Chloroplast biogenesis involves the coordinated expression of the plastid and nuclear genomes, requiring information to be sent from the nucleus to the developing chloroplasts and vice versa. Although it is well known how the nucleus controls chloroplast development, it is still poorly understood how the plastid communicates with the nucleus. Currently, haem is proposed as a plastid-to-nucleus (retrograde) signal that is involved in various physiological regulations, such as photosynthesis-associated nuclear genes expression and cell cycle in plants and algae. However, components that transduce haem-dependent signalling are still unidentified. In this study, by using haem-immobilized high-performance affinity beads, we performed proteomic analysis of haem-binding proteins from Arabidopsis thaliana and Cyanidioschyzon merolae. Most of the identified proteins were non-canonical haemoproteins localized in various organelles. Interestingly, half of the identified proteins were nucleus proteins, some of them have a similar function or localization in either or both organisms. Following biochemical analysis of selective proteins demonstrated haem binding. This study firstly demonstrates that nucleus proteins in plant and algae show haem-binding properties. This article is part of the theme issue 'Retrograde signalling from endosymbiotic organelles'.
Keywords: chloroplast; haem; nucleoproteins; proteomics; retrograde signal.