KIL1 and KIL2 promote endosperm elimination in maize

The endosperm is a nutritive tissue that supports the growing embryo. Endosperm life span is restricted to seed development and germination. During maize kernel development in maize, two distinct endosperm cell death processes occur. The endosperm adjacent to the embryo scutellum (EAS) undergoes a lytic cell death supposedly to allow embryo expansion, whereas the starchy endosperm (SE) dies after kernel filling producing cell corpses that store nutrients required during germination. Here, we present a detailed analysis of these divergent cell death processes. During SE cell death, mitochondria, nuclei, and the endoplasmic reticulum disintegrate, while nuclear chromatin, cell walls, starch granules, and protein bodies are preserved. In contrast, EAS cells remobilize their stored nutrients, secrete extracellular vesicles, before the cells collapse and a complex post-mortem corpse clearance process ensues. Using single-nucleus RNA-sequencing transcriptome analysis of the developing endosperm, we identified the NAC transcription factors KIL1 and KIL2 as specifically expressed in the EAS. Dominant and recessive loss-of-function approaches demonstrate that KIL1 and KIL2 redundantly promote cell death execution and corpse clearance of the EAS, but are not required for SE cell death. The reduction of EAS cell death in loss-of-function lines strongly impeded embryo growth. Interestingly, KIL1 and KIL2 expression are promoted by DED1, an imprinted paternally expressed transcription factor, suggesting a paternal control over EAS cell death and embryo growth in maize. To investigate the consequence of KIL1 and KIL2 loss of function we carried out an RNA-seq on EAS enriched endosperm, 19 days after pollination