Battle Tactics: Ralstonia Solanacearum K60 Type III Effector Impacts Plant Cytoskeleton
Abstract
Unlike mammals, plants lack an adaptive immune system and rely solely on innate immunity to recognize microbial pathogens. To further defend against pathogens, plants evolved two layers of immune systems to recognize and fend off pathogens. The first branch, PAMPs-Triggered Immunity (PTI), relies on cell-surface localized and intracellular receptors (pathogen recognition receptors; PRRs) to recognize PAMPs (pathogenic associated molecular patterns). This recognition activates several immune outputs, such as calcium influx, reactive oxygen species (ROS), and callose deposition. In a second layer, plants can launch a more specific and robust immune response called ETI (Effector Triggered Immunity). To counter plant immunity, bacterial pathogens deliver virulence proteins, known as T3Es (type III effectors), into plant cells through a needle-like apparatus called the type III secretion system (T3SS). To perform their functions, T3E localizes to different subcellular compartments to affect host cell functionality; therefore, knowing T3E localization is informative for developing hypotheses about effectors and their potential targets. Thus, to gain insight into the function of Ralstonia T3Es, we examined the in planta localization of 19 T3Es from Ralstonia species. This localization screening revealed a novel T3E that localizes to the host cytoskeleton. The plant cytoskeleton is commonly considered a vital component of cell growth and development; however, it also plays a critical role in plant immunity. During plant immunity, the cytoskeleton orchestrates rapid and precise immune-associated processes. For instance, the cytoskeleton mobilizes and orients the movement of organelles, proteins, and chemical signaling. Currently, only eight documented bacterial T3Es impact the cytoskeleton: four from Pseudomonas syringae (HopW1, HopG1, HopZa1, HopE1), three from Xanthomonas spp. (XopR, AvrBsT, and XopL) and one from Acidovorax citrulli (AopW1). A novel T3E, called RipU, interacts with the cytoskeleton. Data has shown that RipU co-localizes with cytoskeletal markers in tobacco leaves. Ectopic expression of RipU can suppress PTI responses like ROS bursts or seedling growth inhibition. Tomato plants inoculated with Rs K60 lacking RipU showed less wilting and root colonization, suggesting that RipU plays a role in pathogenesis and virulence. Furthermore, inducible expression of RipU in Arabidopsis dramatically alters plant development. These plants have wavy roots, branching root hairs, and underdeveloped true leaves. Our results suggest that by targeting the cytoskeleton, RipU contributes to Rs K60s pathogenicity and virulence.
Degree
Ph.D.
Advisors
Iyer-Pascuzzi, Purdue University.
Subject Area
Agronomy|Cellular biology|Genetics
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.