The nuclear lamina protein NEMP1 regulates tapetal programmed cell death and pollen development in rice

In land plants, tapetum development is critical for male gametophyte development. We identified the inner nuclear membrane (INM) protein OsNEMP1 in rice (Oryza sativa) as a key regulator of this developmental program. The osnemp1 mutant displays delayed tapetal programmed cell death (PCD), persistent tapetum, overaccumulation of Ubisch bodies, and defective pollen exine formation, along with complete male sterility. Expression analysis revealed the upregulation of multiple genes involved in tapetal PCD, sporopollenin biosynthesis, and pollen wall formation in osnemp1. We demonstrate that OsNEMP1 interacts with the INM proteins MAN1 and OsNEMP2 and the Ran GTPase, OsRAN2, linking it to nuclear envelope dynamics and nucleocytoplasmic transport. While OsNEMP1 and OsRAN2 both associate with the basic helix-loop-helix transcription factors TIP2 and TDR, there was no evidence for a ternary OsNEMP1-TIP2/TDR-OsRAN2 complex. Crucially, we determined that OsNEMP1 fine-tunes the transcriptional activity of the TIP2-TDR complex by tethering them at the nuclear envelope. These results suggest distinct regulatory modes for OsNEMP1-TIP2/TDR and TIP2/TDR-OsRAN2 interactions. Furthermore, OsNEMP1 may facilitate the establishment of a nuclear OsRAN2 gradient via direct interaction to modulate nucleocytoplasmic transport. Our findings identify OsNEMP1 as an essential regulator of rice male fertility, bridging nuclear envelope function to the spatial regulation of transcription during anther development.