Chloroplasts are those little plant and algal cell structures whose primary function is to collect light. But if the plant is attacked by a pathogen, chloroplasts cease making food out of the sunlight they collect and rush to the part of the plant that is under attack. They do this to help the plant fend off the pesky invaders.
Scientists knew that chloroplasts do this, but they have only now figured out what forces them to act in this way. There is a protein that forces the organelles into action. This was discovered by pathologists from the Imperial College London when they infected a tobacco relative with a pathogen of the Irish potato famine. What they found is that the chloroplasts were called to defend the plant by a protein known as chloroplast unusual positioning 1 or CHUP1 for short. The protein’s primary function is to move chloroplasts to the part of the plant where the light enters it.
During the experiment, the scientists found a way to disable the CHUP1 gene, and due to this the chloroplasts were either slow to respond to an infection, or they ignored it completely. When CHUP1 was active, the chloroplasts stopped the process of photosynthesis and went to the site of the attack immediately to help defend the plant. The chloroplasts then wrapped around the microbe’s appendages, called haustoria, and released toxic by-products left behind from photosynthesis. This was all reported in a study published on January 9th of this year.
This reaction surprised scientists. They were not expecting the chloroplast to revert to behavior from a period when it was a free-living microbe. The researchers believe that they were photosynthetic bacterium at one point in their evolution and there is a high chance that this behavior was part of some primitive defense system which plants adopted at one point in their history to strengthen their immunity.