The involvement of Arabidopsis calmodulin in plant immunity against Pseudomonas syringae

Authors

Katherine Lagerstrom, University of Nebraska Lincoln

Date of this Version

Spring 2017

Document Type

Article

Citation

Environmental Studies Undergraduate Student Thesis, University of Nebraska–Lincoln, 2017

Comments

Copyright © 2017 Katherine Lagerstrom

Abstract

Calmodulin (CaM) is a calcium-binding protein present in all eukaryotic cells and is essential for many cellular functions. Calcium-specific binding to CaM induces a conformational change in CaM that affects its interaction with different target proteins, influencing the activity of proteins that bind it. Through calcium signal transduction, CaM mediates a variety of important cellular processes, including plant immunity. The Arabidopsis genome encodes 7 CaM genes that are highly conserved and homologous. While the involvement of CaMs in several eukaryotic processes is known, many of their biological functions in Arabidopsis remain largely unknown. Pseudomonas syringae pv. tomato DC3000 is pathogenic on tomato and Arabidopsis. It uses a type III secretion system to inject effector proteins into plant cells to favor pathogenicity. A major role of these type III effectors is to suppress plant immunity. It was recently found that one P. syringae effector (HopE1) utilizes CaM as a co-factor inside plant cells to target MAP65-1 and dissociate it from the microtubule network, thus inhibiting the secretion of important immune-related proteins. The main goal of this investigation was to examine Arabidopsis CaMs in order to identify those that may play a larger role in plant immunity to P. syringae. Arabidopsis mutated for each of the seven CAM genes were screened with a series of immunity assays and the expression levels of the CAM genes in wild type Arabidopsis in response to immunity activators were measured. Here, it was shown that cam4 and cam5 mutants, and cam1cam4 and cam2cam5 double mutants, were more resistant to infection by P. syringae. Additionally, it was shown that the expression levels of CAM1, CAM2, CAM3, and CAM5 were induced in wild type Arabidopsis upon activation of PTI and ETI.