DiSUMO-LIKE Interacts with RNA-Binding Proteins and Affects Cell-Cycle Progression during Maize Embryogenesis

Embryogenesis in flowering plants is initiated by an asymmetric zygote division, generating two daughter cells that are the precursors of different cell lineages. Little is known about the molecular players regulating activation and progression of zygote development, establishment of asymmetry, and the plant-specific process of cell-plate formation. Here, we report the function of the ubiquitin-like modifier DiSUMO-LIKE (DSUL) for early embryo development in maize. Introducing a DSUL-RNAi construct by sperm cells affects cytokinesis generating non-separated zygotic daughter nuclei or multinucleate embryonic cells lacking cell plates. DSUL accumulates in the cytoplasm partly in granules, in the nucleus, as well as in the cell division zone. The enzymatic DSULyation cascade involves maturation and the same enzymatic machinery for activation and conjugation as was previously shown for SUMO1. Identification of DSUL targets suggests predominant roles of DSULylation in regulation of cytoplasmic RNA metabolism as well as in cell-cycle progression and cell-plate formation. A comparison of DSUL and SUMO1 localization during the cell cycle and of their substrates indicates strong functional diversification between these two SUMO family modifiers. Chen et al. report that the cereal-specific SUMO variant DSUL is required during embryo cytokinesis and uses the SUMO enzymatic machinery. DSUL accumulates in cytoplasmic granules and the cell division plane, where it is preferentially conjugated to RNA-binding proteins and cell division regulators, indicating SUMO-independent function(s).