In plants, reproductive development requires normal meiosis, which involved several highly coordinated events. Such meiotic events are regulated in a number of ways in yeast and animal systems, including transcriptional and checkpoint control mechanisms. Although a number of mutations that affect different aspects of meiosis have been characterized in plants, very little is known about the regulation of plant meiosis at the molecular level. In particular, no meiosis-specific transcriptional regulators have been identified in plants, and checkpoint control has not been observed during plant meiosis. We report here the isolation and characterization of a new Arabidopsis male-sterile mutant that exhibits meiotic defects. Meiocytes from mutant plants appeared normal up to diakinesis, when they exhibited signs of apoptosis, including defects in chromosome behavior, cytoplasmic shrinkage, and chromatin fragmentation, followed by cell death before cytokinesis. Therefore, the mutant was named male meiocyte death1 (mmd1). The MMD1 gene was cloned using Dissociation transposon tagging and encodes a plant homeo domain domain-containing protein. MMD1 is expressed preferentially during male meiosis. Our results suggest that MMD1 may be involved in the regulation of gene expression during meiosis and that the mmd1 mutation triggers cell death in male meiocytes.