Genetic Perturbation of the Starch Biosynthesis in Maize Endosperm Reveals Sugar-Responsive Gene Networks

In maize, starch mutants have facilitated characterization of key genes involved in endosperm starch biosynthesis such as ( ) and ( ). While many starch biosynthesis enzymes have been characterized, the mechanisms of certain genes (including ) are yet undefined, and very little is understood about the regulation of starch biosynthesis. As a model, we utilize commercially important sweet corn mutations, and , to genetically perturb starch production in the endosperm. To characterize the transcriptomic response to starch mutations and identify potential regulators of this pathway, differential expression and coexpression network analysis was performed on near-isogenic lines (NILs) (wildtype, , and ) in six genetic backgrounds. Lines were grown in field conditions and kernels were sampled in consecutive developmental stages (blister stage at 14 days after pollination (DAP), milk stage at 21 DAP, and dent stage at 28 DAP). Kernels were dissected to separate embryo and pericarp from the endosperm tissue and 3' RNA-seq libraries were prepared. Mutation of the gene led to minimal changes in the endosperm transcriptome. Responses to loss of function include increased expression of sugar (SWEET) transporters and of genes for ABA signaling. Key regulators of starch biosynthesis and grain filling were identified. Notably, this includes Class II trehalose 6-phosphate synthases, , and transcription factor-like (AP2/ERF) transcription factors. Additionally, our results provide insight into the mechanism of , suggesting a potential role in regulating GA signaling via GRAS transcription factor .