Novel ankyrin-repeat mutant and modifiers of a kafirin mutant improve sorghum protein digestibility

Sorghum is a staple food for over 500 million people in Sub-Saharan Africa and Asia, however, sorghum proteins are poorly digested when wet-cooked. Three sorghum mutants were identified in a mutagenized population of the inbred line BTx623 that showed a 23-37% increase in wet-cooked protein digestibility compared to their unmutagenized parent. Furthermore, in comparison to the known high lysine, highly digestible sorghum mutant, P721Q, these mutants had 9% more protein overall that was 10% more digestible, had 12% more lysine, as well as better seed hardness. Using bulked segregant analysis based on whole genome sequencing data, we identified unique genomic regions on chromosome 5 of each EMS mutant that are associated with the increase in protein digestibility. Analyzing shared mutations in candidate genes, the high protein digestibility phenotype in one mutant is linked to a point mutation in a novel, ankyrin repeat protein. In another, the increase is associated with a mutation in a kafirin gene and suggests novel genetic modifiers. This study provides material and molecular markers that can be used to enhance sorghum nutritional value, contribute to fighting malnutrition and elucidate new roles for ankyrin-repeat proteins in plants.