MATERNAL CONTROL OF SEED SIZE IN ARABIDOPSIS

Abstract

In Arabidopsis, seed size could be regulated either maternally through integument development or zygotically through endosperm or embryo development. Here we demonstrate that TERMINAL FLOWER1 (TFL1) has a maternal effect of sporophytic origin on endosperm cellularization and seed size. Loss of function of TFL1 results in large seeds with delayed peripheral endosperm cellularization. TFL1 mRNA is specifically expressed in the chalazal endosperm, whereas TFL1 protein is only detectable in the peripheral endosperm, indicating that TFL1 functions as a mobile signal in developing seeds. We further show that RAN proteins interact with TFL1 to prevent its transport from the chalazal endosperm to peripheral endosperm. In the peripheral endosperm, TFL1 is involved in mediating ABA signaling by regulating ABI5 protein stability during early seed development. Taken together, our findings provide new insights into the mechanism by which TFL1 mediates the maternal effect on endosperm cellularization, thus affecting the seed size.