RESEARCH-PGR: Genomic Balance Hypothesis for Heterosis

Many major crops use hybrids between different lines to produce more robust and higher yielding plants in the field. This phenomenon is referred to as hybrid vigor or heterosis. The genetic and molecular basis of this phenomenon has been debated for over a century. This project will address the hypothesis that heterosis results from a generalized overall stimulation of gene expression in hybrids compared to their respective parents. The overall stimulation of gene expression results in larger and more cells in the hybrid than in the parents, thus producing progeny that have greater biomass. A genetic and molecular understanding of heterosis will provide the potential to improve crop production in predictable and expedited ways. If a unifying principle of heterosis can be established, it should become possible to edit plant genomes for better crop cultivation. The amount of arable land worldwide has been decreasing for several decades but the need for increased agricultural output is only increasing. The foundations established in this project will hopefully contribute to this need by providing for and advancing agricultural biotechnology through basic research. Several lines of evidence indicate that there is a transcriptome size increase in heterotic genotypes compared to their inbred parents. Generally, the expression of regulatory components is additive in hybrids and in a more stoichiometric register with each other than in their parental inbreds while the overall expression of target genes in hybrids is elevated. This project will test the hypothesis that more balanced regulatory components result in greater target gene expression. One goal will test whether RNA polymerase II has increased occupancy in hybrids as the basis of the observed increased transcriptome size. A second goal is to test whether producing unbalanced genomes in inbred and hybrid backgrounds will block or otherwise modify the heterotic response and the transcriptome size. Aneuploids for multiple regions of the maize genome will be analyzed in inbred and hybrid backgrounds for the transcriptome size and for biomass of the adult plants. The hypothesis is that imbalanced genomes will have reduced magnitude of heterosis compared to normal balanced genomes when comparing inbreds and hybrids. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.