GRAIN GAINS: DISSECTING THE GENETIC NETWORK LIMITING GRAIN PRODUCTION IN MAIZE AND ITS CROP RELATIVES

Carpel suppression occurs in at least half of every flower produced by grasses in the Panicoideae subfamily, which includes maize and the climate-resilient millets. Carpel suppression limits potential grain production and crop yield. Therefore, carpel suppression genes represent promising genome editing targets to increase yield in panicoid crops. The major goal of this project is to identify genes that regulate carpel suppression in maize and its relatives in the Panicoideae, and to determine how these genes are ordered into genetic pathways. To achieve this goal, we will (Objective 1) determine the genetic underpinnings of carpel suppression, and dramatically increase the number of known maize carpel suppression genes; (Objective 2) determine interactions between genetic pathways regulating carpel suppression in maize; and (Objective 3) determine the roles for homologs of maize carpel suppression genes in setaria. This project will also contribute to agricultural education, by training a postdoctoral researcher, a graduate student, and at least two undergraduate researchers. This fundamental understanding of the genetics of carpel suppressionIn Objective 1, we will use bulked segregant analysis coupled to high-throughput sequencing to map the genes underlying 40 carpel suppression mutants, and quantify their morphological phenotypes. Depending on our mapping and phenotyping results, we will clone a subset of these mutant genes. This objective is expected to involve all participants, to start immediately, and be completed in the final half of the third year of the project period.In Objective 2 we will (1) order select carpel suppression genes into genetic pathways; (2) define the genetic modules and pathways regulating carpel suppression; and (3) identify carpel suppression gene candidates that can be explored in crop improvement efforts. To achieve these sub-objectives, we will perform three sets of experiments: (1) phytohormone rescue experiments, (2) phytohormone and sugar measurements, and (3) transcriptomics experiments. This objective is expected to involve the graduate student or postdoc, undergraduates, collaborators, and the PD. Experiments associated with this objective will start in the second half of the first year, and be completed in the final half of the third year of the project period.In Objective 3, we will test the hypothesis that carpel suppression is mediated by homologous genes across the panicoids. To do this, we will make and characterize mutants of maize carpel suppression gene homologs using CRISPR-Cas9 genome editing in setaria, which is distantly related to maize. This objective is expected to involve the graduate student or postdoc, undergraduates, collaborators, and the PD. Experiments associated with this objective will start immediately, and be completed by the end of the project period.