Accessory B Chromosomes Alter Chromatin Accessibility and Gene Expression in Maize Pollen Nuclei

Abstract

B chromosomes in maize (Zea mays L.) are supernumerary, nonessential chromosomes that exhibit non-Mendelian inheritance through chromosome drive. During the second pollen mitosis, they undergo nondisjunction, resulting in their preferential transmission via B-containing sperm cells. Although their transmission mechanisms have been extensively characterized, the effects on chromatin organization and transcriptional regulation in gametophytic cells remain poorly understood. Here, we combined flow cytometric sorting of pollen nuclei with an assay for transposase-accessible chromatin sequencing (ATAC-seq) and RNA sequencing (RNA-seq) to investigate the impact of B chromosomes on chromatin accessibility and gene expression in mature maize pollen. Using pollen nuclei isolated from a maize inbred line B73 carrying zero and two B chromosomes, we generated high-purity datasets suitable for integrated chromatin and transcriptomic analyses. We identified extensive chromatin accessibility and transcriptional activity at B-chromosome loci. Importantly, the presence of B chromosomes was also associated with altered chromatin accessibility and gene expression on the standard A chromosomes, revealing regulatory effects extending beyond the B chromosome itself. Together, these findings contribute to a broader understanding of effects of selfish genetic elements in plants.