Nuclear membrane localization during pollen development and apex-focused polarity establishment of SYP124/125 during pollen germination in Arabidopsis thaliana

Elongation of the pollen tube is a highly coordinated process involving polarized secretion of cell wall and membrane materials to the apical region. We investigated changes in the localization of soluble NSF attachment proteins (SNAREs) in developing pollen grains and the pollen tube for transgenic Arabidopsis expressing pollen- specific plasma-membrane Qa-SNAREs (SYP124, 125 and 131) fused with the green fluorescent protein (GFP). The expression of SYP124 and SYP125 was firstly detected in the microspore nuclear membrane during pollen mitosis II. Although SYP124, 125 and 131 accumulated throughout the cytosol in the mature pollen grain, GFPSYP124 and GFP-SYP125 were highly concentrated in the apical or subapical regions of the elongating pollen tube with slightly different localization patterns, whereas GFP-SYP131 was uniformly localized to the plasma membrane of the pollen tube. The apex-focused polarity of GFP-SYP125 was established coincident with formation of a Ca2+ gradient before pollen germination. These results suggest that SNAREs function differentially in the same cells and that at least two distinct membrane transport pathways are involved in the pollen development and the pollen tube germination and elongation.