Intellectual Merit: Seed size is important to crop domestication and fitness in natural populations and is largely affected by the balance of maternal and paternal genomes in endosperm, tissue produced inside the seeds of most flowering plants around the time of fertilization. This genome balance can be disrupted, resulting in effects on imprinted genes, expression of genes in a parent-of-origin specific manner, and seed size. In Arabidopsis thaliana, increased paternal genome dosage can result in larger seeds, whereas increased maternal genome dosage leads to smaller seeds, suggesting that the balance of maternal and paternal genomes affects endosperm and seed development. In the developing seed a major class of short-interfering RNAs (siRNAs), are maternally expressed. Genome-wide demethylation occurs in endosperm during seed development, suggesting that small RNAs serve as the factors responsible for the parental genome balance, leading to expression changes in candidate genes essential for seed development. It is likely that maternal siRNAs can regulate expression of protein-coding genes important to seed development. In this EAGER project, small RNAs and their targets that affect imprinting and seed will be characterized, the mechanism by which maternal expression of small RNAs is established will be addressed, and it will be determined when and how parent-of-origin effects are established during endosperm development.
Broader Impact: Seed production is vital to agriculture, food security, renewable resources, and human nutrition. At the mechanistic level, results from this research will reveal a novel biological role for small RNAs in regulating gene expression and seed development. Novel small RNA targets and candidate genes will be identified and characterized in this project, and the functions of selected candidates will be rigorously tested. A better understanding of how small RNAs and their targets regulate seed development will ultimately help us improve productivity and fertility of plant and animals. Plant seeds, DNA sequences, and small RNA and gene expression data will be regularly deposited to Arabidopsis Biological Resource Center (ABRC), GenBank, and Gene Expression Omnibus (GEO), respectively. Throughout the project, interdisciplinary training opportunities, including genomics, epigenetics, molecular genetics, plant biology, and computational biology, will be provided for graduate and undergraduate students in this project.