use quality. The proportions and fine structures of amylose and amylopectin, as well as starch gelatinization and retrogradation properties are known to affect the functionality of sorghum in food applications. While the genetic controls of these properties have been widely attributed to the starch biosynthesis pathway in related cereals such as maize and rice, these genes have not been well characterized in sorghum with the exception of the gene for waxy. Utilizing a population of 600 sequence-indexed EMS mutants and a bioinformatics pipeline, a reverse genetic approach was employed to identify putative starch biosynthesis mutants. Leveraging knowledge of orthologous genes in related species, I characterized a set of sorghum mutants for an array of starch properties thought to be affected by the mutations of interest. This approach allowed for the identification and characterization of candidate genes in sorghum for starch synthase II (SSII) and starch synthase III (SSIII) as well as a new allele of the granule bound starch synthase I (waxy) gene. The putative SSII and SSIII mutants exhibited novel low gelatinization temperature and high amylose phenotypes that aligned with descriptions of orthologous genes in rice, maize, and other related species. In a second study, single nucleotide polymorphism (SNP) markers were designed and validated for the putative mutations in SSIII. Subsequently, genetic linkage was established for SSIII by linking proposed causative SNPs and high amylose phenotypes in segregating M2 families. In the final study, I adapted the alkali spread value (ASV) test, which is commonly employed in rice, for use in sorghum. The high-throughput method was able to easily distinguish the low gelatinization temperature phenotype in the previously identified SSII mutant. Using the ASV method, additional populations of sorghum were screened, and a second putative SSII EMS mutant was identified. In future studies, the ASV method can be utilized as a high-throughput assay to further study and characterize the SSII gene and low gelatinization temperature trait in sorghum.
Tuinstra, Purdue University.
Agronomy|Food Science|Plant sciences
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