The migration of nucleolus to the nuclear periphery and the onset of homologous chromosome synapsis are characteristics of the leptotene to zygotene transition in meiocytes. Little is known about the genes regulating these processes in eukaryotes. Here we report the characterization of morphological defects in prophase I in microsporocytes in the Arabidopsis skp1-like1 (ask1-1) mutant. In ask1-1, the nucleolus of the microsporocyte failed to move to the nuclear periphery throughout prophase I, and the chromosomes failed to synapse, despite the formation of bivalents in late prophase I. We also found that the transcription of the DMC1 gene and ASY1 gene, which were predominantly transcribed prior to zygotene in microsporocytes, was not affected in ask1-1. These findings, and the fact that ASK1 is a component of the SCF ubiquitin ligase, suggest that ASK1 regulates either the leptotene to zygotene transition or events associated with the developmental transition during male meiosis in Arabidopsis.