Tomato Rab11a characterization evidenced a difference between SYP121-dependent and SYP122-dependent exocytosis.
The regulatory functions of Rab proteins in membrane trafficking lie in their ability to perform as molecular switches that oscillate between a GTP- and a GDP-bound conformation. The role of tomato LeRab11a in secretion was analyzed in tobacco protoplasts. Green fluorescent protein (GFP)/red fluorescent protein (RFP)-tagged LeRab11a was localized at the trans-Golgi network (TGN) in vivo. Two serines in the GTP-binding site of the protein were mutagenized, giving rise to the three mutants Rab11S22N, Rab11S27N and Rab11S22/27N. The double mutation reduced secretion of a marker protein, secRGUS (secreted rat beta-glucuronidase), by half, whereas each of the single mutations alone had a much smaller effect, showing that both serines have to be mutated to obtain a dominant negative effect on LeRab11a function. The dominant negative mutant was used to determine whether Rab11 is involved in the pathway(s) regulated by the plasma membrane syntaxins SYP121 and SYP122. Co-expression of either of these GFP-tagged syntaxins with the dominant negative Rab11S22/27N mutant led to the appearance of endosomes, but co-expression of GFP-tagged SYP122 also labeled the endoplasmic reticulum and dotted structures. However, co-expression of Rab11S22/27N with SYP121 dominant negative mutants decreased secretion of secRGUS further compared with the expression of Rab11S22/27N alone, whereas co-expression of Rab11S22/27N with SYP122 had no synergistic effect. With the same essay, the difference between SYP121- and SYP122-dependent secretion was then evidenced. The results suggest that Rab11 regulates anterograde transport from the TGN to the plasma membrane and strongly implicate SYP122, rather than SYP121. The differential effect of LeRab11a supports the possibility that SYP121 and SYP122 drive independent secretory events.
Rehman
Reiaz Ul
RU
Di.S.Te.B.A., Università del Salento, via prov. Lecce-Monteroni, 73100 Lecce, Italy.
Stigliano
Egidio
E
Lycett
Grantley W
GW
Sticher
Liliane
L
Sbano
Francesca
F
Faraco
Marianna
M
Dalessandro
Giuseppe
G
Di Sansebastiano
Gian-Pietro
GP
D015415:Biomarkers; D018744:DNA, Plant / Q000378:metabolism; D005089:Exocytosis; D005799:Genes, Dominant; D049452:Green Fluorescent Proteins / Q000378:metabolism; D015151:Immunoblotting; D018551:Solanum lycopersicum / Q000166:cytology* / Q000378:metabolism*; D050505:Mutant Proteins / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D010940:Plant Proteins / Q000378:metabolism*; D021381:Protein Transport; D011523:Protoplasts / Q000378:metabolism; D050765:Qa-SNARE Proteins / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D022142:Secretory Vesicles / Q000378:metabolism; D012995:Solubility; D020691:rab GTP-Binding Proteins / Q000378:metabolism*; D021601:trans-Golgi Network / Q000378:metabolism; D000099193:rab11 GTP-Binding Proteins
D015415:Biomarkers; D018744:DNA, Plant; D049452:Green Fluorescent Proteins; D050505:Mutant Proteins; D010940:Plant Proteins; D050765:Qa-SNARE Proteins; D011993:Recombinant Fusion Proteins; D020691:rab GTP-Binding Proteins; D000099193:rab11 GTP-Binding Proteins