AUTHOR=Shanmugabalaji Venkatasalam , Grimm Bernhard , Kessler Felix 

TITLE=Characterization of a Plastoglobule-Localized SOUL4 Heme-Binding Protein in Arabidopsis thaliana

JOURNAL=Frontiers in Plant Science

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2020.00002

DOI=10.3389/fpls.2020.00002

ISSN=1664-462X

ABSTRACT=<p>Heme plays an active role in primary plant metabolic pathways as well as in stress signaling. In this study, we characterized the predicted heme-binding protein SOUL4. Proteomics evidence suggests that SOUL4 is a component of <italic>Arabidopsis</italic> plastoglobules (PGs, chloroplast lipid droplets). SOUL4 contains heme-binding motifs and the recombinant protein is shown here to bind heme <italic>in vitro</italic>. Fluorescence-tagged SOUL4 colocalized with the specific PG marker Fibrillin1A (FBN1A) in transiently transformed <italic>Nicotiana benthamiana</italic> leaves. In addition, SOUL4 cofractionated with another PG marker Fibrillin2 (FBN2) in sucrose gradient ultracentrifugation experiments. <italic>In vitro</italic> kinase experiments revealed that SOUL4 is phosphorylated by a yet unknown chloroplast protein kinase. Our data demonstrate that SOUL4 is a <italic>bona fide</italic> PG protein and may function in heme-buffering in the chloroplast.</p>