| Summary: | The secretory pathway of plant cells consists of several organelles that are connected by vesicle and tubular transport. Every compartment has a distinct function and the specificity of vesicle fusion is essential to maintain the organelles identity. N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) play a crucial role in the secretory pathway driving specific vesicle fusions. A vesicle SNARE (v-SNARE) on a vesicle specifically interacts with two or three target SNAREs (t-SNAREs) on the target compartment. This event leads to vesicle membrane fusion with the membrane of the target compartment and the release of cargo molecules into the organelle lumen.<p>
The aim of this work was the characterization of two <i>Arabidopsis thaliana</i> SNAREs. The first one is a v-SNARE, Bet11 that is the Arabidopsis ortholog of the yeast and mammal ER-Golgi v-SNARE, Bet1. In these organisms, Bet1 is involved in trafficking between the ER and Golgi apparatus. The second protein studied is a putative SNARE called Bet12 that shares high sequence identity with Bet11. In particular, I was interested in studying the sorting of these two proteins and their role in the secretory pathway of plant cells. By confocal laser microscopy, I demonstrated that these two proteins have different intracellular localization: Bet11 was mainly localized on the ER, Golgi stacks and punctate structures that I have identified as endosomes. Bet12 was localized only on the Golgi stacks. The identification of signal(s) involved in targeting of Bet11 and Bet12 were studied. To reach this aim I generated different mutant chimeras of Bet11 and Bet12. The co-expression of these chimeras with specific protein markers suggested that the distribution of these proteins was the result of a combined influence of multiple domains.<p>
A serine in the Bet11 sequence was identified as a putative phosphorylation site and appeared important for proper Bet11 intracellular distribution.<p>
The different intracellular distributions of Bet11 and Bet12 suggest different biological roles for the two proteins. To functionally characterize these two proteins homozygous knock-down mutants of Bet11 were screened. These plants had no evident phenotype, suggesting a possible genetic redundancy in this SNARE family.
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