Genetic Elucidation of Nitric Oxide Signaling in Incompatible Plant-Pathogen Interactions

Abstract

Recent experiments indicate that nitric oxide (NO) plays a pivotal role in disease resistance and several other physiological processes in plants. However, most of the current information about the function of NO in plants is based on pharmacological studies, and additional approaches are therefore required to ascertain the role of NO as an important signaling molecule in plants. We have expressed a bacterial nitric oxide dioxygenase (NOD) in Arabidopsis plants and/or avirulent Pseudomonas syringae pv tomato to study incompatible plant-pathogen interactions impaired in NO signaling. NOD expression in transgenic Arabidopsis resulted in decreased NO levels in planta and attenuated a pathogen-induced NO burst. Moreover, NOD expression in plant cells had very similar effects on plant defenses compared to NOD expression in avirulent Pseudomonas. The defense responses most affected by NO reduction during the incompatible interaction were decreased H 2 O 2 levels during the oxidative burst and a blockage of Phe ammonia lyase expression, the key enzyme in the general phenylpropanoid pathway. Expression of the NOD furthermore blocked UV light-induced Phe ammonia lyase and chalcone synthase gene expression, indicating a general signaling function of NO in the activation of the phenylpropanoid pathway. NO possibly functions in incompatible plant-pathogen interactions by inhibiting the plant antioxidative machinery, and thereby ensuring locally prolonged H 2 O 2 levels. Additionally, albeit to a lesser extent, we observed decreases in salicylic acid production, a diminished development of hypersensitive cell death, and a delay in pathogenesis-related protein 1 expression during these NO-deficient plant-pathogen interactions. Therefore, this genetic approach confirms that NO is an important regulatory component in the signaling network of plant defense responses.Plants have evolved several mechanisms to defend themselves from bacterial or fungal invasion. The rapid recognition of pathogenic microbes is based on the interaction of products from a pathogen-derived avirulence gene and a plant-derived resistance gene and represents a prerequisite to specific resistance in incompatible plant-pathogen interactions (Flor, 1956). The multicomponent defense responses associated with specific resistance include a burst of reactive oxygen intermediates (ROI; Lamb and Dixon, 1997), transcriptional activation of defense genes encoding phenylpropanoid pathway enzymes, lytic and antimicrobial pathogenesis-related (PR) proteins (Lamb et al., 1989), increase of intracellular levels of salicylic acid (SA; Malamy et al., 1990; Métraux et al., 1990), and development of the hypersensitive response (HR). The HR results in the rapid appearance of a dry, necrotic lesion at the infection site that is clearly delimited from surrounding healthy tissue and is thought to contribute to the limitation of pathogen spread (Keen, 1990).One of the earliest events following pathogen recognition is a burst of oxidative metabolism leading to the generation of su...

Retracted: Nitric oxide enhances plant ultraviolet‐B protection up‐regulating gene expression of the phenylpropanoid biosynthetic pathway

“…However, UV-B-induced CHI expression was To confirm the relevance of NO in plant responses to UV-B He et al 2005;Tossi et al 2009), the role of endogenous NO in the UV-B response was deeply studied. As cPTIO becomes toxic for longterm assays, an Arabidopsis transgenic line expressing a bacterial NOD under the control of a DEX-inducible promoter was used (Zeier et al 2004). NOD expression in Arabidopsis results in decreased endogenous NO levels (Zeier et al 2004).…”

“…As cPTIO becomes toxic for longterm assays, an Arabidopsis transgenic line expressing a bacterial NOD under the control of a DEX-inducible promoter was used (Zeier et al 2004). NOD expression in Arabidopsis results in decreased endogenous NO levels (Zeier et al 2004).…”

“…By example in Lhasa (Tibet), the high-altitude area of the world, the overall maximum value for the UV-B intensity was 3.96 W m -2 during 1999-2003 (Norsang et al 2009). In King George Island (sea level, Antarctica) was 2.4 W m -2 during 2004(Zacher et al 2007). Both UV-B intensities are in the order of the UV-B doses used in this work.…”

“…NOD Arabidopsis plants express the bacterial flavohemoglobin Hmp background] generated by Agrobacterium-mediated plant transformation using the dexamethasone (DEX)-inducible expression vector pTA7001 as described in Zeier et al (2004). EV plants are control plants transformed with the pTA7001 EV.…”

A novel zinc‐binding alcohol dehydrogenase 2 from Arachis diogoi, expressed in resistance responses against late leaf spot pathogen, induces cell death when transexpressed in tobacco

“…Several lines of evidence have shown that the early nitric oxide (NO) burst in host plant cells after pathogen attack functions as a major defense response associated with resistance in plant pathogen interaction 55. NO is an interesting molecule that is used by microorganisms in pathogenesis and host cells to activate the immune system to counter the pathogen challenge 56, 57. Thus, the significant upregulation of AdZADH2 by the resistant host against the LLS pathogen attack under SNP treatment could be justified as a resistance response.…”