Subcellular localization of Arabidopsis thaliana heme-binding protein 1 (AtHBP1), AtHBP2 and AtHBP3

Heme is an essential pigment in various biochemical processes in plant cells, including oxidoreduction and electron transport. Plastids are known to be the site of heme synthesis in plant cells while the transport mechanism of heme from plastids to apoproteins that require heme in the cytosol and various organelles is still enigmatic. AtHBP1, AtHBP2, and AtHBP3, members of the SOUL/p22 heme binding protein family in Arabidopsis thaliana, are regarded as candidate cytosolic heme carrier proteins. However, the subcellular localization of the AtHBPs has not been determined. In this study, we investigated transcription levels and subcellular localization of the AtHBPs. Semi-quantitative RT-PCR analysis revealed that AtHBP1, AtHBP2 and AtHBP3 were transcribed in various tissues. The transcription levels of AtHBP1 and AtHBP3 in roots were lower than in other tissues. To reveal the subcellular localization of AtHBP1, AtHBP2 and AtHBP3, we constructed transgenic A. thaliana lines expressing Venus fluorescent protein fused, respectively, to the C-terminus of AtHBP1, AtHBP2 and AtHBP3. AtHBP1::Venus accumulated around the nucleus, AtHBP2::Venus was detected in the cytosol, and AtHBP3::Venus was observed in the peripheral region of the cell.