Differential contributions of two domains of NAI2 to the formation of the endoplasmic reticulum body

The endoplasmic reticulum (ER) serves essential functions in eukaryotic cells, including protein folding, transport of secretory proteins, and lipid synthesis. The ER is a highly dynamic organelle that generates various types of compartments. Among them, the ER body is specifically present in plants in the Brassicaceae family and plays a crucial role in chemical defense against pathogens. The NAI2 protein is essential for ER body formation, and its ectopic overexpression is sufficient to induce ER body formation even in the leaves of Nicotiana benthamiana, where the ER body does not naturally exist. Despite the significance of NAI2 in ER body formation, the mechanism whereby NAI2 mediates ER body formation is not fully clear. This study aimed to investigate how two domains of Arabidopsis NAI2, the Glu-Phe-Glu (EFE) domain (ED) and the NAI2 domain (ND), contribute to ER body formation in N. benthamiana leaves. Using co-immunoprecipitation and bimolecular fluorescence complementation assays, we found that the ND is critical for homomeric interaction of NAI2 and ER body formation. Moreover, deletion of ED induced the formation of enlarged ER bodies, suggesting that ED plays a regulatory role during ER body formation. Our results indicate that the two domains of NAI2 cooperate to induce ER body formation in a balanced manner.

Automated summary

The endoplasmic reticulum (ER) is an essential organelle in eukaryotic cells, playing important roles in protein folding, secretory protein transport, and lipid synthesis. In plants of the Brassicaceae family, there is a specific organelle called the ER body, which is crucial for chemical defense against pathogens. The NAI2 protein is necessary for the formation of ER bodies, and even its overexpression can induce ER body formation in tobacco leaves. However, the mechanism of how NAI2 mediates ER body formation is not fully understood. This study aimed to investigate the contribution of two domains of Arabidopsis NAI2, the Glu-Phe-Glu (EFE) domain (ED) and the NAI2 domain (ND), to ER body formation in tobacco leaves. The results showed that the ND is critical for the interaction of NAI2 and the formation of ER bodies, and deletion of the ED led to the formation of enlarged ER bodies, indicating a regulatory role of the ED in ER body formation. Overall, our findings suggest that the two domains of NAI2 cooperate to induce ER body formation in a balanced manner.