Background: In most angiosperms, the endosperm initiates as a coenocyte and starts to cellularize after a defined number of nuclear divisions. This process of cellularization is frequently disrupted in hybrid seeds generated after crosses between different flowering plant species or plants that differ in ploidy and is thus a major obstacle to plant breeding. Restored endosperm cellularization allows researchers to rescue hybrid embryos, revealing an essential role of this process for embryo survival. Despite the importance of endosperm cellularization, why this developmental transition causes embryo arrest remained unknown.
Question: To address the functional importance of endosperm cellularization for embryo survival, we generated transcriptome data of triploid embryos that are surrounded by uncellularized endosperm and triploid embryos surrounded by cellularized endosperm.
Findings: Here we showed that embryos surrounded by an uncellularized endosperm mount an osmotic stress response that is connected to increased levels of abscisic acid (ABA) and ABA responses. By manipulating ABA biosynthesis and signaling, we revealed a causal connection between ABA-mediated osmotic stress and embryo arrest. Based on this data we propose that endosperm cellularization is required to establish dehydration tolerance in the developing embryo, ensuring survival during seed maturation. Researchers have known for decades that endosperm cellularization is essential for embryo survival, but what makes this transition relevant remained unknown. Our work provides important insights into this phenomenon.
Next steps: We found that ABA can suppress triploid seed abortion, but the detailed mechanism remains to be explored. We would like to understand the role of the ABA pathway for embryo survival by characterizing when, where, and how it acts during seed development.
Wenjia Xu, Hikaru Sato, Heinrich Bente, Juan Santos-González, Claudia Köhler (2023) Endosperm cellularization failure induces a dehydration stress response leading to embryo arrest. https://doi.org/10.1093/plcell/koac337