Fig. 1: STL1 and STL2 localized to the SmaCCs/MASCs that were derived from Golgi.

a Representative images of an epidermal cell expressing both STL1-mCherry and GFP-STL2 in the basal region of 4-day-old etiolated hypocotyls. Arrows indicated colocalization at the small compartments. Bar = 2 μm. b, c Time-lapse images and kymograph analysis showing the split of GFP-STL2 signal into two (b) and the merge of two compartments into one (c). Bars = 2 μm. d, e Time-lapse images (d) and kymograph analysis (e) showing that GFP-STL2 tracked the depolymerizing ends of microtubules. Bars = 2 μm. f Representative images showing partial co-localization of tdTomato (tdt)-CesA6 and GFP-STL2 in the epidermal cells in the basal region of 4-day-old etiolated hypocotyls. Yellow arrows indicated the SmaCCs/MASCs containing both tdt-CesA6 and GFP-STL2, while white arrows indicated SmaCCs/MASCs without GFP-STL2. For analysis, region of interest (ROI) that excluded the Golgi apparatuses was marked by yellow dotted outlines. Bar = 3 μm. g, h Time-lapse images (g) and kymograph analysis (h) showing that tdt-CesA6 and GFP-STL2 co-migrated at SmaCCs/MASCs. Bars = 2 μm. i Colocalization analysis of GFP-STL2 and tdt-CesA6 in the Golgi and ROI as indicated in (f), using the Pearson correlation coefficient and Mander’s coefficient. The arrow schemes indicated the intensity overlap of GFP-STL2 with tdt-CesA6 (green) and the reversals (magenta). Values are mean ± SD. n = 11 cells from 5 seedlings; ***P value < 0.001; ns, not significant; two-sided Student’s t test. j, k Time-lapse images (j) and kymograph analysis (k) showing that the GFP-STL2 and tdt-CesA6-labeled SmaCC/MASC were directly derived from Golgi through a membrane tail-stretching process. Arrows indicated the Golgi, while the arrowheads indicated the end of the Golgi tail in (j). The progress of the Golgi membrane tail-stretching events at the indicated time points was schematically presented above the images of (j). Bars = 2 μm.