Gene Regulatory Networks in the Maize Endosperm

PI: Ramin Yadegari (University of Arizona)

CoPIs: Philip W. Becraft (Iowa State University), Joanne M. Dannenhoffer (Central Michigan University), and Gary N. Drews (University of Utah)

Endosperm is a major component of the seed, and is biologically and economically important. In all angiosperms, endosperm provides nutrients and signals to the embryo during seed development. In cereal grains, endosperm composes a large proportion of the mature seed, and contains large amounts of carbohydrates and proteins, which provide more than 50% of the calories in the human diet, either directly or indirectly through animal feed. Cereal endosperm also serves as a raw material for manufacturing important industrial products, including ethanol. Maize is an excellent model system for molecular genetic analysis of cereal endosperm and is the primary subject of this research project which focuses on maize early endosperm development, encompassing the time when the endosperm grows from a single cell into a multicellular structure composed of different specialized cell types. Although the molecular mechanisms that control this developmental period have not been elucidated, they are likely to affect many economically important processes including, but not limited to, the regulation of seed size, and accumulation of starch and protein during grain filling. In addition to the training of students and postdoctoral associates, the project will provide summer research training internships for undergraduate students from Central Michigan University.

To identify genetic pathways that control endosperm cell differentiation, gene expression profiling will be performed on each endosperm cell type at multiple time points; this will be accomplished through a combination of laser-capture microdissection to collect specific endosperm cell types and the RNA-seq method (high throughput sequencing of cDNA) to identify all the genes expressed in the collected tissues. This information will be used as a framework for gene-network analysis in two of the endosperm cell types: the starchy endosperm and basal transfer layer. Starchy endosperm is the major repository for starch and protein accumulation, while the basal transfer layer is important for transporting sugar and amino acid building blocks into the growing grain; both tissues are important for grain yield and quality. The gene networks will be revealed by performing gene co-expression analysis and key transcription factors will be studied with protein-DNA assays and genetic analyses. Early endosperm development is highly sensitive to drought stress which can decrease grain yield, even if favorable moisture conditions are restored. To identify the gene-expression perturbations caused by drought stress in maize kernels, gene expression profiling will be performed with kernels from drought-stressed plants. In addition, this project will profile the genes expressed during early endosperm development in a closely related cereal, sorghum, and use comparative genomics with maize to reveal fundamental and species-specific aspects of endosperm development. Data generated can be accessed through the project website (www.grainendosperm.org) as well as through long-term repositories such as MaizeGDB and NCBI's GEO and SRA.