Tethering LDs to ER by Rab18/NRZ/SNARE complex controls LD growth. (A) Representative EM images showing a close contact between ER and LD in Rab18 overexpressing cells. ER cisternae are indicated with blue arrow; ER–LD contact sites are indicated with red arrows. Bars: (1–5) 500 nm; (6) 1 µm; (insets) 100 nm. (B) Quantification of percentage of cells containing APEX-Stx18–positive ER–LD contact (22–39 cells/genotype, pooled from two experiments). (C) Quantification of percentage of LDs apposing to ER per ROI. Mean ± SD; n = 11–17 ROIs/genotype; ***, P < 0.001 by two-tailed t test. (D) Quantification of percentage of LD surface area apposing to ER per ROI. Mean ± SD; n = 11–17 ROIs/genotype; ***, P < 0.001 by Mann-Whitney test. (E) Working model: Rab18-GTP binds to the NRZ tethering complex and its associated Q-SNAREs to recruit ER to the close proximity of LDs to create a contact between ER and LDs, allowing the transfer of TAG from ER to LDs at the interface of ER–LD to promote nascent LD growth. All experiments were performed at least twice. O.E., overexpression.