BBSRC-NSF/BIO: Anatomy and Functions of LTP Interactomes and Their Relationship to Small RNA Signals in Systemic Acquired Resistance

Abstract Plants, like all living organisms constantly combat pathogenic microbes. Their sessile nature and lack of an active circulatory system pose particular problems. To ensure survival, plants have evolved unique defense mechanisms including the induction of systemic defense responses such as systemic acquired resistance (SAR). SAR is a highly desirable because it protects plants against a broad-spectrum of pathogens and is unique because it generates a “memory” of pathogen infection to provide broad-spectrum protection against pathogens unrelated to the primary agent. Furthermore, this broad- spectrum immunity can be passed on to neighboring individuals and immediate progeny. Because of its unique mechanistic properties and potential to contribute to Food Security, SAR has received renewed interest from plant biologists. The processes to be studied in this project are fundamental to our understanding of plant immunity. Host resistance to pathogens is genetically accessible and this environmentally friendly approach continues to be widely used in crop breeding. By elucidating the mechanisms through which plants establish, systemic immunity will offer new strategies and opportunities for engineering broad spectrum resistance in crop species. SAR involves the generation of mobile signals in the primary infected leaves, which when translocated to distal tissue activate defense responses resulting in disease resistance. The production of the mobile signal is thought to occur within 3 h of primary infection, and the infected leaf must remain attached for at least 4 h after inoculation for SAR to be induced, suggesting that the immunizing signal(s) is rapidly translocated. Many SAR inducing factors have been discovered of which salicylic acid (SA), azelaic acid (AzA) and glycerol-3-phosphate (G3P) function in a bifurcate pathway and are amongst the systemically transported SAR inducers, with AzA and G3P functioning in one branch and SA in the other. Recent analysis has shown that another SAR inducer pipecolic acid (Pip), functions upstream of the AzA-G3P branch and induces free radical accumulation. Systemic transport of both SA and G3P is essential for Pip accumulation in the uninfected distal tissue, and SAR induction. Although several SAR-inducing and systemically mobile signals have been identified, the identity of the early mobile signal (translocated within 6 h of primary infection) remains elusive. This project will utilize the combined expertise of the PIs at the University of Kentucky and University of Warwick to determine the mechanisms underlying transport of a recently discovered early mobile signal that is highly conserved and activates systemic immunity in diverse plants. The proposed research will also study the SAR related mode of action of this new mobile signal and its relationship to other SAR associated factors.