Abstract
A previous study demonstrated that two stromal proteins, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and glutamine synthetase, were released from chloroplasts into specific bodies, named Rubisco-containing bodies (RCBs), in wheat leaves. In this study, we visualized RCBs in living cells of transgenic Arabidopsis plants expressing stroma-targeted fluorescent proteins, and examined the involvement of autophagy on the accumulation and degradation of RCBs. In starved leaves treated with concanamycin A, we observed spherical bodies exhibiting GFP or DsRed fluorescence and Brownian movement in the vacuole but no chlorophyll fluorescence. Immuno-EM double-labeled with antibodies against RBCL and GFP confirmed that these fluorescent bodies correspond to RCBs. RCBs were not observed in leaves of atg mutant (Atatg5-1). In addition, stroma-targeted DsRed was co-localized with GFP-ATG8, which can be used as a marker for autophagosome, in spherical bodies found in the vacuole. These results indicate that stromal proteins can be degraded by ATG-dependent autophagic process under starved conditions.
