Actin Tug-of-War: A Novel Mechanism Regulating Seed Size by Controlling Endosperm Nuclear Positioning and Movement

Abstract

After the unique double fertilization in flowering plants, one female gamete, the central cell, undergoes nuclear divisions without cytokinesis, generating coenocytic endosperm in developing seeds. In Arabidopsis thaliana, synchronous divisions with equidistant positioning of nuclei in the endosperm support the early enlargement of the seed, securing space for the embryo to grow later. Interestingly, nuclei near the chalazal pole, opposite to the side where the embryo grows, are transported further toward the pole to establish a nuclei aggregate. Distinct actin dynamics occur within different compartments of the endosperm, and we identify that different actin isoforms are expressed in each compartment, playing a role in controlling the positioning and movement of nuclei. I will discuss our new findings on the antagonistic functions of actin dynamics mediated by actin isoforms and their regulation of final seed size determination.