Phytochrome signalling modulates the SA‐perceptive pathway in Arabidopsis

Abstract

SummaryThe interaction of phytochrome signalling with the SA signal transduction pathway has been investigated in Arabidopsis using single and multiple mutants affected in light perception (phyA and phyB de®cient) and light-signal processing (psi2, phytochrome signalling). The induction of PR1 by SA and functional analogues has been found to strictly correlate with the activity of the signalling pathway controlled by both phyA and phyB photoreceptors. In darkness as well as dim light, and independently of a carbohydrate source, SA-induced PR gene expression as well as the hypersensitive response to pathogens (HR) are strongly reduced. Moreover, the initiation of HR also exhibits a strict dependence upon both the presence and the amplitude of a phytochrome-elicited signal. The growth of an incompatible strain of bacterial a pathogen (Pseudomonas syringae pv. tomato) was enhanced in phyAphyB and decreased in psi2 mutants. While functional chloroplasts were found necessary for the development of an HR, the induction of PRs was strictly dependent on light, but independent of functional chloroplasts. Taken together, these data demonstrate that the light-induced signalling pathway interacts with the pathogen/SA-mediated signal transduction route. These results are summarized in a formalism that allows qualitative computer simulation.

Light Regulation and Daytime Dependency of Inducible Plant Defenses in Arabidopsis: Phytochrome Signaling Controls Systemic Acquired Resistance Rather Than Local Defense

“…Light is the major external factor influencing plant growth and development, and an appropriate light environment is also required for the establishment of a complete set of resistance responses in several plant-pathogen interactions (Roberts and Paul, 2006). In tobacco (Nicotiana tabacum), rice (Oryza sativa), and Arabidopsis (Arabidopsis thaliana), HR-associated programmed cell death triggered by bacterial and viral pathogens is light dependent (Lozano and Sequeira, 1970;Guo et al, 1993;Genoud et al, 2002;Zeier et al, 2004;Chandra-Shekara et al, 2006). Similarly, the constitutive cell death phenotype of Arabidopsis acd11 and lsd1 mutants is only evident when light of a certain quantity or duration is present (Brodersen et al, 2002;Mateo et al, 2004).…”

“…Moreover, Arabidopsis plants inoculated in darkness with an avirulent strain of Pseudomonas syringae are not able to substantially accumulate the phenolic metabolite SA and fail to induce expression of the key phenylpropanoid pathway enzyme Phe ammonia lyase (PAL; Zeier et al, 2004). Light is not only required for SA biosynthesis, but also controls SA perception, because treatment of Arabidopsis leaves with exogenous SA in dim light or in the dark results in strongly reduced expression of the SA-induced defense gene PR-1 (Genoud et al, 2002). Both impaired production and perception of SA therefore account for the observation that PR-1 expression in P. syringae-treated Arabidopsis leaves is completely suppressed in darksituated plants (Zeier et al, 2004).…”

“…Thus, lightcontrolled activation of these responses can explain why resistance of plants to many bacterial and viral pathogens is attenuated in the dark (Lozano and Sequeira, 1970;Guo et al, 1993;Genoud et al, 2002;Zeier et al, 2004;Chandra-Shekara et al, 2006). It is noteworthy, however, that several inducible plant defenses occurring at sites of pathogen inoculation do not require the presence of light.…”

“…Whether and how specific light-induced signaling pathways interact with defense pathways has only scarcely been investigated. Genoud et al (2002) have demonstrated cross talk between phytochrome signaling and both SA perception and HR development in Arabidopsis upon inoculation with avirulent P. syringae. The lightdependent HR triggered by Turnip crinkle virus and resistance to viral infection, on the other hand, proved to be phytochrome independent (Chandra-Shekara et al, 2006).…”

Heterotrimeric G-protein is involved in phytochrome A-mediated cell death of Arabidopsis hypocotyls

“…Screening of mutants resistant to FR-induced killing in the absence of sucrose led to the isolation of a novel phy A signal-transduction gene (PAT1), which acts as an early signaling component in the cytoplasm [36]. In addition, the phyA signaling pathway has been demonstrated to function in the SA-induced hypersensitive response [37]. We therefore speculate that hypocotyls could also be used as a potential model system for the identification of important components in the phyA-mediated cell-death pathway when sugar is present in the growth media.…”