Coordination of Plant Growth and Defense Through Key Regulators in Salicylic Acid and Brassinosteroid Pathways

University Of South Carolina At Columbia, Columbia SC

Investigators

Abstract

In their natural environments, plants can be infected by many pathogens including fungi, bacteria, oomycetes, viruses, and nematodes. Therefore, a robust immune system is a prerequisite for the survival of plants. Unfortunately, when plants allocate energy for defense instead of growth, there is a fitness cost, which will compromise plant growth, resulting crop yield loss. The plant defense hormone salicylic acid (SA) plays an essential role in plant defense against many pathogens. In contrast, the endogenous hormones called brassinosteroids (BRs) regulate multiple physiological processes required for normal plant growth and development. Plants have developed sophisticated strategies to coordinate growth and immunity, but our understanding of the underlying mechanisms remains limited. This project aims to unravel fundamental mechanisms of plant growth and defense coordination through interactions between key regulators in BR and SA pathways. These studies will greatly increase the understanding of how plants achieve balanced growth and defense at the molecular level and will ultimately contribute to the development of effective and novel strategies to control crop diseases without significant yield loss. Funding from this project will be used to train middle and high students and teachers on detecting citrus greening disease at early stages before the citrus trees show any obvious symptoms. By connecting molecular technology with urgent real-life problems, our program will showcase the importance of plant science and inspire students to become the next generation of leading plant scientists. Plants deploy a two-tiered surveillance system, which includes pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) and effector-triggered immunity (ETI), to recognize invading pathogens. After a local infection by a pathogen, plants can activate stronger and faster defense responses in the entire plant against later infections by a broad spectrum of pathogens. This phenomenon is termed systemic acquired resistance (SAR). Early studies have demonstrated that EDS1 and NPR1 function as two central hubs in SA-mediated plant defense, while BZR1 and BES1 act as two key transcription factors in the plant growth hormone BR signaling. This project focuses on investigating how plants optimize growth and defense through the crosstalk between BR and SA. The preliminary data have shown that both EDS1 and NPR1 interact with BES1, while EDS1 is also physically associated with BZR1. The published data demonstrated that SA, NPR1, and EDS1 inhibit hypocotyl elongation, while BZR1 regulates ETI. The first objective of this project is to study whether and how BZR1 and BES1 influence PTI through interacting with EDS1 and NPR1. The second objective is to determine if and how BZR1 and BES1 impact ETI and systemic plant immunity by affecting the functions of EDS1 and NPR1. The final objective is to elucidate the roles of EDS1 and NPR1 in SA-mediated plant growth inhibition through their physical associations with key regulators in the BR pathway. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.