Metabolite trafficking between organelles is widespread, yet many trafficking routes remain poorly understood. Biliverdin (BV), a tetrapyrrolic pigment, is involved in redox and light signaling in animal and plant cells. To visualize the inter-organelle trafficking of BV in living cells, we used smURFP, a BV-induced far-red fluorescent protein typically used for deep-tissue imaging in animals. Upon targeting of smURFP to various organelles in plant cells, we detected fluorescence from BV-bound smURFP in plastids and peroxisomes. Enhanced BV biosynthesis in plastids led to greater smURFP fluorescence in peroxisomes, and vice versa, indicating bidirectional trafficking of BV between these organelles. We also observed trafficking of BV between the cytosol and both plastids and peroxisomes, suggesting that bidirectional trafficking of BV between plastids and peroxisomes occurs via the cytosol. These findings provide a dynamic model for organelle-level metabolite trafficking.
Shibata et al. (Tue,) studied this question.