A novel male-sterile mutant of Arabidopsis thaliana was isolated by means of T-DNA tagging. Pollen abortion of the mutant was evident after microspore release, and pollen grains were completely absent at anthesis. Transmission electron microscope analysis revealed that primexine was coarsely developed, and that although sporopollenin was produced, it was not deposited onto the microspore plasma mem- brane. The sporopollenin that failed to be deposited aggregated and accumulated within the locule and on the locule wall. Finally, as no exine formation was observed, the mutant was named nef1. The plastoglobuli within the plastids of the tapetum were reduced, and lipid accumulation was considerably decreased. The mutant had a signi®cantly altered leaf chloroplast ultrastructure and showed various growth defects. Lipid analysis revealed that the total lipid content in nef1 was lower than that in the wild type, which indicated that Nef1 was involved in lipid metabolism. Cloning of the full-length Nef1 indicated that the gene encodes a novel plant protein of 1123 amino acids with limited sequence similarities to membrane proteins or transporter-like proteins, and the NEF1 is predicted to be a plastid integral membrane protein. Motif ana- lysis revealed that NEF1 contains prokaryotic membrane lipoprotein lipid attachment sites that are involved in maintaining cell envelope integrity. It is predicted that the Nef1 encodes a membrane protein that maintains the envelope integrity in the plastids.