Differential expression control and polarized distribution of plasma membrane-resident SYP1 SNAREs in Arabidopsis thaliana.

Membrane trafficking to the plasma membrane (PM) is a highly organized process which enables plant cells to build up their bodies. SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) genes, which encode the proteins involved in membrane trafficking, are much more abundant in the Arabidopsis genome than in that of any other eukaryote. We have previously shown that a large number of SNARE molecules in the Arabidopsis cell are localized predominantly on the PM. In the present study, in order to elucidate the physiological function of each PM-localized SNARE, we analyzed the spatiotemporal expression profiling of nine SYP1s that are resident in the PM of Arabidopsis, and used the information thus acquired to generate transgenic Arabidopsis plants expressing green fluorescent protein-fused Qa-SNAREs under control of their authentic promoters. Among the nine SYP1s, only SYP132 is expressed ubiquitously in all tissues throughout plant development. The expression patterns of the other SYP1s, in contrast, are tissue specific, and all different from one another. A particularly noteworthy example is SYP123, which is predominantly expressed in root hair cells during root development, and shows a focal accumulation pattern at the tip region of root hairs. These results suggest that SYP132 is involved in constitutive membrane trafficking to the PM throughout plant development, while the other SYP1s are involved in membrane trafficking events such as root formation or tip growth of root hair, with some redundancy.