Cellular dynamics of endosperm development in Arabidopsis thaliana

Abstract

After double fertilization, the endosperm in many flowering plants undergoes repeated mitotic nuclear divisions without cytokinesis, resulting in a large coenocytic endosperm that then cellularizes. Growth during the coenocytic phase is strongly associated with the final seed size; however, detailed cellular dynamics controlling the unique coenocytic development in flowering plants have remained elusive. Integrating confocal microscopy live-cell imaging and genetics, we characterized the entire development of the coenocytic endosperm of Arabidopsis thaliana including nuclear divisions, their timing intervals, nuclear movement, and cytoskeleton dynamics. Around each nucleus, microtubules organize aster-shaped structures that drive F-actin organization. Microtubules promote nuclear movement after division while F-actin restricts it. F-actin is also involved in controlling the size of both the coenocytic endosperm and the mature seed. Characterization of cytoskeleton dynamics in real-time throughout the entire coenocyte endosperm period provides foundational knowledge of plant coenocytic development, insights into the coordination of F-actin and microtubules in nuclear dynamics, and new opportunities to increase seed size and our food security.