Dissecting cardosin B trafficking pathways in heterologous systems.
In cardoon pistils, while cardosin A is detected in the vacuoles of stigmatic papillae, cardosin B accumulates in the extracellular matrix of the transmitting tissue. Given cardosins' high homology and yet different cellular localisation, cardosins represent a potentially useful model to understand and study the structural and functional plasticity of plant secretory pathways. The vacuolar targeting of cardosin A was replicated in heterologous species so the targeting of cardosin B was examined in these systems. Inducible expression in transgenic Arabidopsis and transient expression in tobacco epidermal cells were used in parallel to study cardosin B intracellular trafficking and localisation. Cardosin B was successfully expressed in both systems where it accumulated mainly in the vacuole but it was also detected in the cell wall. The glycosylation pattern of cardosin B in these systems was in accordance with that observed in cardoon high-mannose-type glycans, suggesting that either the glycans are inaccessible to the Golgi processing enzymes due to cardosin B conformation or the protein leaves the Golgi in an early step before Golgi-modifying enzymes are able to modify the glycans. Concerning cardosin B trafficking pathway, it is transported through the Golgi in a RAB-D2a-dependent route, and is delivered to the vacuole via the prevacuolar compartment in a RAB-F2b-dependent pathway. Since cardosin B is secreted in cardoon pistils, its localisation in the vacuoles in cardoon ovary and in heterologous systems, suggests that the differential targeting of cardosins A and B in cardoon pistils results principally from differences in the cells in which these two proteins are expressed.
da Costa
Diana Soares
DS
Departamento de Biologia, Faculdade de Ciências da Universidade do Porto, Rua do Campo Alegre, s/nº, 4169-007, Porto, Portugal. diana.costa@fc.up.pt
Pereira
Susana
S
Moore
Ian
I
Pissarra
José
J
D017360:Arabidopsis / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D001692:Biological Transport; D030821:Plants, Genetically Modified
D029681:Arabidopsis Proteins