Fixed place
In the busy chloroplasts of a plant it is essential that starch has its own place to prevent it blocking the way. Now Swiss researchers show in PNAS that the protein MFP1 is picking the spot.
Starch is made by plants both to survive long and short periods or scarcity. While for the long terms scarcity starch is kept in specific organs, starch for short term scarcities stays in the chloroplasts. These glucose production centres are busy places. The production of temporary starch is therefore taking place at specific places. This, to prevent starch from blocking the way. But how the plant is deciding where to place its starch was still unknown.
To study this, the researchers turned to one of a group of recently discovered proteins that are involved in starch production, MFP1. In the group of recently discovered proteins involved in starch production MFP1 is a bit of an outsider. It is the only protein that is attached to the membrane. In this case to one of the membrane structures inside the chloroplasts.
MFP1 is the floor manager by starch production
The first thing the researchers did was analyse the influence of MFP1 on starch production. Less MFP1 resulted indeed in less starch. And more MFP1 in a little bit more starch granules.
But the interesting bit came when the researchers studied the influence of being attached toe the membrane. When they uncoupled MFP1 from the membrane, then the plant still produced starch granules, but less. When they gave MFP1 instructions to attach to a different chloroplast membrane, like its outer membrane, then the starch granules were only formed there.
MFP1 is therefore telling the rest of the starch production proteins where to set up shop. To make sure that the starch in the chloroplast is not blocking the way. Showing that even plants use floor managers to prevent the cell, or in this case the chloroplast, from turning it in an obstacle course from proteins.
Literature
Mayank Sharma, Melanie R. Abt, Simona Eicke , and Samuel C. Zeeman (2024) MFP1 defines the subchloroplast location of starch granule initiation. PNAS 121 (3) e2309666121, https://doi.org/10.1073/pnas.2309666121
Plant en Zo 