Divergent functions of VTI12 and VTI11 in trafficking to storage and lytic vacuoles in Arabidopsis.
The protein storage vacuole (PSV) is a plant-specific organelle that accumulates reserve proteins, one of the main agricultural products obtained from crops. Despite the importance of this process, the cellular machinery required for transport and accumulation of storage proteins remains largely unknown. Interfering with transport to PSVs has been shown to result in secretion of cargo. Therefore, secretion of a suitable marker could be used as an assay to identify mutants in this pathway. CLV3, a negative regulator of shoot stem cell proliferation, is an extracellular ligand that is rendered inactive when targeted to vacuoles. We devised an assay where trafficking mutants secrete engineered vacuolar CLV3 and show reduced meristems, a phenotype easily detected by visual inspection of plants. We tested this scheme in plants expressing VAC2, a fusion of CLV3 to the vacuolar sorting signal from the storage protein barley lectin. In this way, we determined that trafficking of VAC2 requires the SNARE VTI12 but not its close homologue, the conditionally redundant VTI11 protein. Furthermore, a vti12 mutant is specifically altered in transport of storage proteins, whereas a vti11 mutant is affected in transport of a lytic vacuole marker. These results demonstrate the specialization of VTI12 and VTI11 in mediating trafficking to storage and lytic vacuoles, respectively. Moreover, they validate the VAC2 secretion assay as a simple method to isolate genes that mediate trafficking to the PSV.
Sanmartín
Maite
M
Departamento de Genética Molecular de Plantas, Centro Nacional de Biotecnología, Consejo Superior de Investigaciones Científicas, E-28049 Madrid, Spain.
Ordóñez
Angel
A
Sohn
Eun Ju
EJ
Robert
Stephanie
S
Sánchez-Serrano
José Juán
JJ
Surpin
Marci A
MA
Raikhel
Natasha V
NV
Rojo
Enrique
E
D017360:Arabidopsis / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D037121:Plant Lectins / Q000378:metabolism; D021381:Protein Transport / Q000502:physiology; D050766:Qb-SNARE Proteins / Q000378:metabolism*; D014617:Vacuoles / Q000378:metabolism*
C118167:AT2G27250 protein, Arabidopsis; D029681:Arabidopsis Proteins; D037121:Plant Lectins; D050766:Qb-SNARE Proteins; C120751:vesicle transport v-SNARE 11 protein, Arabidopsis; C120752:vesicle transport v-SNARE 12 protein, Arabidopsis