Chloroplast rich leaf
© iStock/coldsnowstorm

Researchers from the United Kingdom and Japan have discovered new details of how young leaves build their first chloroplast, identifying a new role of a previously uncharacterised protein.

At the point of germination from a seed, the plant begins to grow its first leaves, the race to build chloroplasts and survive begins. Without chloroplasts converting sunlight into energy, the light burns the plant from the inside out by producing harmful chemicals called reactive oxygen species.

Building the chloroplast requires a relay of communication signals between the developing chloroplasts and the plant cell’s central DNA centre, the nucleus. The protein characterised by researchers is call GUN1, which was known to have an important role in the communication between the chloroplast and the nucleus.

“GUN1 has been a mystery for such a long time,” said Professor Tatsuru Masuda from the University of Tokyo, leader of the ongoing research and final author of the recent publication in the Proceedings of the National Academy of Sciences.

GUN1 was previously difficult to study the protein is quickly degraded under sunlight. Researchers revealed that GUN1 influences the production and release of another communication molecule. During the first day of leaf development, GUN1 binds to an iron-containing molecule, famously used in meat alternatives, plant heme.

In a series of experiments using GUN1 isolated from young plant leaves, researchers observed the protein binding directly to heme and other tetraphyrroles, controlling the cell’s production of heme.

“We propose that GUN1 binds to heme to block it from moving from the chloroplast to the nucleus, which may help ensure that chloroplasts develop efficiently,” said Masuda

Due to GUN1 degrading in the presence of sunlight, it only releases heme to send signals to the nucleus while there is light available for the chloroplasts to photosynthesise into energy.

“Understanding how chloroplasts are built naturally may one day allow us to potentially manipulate how plants perform photosynthesis in unfavourable conditions, like under very high- or very low-intensity light,” said Masuda.

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