Tomato Plants: How Proteases Affect Photosynthesis and Fruit Ripening

Proteases are enzymes that break down proteins. In plants, some proteases are found in the chloroplasts, specifically in the thylakoid lumen. One family of these proteases is called Deg. Deg1, Deg5, and Deg8 are three members of this family that have been studied quite a bit. They are thought to help fix damaged photosystem II (PSII) complexes during photoinhibition. This is when light damages the plant's ability to photosynthesize. Researchers have been debating whether Deg5 and Deg8 are really needed for this repair process in a plant called Arabidopsis. This debate, along with curiosity about how chloroplast proteases work during the transition from chloroplasts to chromoplasts, led scientists to study these proteases in tomato plants. During this transition, the thylakoid network breaks down. To do this, scientists created tomato plants that lacked SlDeg1, SlDeg5, and SlDeg8. They then looked at how these plants performed photosynthesis and how their fruits developed and ripened. Plants without SlDeg1 had yellowish leaves and grew poorly. However, plants without both SlDeg5 and SlDeg8 looked and performed just like normal tomato plants. Their photosynthesis was not affected, even under different conditions. The fruits of these plants also developed and ripened normally, and the plants produced the same amount of fruit. This led the scientists to conclude that SlDeg5 and SlDeg8 are not necessary for photosynthesis or fruit ripening in tomato plants. This is a surprising finding, as it challenges the idea that these proteases are crucial for these processes. The study raises several questions. If SlDeg5 and SlDeg8 are not essential, what other roles might they play in the plant? Or, are there other proteases that can take over their functions? Understanding these questions could help us better understand how plants adapt to different conditions and how we can improve crop yields.