Humans rely on the arsenal of cells, molecules, and biochemical pathways of the immune system to defend the body when it's threatened by pathogens. But there are many different biological mechanisms that help shield cells from invaders, like the simple CRISPR system that bacteria use against viruses. Scientists have now revealed a defensive mechanism used by plant cells. Even though plant cells remain immobile within plants, those cells can transform to become PRimary IMmunE Responder (PRIMER) cells, a novel cell group that has immune functions in plants.
These PRIMER cells were found to be surrounded by other special cells known as bystander cells that appear to act as transmitters for the plant immune response. The findings have been reported in Nature.
"In nature, plants are constantly being attacked and require a well-functioning immune system," said senior study author Professor Joseph Ecker, the Salk International Council Chair in Genetics, and Howard Hughes Medical Institute investigator.
Plants can be threatened by bacteria or fungi, for example, which infect plant cells. The immobile, individual plant cells have to then react to the pathogen and alert neighboring cells.
Since this can play out in different ways, with various pathogens able to affect different parts of a plant at the same time, there may be various immune responses happening at any one time in different parts of the same plant. The situation can become complex.
In this study, the researchers exposed a common plant model called Arabidopsis thaliana to various pathogenic bacteria, then applied advanced techniques called single-cell multiomics and spatial transcriptomics. The combined techniques revealed the immune responses in individual plant cells by showing which genes were active, and where.
Study co-author Travis Lee of Salk and Howard Hughes Medical Institute discusses spatial transcriptomics techniques related to plant research in the video above.
PRIMER cells were found to be expressing a transcription factor, which affects the expression of other genes, called GT-3a. The bystander cells surrounding the PRIMERS were also found to promote long distance cell-to-cell signaling.
The spatiotemporal gene expression data is now also freely available online.
"There is a lot of interest and demand for detailed cell atlases these days, so we're excited to create a new one that is publicly available for other researchers to use," said Ecker. "Our atlas could lead to many new discoveries about how individual plant cells respond to environmental stressors, which will be crucial for creating more climate-resilient crops."
Sources: Salk Institute, Nature