To begin photosynthesis, the plants send anterograde signals to themselves. The signal activates the plastid-encoded bacterial-type RNA polymerase (PEP) to transcribe plastid photosynthesis genes. However, the identity of the anterograde signal remains to be understood. The main challenge was to distinguish regulators from the abundance of necessary components for plastid transcription and other essential chloroplast functions, such as photosynthesis.

Scientists at UC Riverside have now decoded those previously opaque signals.

The core codes for hundreds of proteins that contain building blocks for the smaller organelles. The biggest challenge was to determine which ones are the signal for them to start photosynthesis.

Previously, scientists identified specific proteins in plant nuclei that are activated by light and initiate photosynthesis. In this study, scientists identified four proteins that are part of that reaction. These proteins send a signal that turns small organs into chloroplasts, which generate growth-promoting sugars.

UCR botany professor Meng Chen said: “The conductors of the symphony are proteins in the nucleus called photoreceptors that respond to light. We have shown in this paper that both red and blue photoreceptors initiate the symphony. They activate genes that code for the building blocks of photosynthesis.”

The specific circumstance in this case is that both local (the core) and outside musicians conduct the symphony in two separate “rooms” within the cell. As a result, the conductors (photoreceptors), which are only present in the core, have to transmit some messages to the musicians who are far away. The four recently identified proteins from the nucleus to the chloroplasts regulate this final stage.

Chen said, “Currently, a lot of research describes the communication of organelles back to the nucleus. If something is wrong with the organelles, they send signals to the “headquarters” of the nucleus. Much less is known about the activity-regulating signals sent from the nucleus to the organelles.”

“The nucleus may similarly control the expression of mitochondrial and chloroplast genes. So the principles we learn from the nucleus-to-chloroplast communication pathway may enhance our understanding of how the nucleus regulates mitochondrial genes and their dysfunction in cancer.”

“The importance of understanding how photosynthesis is controlled has applications beyond disease research. Human settlements on another planet likely require indoor farming and the creation of a lighting scheme to increase yields in that environment. In fact, climate change is putting growers on this planet for challenges.”

Magazine reference:

  1. Hwang, Y., Han, S., Yoo, C.Y. et al. Anterograde signaling regulates plastid transcription via sigma factors separately from nuclear photosynthesis genes. Nat Commun 13, 7440 (2022). DOI: 10.1038/s41467-022-35080-0