Journal
JOURNAL OF EXPERIMENTAL BOTANY
Volume 64, Issue 6, Pages 1587-1601Publisher
OXFORD UNIV PRESS
DOI: 10.1093/jxb/ert014
Keywords
8S globulin; ER body; pre-vacuolar compartment; storage protein
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Funding
- Research Grants Council of Hong Kong [CUHK466309, CUHK466610, CUHK466011, CUHK465112, CUHK2/CRF/11G]
- NSFC/RGC [N_CUHK406/12]
- CUHK Schemes
- CAS-Croucher Funding Scheme
- German Research Council [Ro 440/11]
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This study investigated the subcellular location of mung bean (Vigna radiata) 8S globulin in transient expression systems as well as in tobacco (Nicotiana tabacum) BY-2 cells and different tissues from a transgenic Arabidopsis (Arabidopsis thaliana) line stably expressing this storage globulin. When transiently expressed in protoplasts from both BY-2 cells and Arabidopsis suspension cultured cells, the 8S globulin located to structures that were neither Golgi nor pre-vacuolar compartments (PVCs). Immunogold electron microscopy of the transgenics reveals the 8S globulin-positive structures to be small, spherical, ribosome-covered endoplasmic reticulum (ER)-derived bodies. In BY-2 cells and all vegetative cells, the 8S globulin was present as a pro-form. However, in Arabidopsis embryos, with the onset of endogenous storage protein synthesis, the 8S globulin exited the ER and passed through the PVC to the protein storage vacuole where it was processed to its smaller mature form. These results clearly demonstrated that, when taken out of context and expressed in vegetative cells, the mung bean 8S storage globulin cannot exit the ER, and indicate that natural targeting of storage proteins to the vacuole should be better studied in the maturing seed.
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