Dynamic changes in chromatin structure and transcriptional activity in the generative cells of Lilium longiflorum

Pollen is required for fertilization and the associated production of seeds and fruits, which are important for human nutrition. Research on the tricellular pollen of Arabidopsis thaliana revealed that chromatin is highly condensed and transcriptional activity is suppressed in sperm cells. However, comprehensive structural investigations involving generative cells of bicellular pollen have not been conducted. In this study, we provide relevant insights into other angiosperms that produce bicellular pollen. Lilium longiflorum, which has large and easily observable nuclei, was used for a detailed analysis of the chromatin structure and transcriptionally active regions in pollen and pollen tubes. Chromatin was condensed, resulting in a ribbon-like structure that was clearly visible in mature generative cell nuclei. Additionally, transcriptionally active regions were restricted to the intersections of chromatin as pollen desiccated. Although de novo transcription was revealed to be unnecessary for pollen tube growth, transcriptional activity temporarily resumed before generative cell division during pollen tube growth. Moreover, the inhibition of de novo transcription influenced changes in nuclear morphology. In this study, the distinctive chromatin structures and transcriptional activity states in generative cell nuclei of bicellular pollen were elucidated, with the generated data contributing to a deeper understanding of transcription and other regulatory mechanisms involved in pollen maturation and pollen tube growth.