The Arabidopsis Gene CAD1 Controls Programmed Cell Death in the Plant Immune System and Encodes a Protein Containing a MACPF Domain

Abstract

To clarify the processes involved in plant immunity, we have isolated and characterized a single recessive Arabidopsis mutant, cad1 (constitutively activated cell death 1), which shows a phenotype that mimics the lesions seen in the hypersensitive response (HR). This mutant shows spontaneously activated expression of pathogenesis-related (PR) genes, and leading to a 32-fold increase in salicylic acid (SA). Inoculation of cad1 mutant plants with Pseudomonas syringae pv tomato DC3000 shows that the cad1 mutation results in the restriction of bacterial growth. Cloning of CAD1 reveals that this gene encodes a protein containing a domain with significant homology to the MACPF (membrane attack complex and perforin) domain of complement components and perforin proteins that are involved in innate immunity in animals. Furthermore, cell death is suppressed in transgenic cad1 plants expressing nahG, which encodes an SA-degrading enzyme. We therefore conclude that the CAD1 protein negatively controls the SA-mediated pathway of programmed cell death in plant immunity.

Salicylic Acid and a Chitin Elicitor Both Control Expression of theCAD1Gene Involved in the Plant Immunity ofArabidopsis

“…10) In this study, we found that the CAD1 gene is under the control of SA and a chitin elicitor. Gathering all lines of evidence together, we propose the following model of transcriptional regulation of the CAD1 gene in plant immunity (Fig.…”

“…The CAD1 gene is up-regulated by SA A previous study 10) indicates that the CAD1 protein negatively controls the SA-mediated pathway of programmed cell death in plant immunity. We examined the expression pattern of the CAD1 gene in this study.…”

“…10) The MACPF domain of CAD1 is closely related to those of the C6-C9 components of the mammalian complement system. Complement provides a critical and multifaceted defense system against infection.…”

“…10) Chitin, a polysaccharide composed of -1!4-linked N-acetyl-D-glucosamine, is a structural element found in fungal cell walls, insect exoskeletons, and the hard carapace of crustaceans. Increasing evidence indicates that chitin and chitin oligomers can regulate defensive, symbiotic, and developmental processes in plants.…”

Overexpression of Arabidopsis ACBP3 Enhances NPR1-Dependent Plant Resistance to Pseudomonas syringe pv tomato DC3000

“…SA was extracted from 0.3 to 0.5 g of 4-week-old leaves of wild-type, ACBP3-OE, and ACBP3-KO plants according to Morita-Yamamuro et al (2005). After extraction, the dried residues were resuspended in 50% methanol and analyzed by HPLC with a fluorescent detector set at excitation = 295 nm and emission = 370 nm.…”