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Cyclic-nucleotide-gated ion channels (CNGCs) are nonselective cation channels that were first identified in vertebrate retinal photoreceptors and olfactory sensory neurons. The role of CNGCs in animals is well documented, and they are believed to localize to the plasma membrane as heterotetramers. So far, only six CNGC genes (CNGA1-4, CNGB1, and CNGB3) have been identified in mammalian genomes. In contrast, the Arabidopsis thaliana (L.) Heynh. genome encodes 20 putative CNGC subunits that are thought to assemble in the same tetrameric form as animal subunits do. Although the study of Arabidopsis CNGCs is still in its infancy, current research revealed their ability to transport cations that play a role in mediating various biotic and abiotic stresses and developmental processes. This review discusses the current knowledge of plant CNGCs and focuses on functional aspects, with references to heterologous expression studies and reverse genetics analyses. In addition, structural aspects of these channels are discussed. Les canaux ioniques controles par des nucleotides cycliques (CNGCs) constituent des canaux cationiques non selectifs identifies pour la premiere fois dans les neurones sensitifs des photorecepteurs de la retine et de l'olfaction chez les vertebres. On dispose d'une bonne documentation sur le role des CNGCs chez les animaux, et on croit qu'ils sont localises sur la membrane plasmique comme heterotetrameres. Jusqu'ici on a identifie seulement six genes des CNGCs (CNGCA1-4, CNGCB1 et 3) dans des genomes animaux. Au contraire, le genome de l'Arabidopsis thaliana code pour 20 presumees sous-unites de CNGC, que l'on croit s'assembler sous la meme forme que les sous-unites animales le font. Bien que l'etude des CNGCs de l'Arabidopsis soit a ses debuts, la recherche en cours revele leur capacite a transporter les cations jouant un role en intervenant dans divers stress biotiques et abiotiques ainsi que des processus developpementaux. Dans cette revue, les auteurs discutent des connaissances actuelles sur les CNGCs des plantes et mettent l'accent sur les aspects fonctionnels, en relation avec des etudes d'expression heterologues et des analyses genetiques inversees. On discute de plus les aspects structuraux de ces canaux. [Traduit par la Redaction], Physiological roles of cyclic-nucleotide monophosphates (cNMPs) All organisms utilize networks of signaling pathways to elicit a plethora of biological responses involving developmental processes, abiotic and biotic stress responses, nutrient acquisition, [...]

Plants launch a concerted immune response to dampen potential infections upon sensing microbial pathogen and insect invasions. The transient and rapid elevation of the cytosolic calcium concentration [Ca2+]cyt is among the essential early cellular responses in plant immunity. The free Ca2+ concentration in the apoplast is far higher than that in the resting cytoplasm. Thus, the precise regulation of calcium channel activities upon infection is the key for an immediate and dynamic Ca2+ influx to trigger downstream signaling. Specific Ca2+ signatures in different branches of the plant immune system vary in timing, amplitude, duration, kinetics, and sources of Ca2+. Recent breakthroughs in the studies of diverse groups of classical calcium channels highlight the instrumental role of Ca2+ homeostasis in plant immunity and cell survival. Additionally, the identification of some immune receptors as noncanonical Ca2+-permeable channels opens a new view of how immune receptors initiate cell death and signaling. This review aims to provide an overview of different Ca2+-conducting channels in plant immunity and highlight their molecular and genetic mode-of-actions in facilitating immune signaling. We also discuss the regulatory mechanisms that control the stability and activity of these channels. [ABSTRACT FROM AUTHOR]

Transgenic tobacco deficient in the [H.sub.2]-[O.sub.2]-removing enzyme catalase (Cat1AS) was used as an inducible and noninvasive system to study the role of [H.sub.2][O.sub.2] as an activator of pathogenesis-related (PR) proteins in plants. Excess [H.sub.2][O.sub.2] in Cat1AS plants was generated by simply increasing light intensities. Sustained exposure of Cat1AS plants to excess [H.sub.2][O.sub.2] provoked tissue damage, stimulated salicylic acid and ethylene production, and induced the expression of acidic and basic PR proteins with a timing and magnitude similar to the hypersensitive response against pathogens. Salicylic acid production was biphasic, and the first peak of salicylic acid as well as the peak of ethylene occurred within the first hours of high light, which is long before the development of tissue necrosis. Under these conditions, accumulation of acidic PR proteins was also seen in upper leaves that were not exposed to high light, indicating systemic induction of expression. Short exposure of Cat1AS plants to excess [H.sub.2][O.sub.2] did not cause damage, induced local expression of acidic and basic PR proteins, and enhanced pathogen tolerance. However, the timing and magnitude of PR protein induction was in this case more similar to that in upper uninfected leaves than to that in hypersensitive-response leaves of pathogen-infected plants. Together, these data demonstrate that sublethal levels of [H.sub.2][O.sub.2] activate expression of acidic and basic PR proteins and lead to enhanced pathogen tolerance. However, rapid and strong activation of PR protein expression, as seen during the hypersensitive response, occurs only when excess [H.sub.2][O.sub.2] is accompanied by leaf necrosis.