NUCLEOPORIN1 mediates proteasome-based degradation of ABI5 to regulateArabidopsisseed germination

Abstract

AbstractNUCLEOPORIN1 (NUP1), a member of the Nuclear Pore Complex (NPC), is located on the inner side of the nuclear membrane. It is highly expressed in seeds; however, its role in seeds including germination has not been explored yet. Here, we identified an abscisic acid (ABA) hypersensitive phenotype ofnup1during germination. ABA treatment drastically changes the expression pattern of thousands of genes innup1, including the major transcription factors (TFs) involved in germination,ABI3,ABI4, andABI5. Double mutant analysis ofNUP1and these ABA-related genes showed that mutations inABI5can rescue the phenotype ofnup1, suggesting thatNUP1acts upstream ofABI5to regulate seed germination. ABI5, a key negative regulator of germination, is abundant in dry seeds and rapidly degrades during germination. However, its spatiotemporal regulation and interaction with other molecular players during degradation remained to be fully elucidated. We found that NUP1 is physically associated with ABI5 and the 26S proteasome. Mutation inNUP1delayed ABI5 degradation through its post-translational retention in nucleolus under abiotic stress. Taken together, our findings suggest that NUP1 anchors the proteasome to NPC and modulates seed germination through proteasome-mediated degradation of ABI5 in the vicinity of NPC in the nucleoplasm.