Replicate and die for your own good: Endoreduplication and cell death in the cereal endosperm

Abstract

Development of the cereal endosperm involves different stages that include cell proliferation, endoreduplication, the biosynthesis and accumulation of storage compounds, and programmed cell death (PCD). During endoreduplication, repeated genome duplications without mitosis or cytokinesis result in large polyploidy nuclei. Endoreduplication is affected by genetic, epigenetic, hormonal and environmental factors, as well as by several cell cycle-controlling genes. Although endoreduplication is strongly correlated with an increase in cell size, the accumulation of storage reserves, and high metabolic rates, its exact role(s) in endosperm development has not been demonstrated.Two distinct PCD types take place in the endosperm. In the starchy endosperm, cells undergo PCD during the maturation phase of seed development, but their corpses are largely retained until germination. Aleurone cells, instead, remain alive throughout endosperm development, but they die and disassemble as a result of the activation of a specific autolytic program during germination. Hydrolases released by dying aleurone cells help digest and remobilize the storage compounds in the starchy endosperm to support seedling development. Although cell death programs in the starchy endosperm and aleurone are characterized by different mechanisms and regulation, the balance between cell death-promoting and -repressing hormones plays a key role in both systems.