This project investigated the functions of proteins that control activation of plant immune responses that protect plants from disease caused by microbial pathogens such as the bacterium Pseudomonas syringae. The genome of the plant Arabidopsis thaliana contains a family of genes named CBP60 genes. These genes enocde proteins called transcription factors that function to control the activities of other genes. Three CBP60 genes are important in controlling immunity genes. They are CBP60a, CBP60g, and SARD1. 

CBP60g and SARD1 function to activate immunity genes, while CBP60a functions to repress them. By studying plants lacking one or more of these proteins, we found that negative control by CBP60a is important for returning the immune system to its resting state after a pathogen attack has ended. Using time course data and mathematical modeling, we found that lack of CBP60a protein did not increase the level of the immune response, but it did extend the length of the response. As immmune responses require energy, it is important for plants to avoid activation of immune responses when they are not required.

We also investigated the roles of two samll calcium-binding proteins called CML46 and CML47. At the beginning of the project, we thought that these proteins might modulate the activities of CBP60a or CBP60g. We did not find evidence of binding of CML46 or CML47 to CBP60a or CBP60g. However, we did find that CML46 and CML47 repress immune responses. Plants lacking these proteins showed stronger activation of immune responses when challenged by pathogens. CML46 and CML47 are part of the system that prevents excessive activation of immune responses.

Activation of plant immune responses involves a cascade of activation events including increases in the levels of transcription factors that in turn increase the levels of other immunity genes. The SARD1 gene is activated during immune responses, causing production of more SARD1 protein that in turn increases production of other proteins by activation of immunity genes. We investigated how activation of the SARD1 gene is controlled. We found that a protein called WRKY33 binds to the DNA of the SARD1 gene, preventing production of SARD1 protein in the absence of pathogens. In the absence of pathogens, lack of the WRKY33 protein results in increased production of SARD1 protein. In the presence of pathogens, lack of WRKY33 has no effect. Thus, activation of SARD1 likely involves removal of WRKY33 from the SARD1 gene.

The project providing scientific training to project participants. Two post-doctoral fellows worked on the project and gained technical skills and experience in experimental design and research project planning. A Ph.D. student studying computer science worked on the mathematical modeling of CBP60a function, gaining experience in interdisciplinary science. Two female undergraduate Honors students worked on the project and wrote about their work in Honors theses. These students are presently enrolled in Medical School. Another female student who is a first-generation immigrant worked on the project for several years. She has now graduated and is pursuing a research career.

Last Modified: 02/27/2020
Modified by: Jane Glazebrook