Similar yet different: A leaf photosynthetic cell type reveals its unique molecular blueprint

Procko et al. investigate the molecular identities of specialized photosynthetic cell types in leaves.

By Carl Procko and Travis Lee.

Salk Institute for Biological Studies, CA

Background: Photosynthesis is arguably the most important biochemical process in plants, and provides humans and other animals with food and oxygen. This process generally occurs in specialized cell types in the leaf. One type of photosynthetic cell, called palisade, forms one or more cell layers at the top of the leaf in many plant species. Despite the importance of these cells, we know surprisingly little at the molecular level as to how palisade differs from other photosynthetic cell types.

Question: We wanted to compare the gene expression profile of palisade cells to other photosynthetic cell types to discover their unique roles in leaf biology. We did this by using a combined approach of bulk palisade cell purification and single cell analysis in the model plant Arabidopsis thaliana.

Findings: Despite their unique morphology and placement in the leaf, gene expression was similar between the palisade and other photosynthetic cell types. Nevertheless, our complementary approaches revealed a role for the palisade in production of a UV light absorbing molecule called sinapoylmalate, which acts as a “sunscreen” to reduce the damaging effects of UV light. This may serve to protect the palisade and/or additional cell types in the leaf. These results provide a better understanding of how different leaf cells function to optimize overall leaf performance.

Next steps: In the course of our studies we generated novel genetic tools to probe the function of the palisade and other photosynthetic cells. Future cell-specific manipulations using these tools will further explore how these cells contribute to leaf function across different environments. This will provide insights into why and how leaves adopt different cellular architectures.

Carl Procko, Travis Lee, Aleca Borsuk, Bastiaan O. R. Bargmann, Tsegaye Dabi, Joseph R. Nery, Mark Estelle, Lisa Baird, Carolyn O’Connor, Craig Brodersen, Joseph R. Ecker, Joanne Chory. (2022). Leaf cell-specific and single-cell transcriptional profiling reveals a role for the palisade layer in UV light protection.