Systemic Acquired Resistance

Abstract

Systemic acquired resistance (SAR) is a mechanism of induced defense that confers long-lasting protection against a broad spectrum of microorganisms. SAR requires the signal molecule salicylic acid (SA) and is associated with accumulation of pathogenesis-related proteins, which are thought to contribute to resistance. Much progress has been made recently in elucidating the mechanism of SAR. Using the model plant Arabidopsis, it was discovered that the isochorismate pathway is the major source of SA during SAR. In response to SA, the positive regulator protein NPR1 moves to the nucleus where it interacts with TGA transcription factors to induce defense gene expression, thus activating SAR. Exciting new data suggest that the mobile signal for SAR might be a lipid molecule. We discuss the molecular and genetic data that have contributed to our understanding of SAR and present a model describing the sequence of events leading from initial infection to the induction of defense genes.

OsWRKY03, a rice transcriptional activator that functions in defense signaling pathway upstream of OsNPR1

“…It has been suggested that disease resistance is associated with fitness costs and that plants have evolved inducible defense mechanism because it is too costly to have defense responses switch on all the time [5,75]. For instance, overexpression of AtWRKY6, AtWRKY18, AtWRKY53 or AtWRKY70 always resulted in small stunted transgenic plants [50,54,76].…”

“…ZB8 is a rice PAL gene and has been shown to be induced under wounding and fungal cell wall elicitor treatment [71]. Peroxidase genes are also a class of protective genes that are induced in plant defense response [5]. One rice peroxidase gene, POX22.3 has been shown to be predominantly induced upon X. oryzae pv.…”

“…Typical SAR results in an increment of endogenous SA and transcriptional activation of pathogenesis-related (PR) genes (e.g., PR1, PR2, PR5) [5]. It finally leads to an enhanced resistance to a broad spectrum of pathogens in distant and uninfected plant parts [6][7][8][9].…”

Plant defense response against Fusarium oxysporum and strategies to develop tolerant genotypes in banana

“…ROS along with NO (nitric oxide) induce HR (hypersensitive response)-mediated cell death (Delledonne et al 2001). ROS in association with salicylic acid are proposed to mediate the establishment of systemic defenses (Durrant and Dong 2004). The cytological studies have revealed that ROS and NO are associated with cell death adjacent to infected cells and so that both signals modulate each other's accumulation (Tada et al 2004).…”

Molecular cloning of a coiled-coil-nucleotide-binding-site-leucine-rich repeat gene from pearl millet and its expression pattern in response to the downy mildew pathogen

“…The R-proteins mediate a defense reaction culminating in hypersensitive response (HR) and eventually a localized cell death at the site of infection [1,2]. Further, the pathogenesis-related (PR) genes are induced in the host plant accelerating a systemic disease resistance against the pathogens throughout the plant [5].…”