Previously, effect of Al ions on calcium signaling was assessed in tobacco cells expressing a Ca ... more Previously, effect of Al ions on calcium signaling was assessed in tobacco cells expressing a Ca 2+-monitoring luminescent protein, aequorin and a newly isolated putative plant Ca 2+ channel protein from Arabidopsis thaliana, AtTPC1 (two-pore channel 1). TPC1 channels were shown to be the only channel known to be sensitive to Al and they are responsive to reactive oxygen species and cryptogein, a fungal elicitor protein. Thus, involvement of TPC1 channels in calcium signaling leading to development of plant defense mechanism has been suggested. Then, the use of Al as a specific inhibitor of TPC1-type plant calcium channels has been proposed. Here, using transgenic tobacco BY-2 cells expressing aequorin, we report on the evidence in support of the involvement of Al-sensitive signaling pathway requiring TPC1-type channel-dependent Ca 2+ influx in response to salicylic acid, a key plant defense-inducing agent, but not to an elicitor prepared from the cell wall of rice blast disease fungus Magnaporthe grisea. In addition , involvement of Al-sensitive Ca 2+ channels in response to cold shock was also tested. The data suggested that the elicitor used here induces the Ca 2+ influx via Al-insensitive path, while salicylic acid and cold-shock-stimulate the influx of Ca 2+ via Al-sensitive mechanism.
Systemic acquired resistance (SAR), a natural disease response in plants, can be induced chemical... more Systemic acquired resistance (SAR), a natural disease response in plants, can be induced chemically. Salicylic acid (SA) acts as a key endogenous signaling molecule that mediates SAR in dicotyledonous plants. However, the role of SA in monocotyledonous plants has yet to be elucidated. In this study, the mode of action of the agrochemical protectant chemical probenazole was assessed by microarray-based determination of gene expression. Cloning and characterization of the most highly activated probenazole-responsive gene revealed that it encodes UDP-glucose:SA glucosyltransferase (OsSGT1), which catalyzes the conversion of free SA into SA O-b-glucoside (SAG). We found that SAG accumulated in rice leaf tissue following treatment with probenazole or 2,6-dichloroisonicotinic acid. A putative OsSGT1 gene from the rice cultivar Akitakomachi was cloned and the gene product expressed in Escherichia coli was characterized, and the results suggested that probenazole-responsive OsSGT1 is involved in the production of SAG. Furthermore, RNAi-mediated silencing of the OsSGT1 gene significantly reduced the probenazole-dependent development of resistance against blast disease, further supporting the suggestion that OsSGT1 is a key mediator of development of chemically induced disease resistance. The OsSGT1 gene may contribute to the SA signaling mechanism by inducing up-regulation of SAG in rice plants.
Indole-3-acetic acid (IAA) is the major natural auxin involved in regulation of a variety of grow... more Indole-3-acetic acid (IAA) is the major natural auxin involved in regulation of a variety of growth and developmental processes such as division, elongation and polarity determination in growing plant cells. It has been shown that dividing and/or elongating plant cells accompanies the generation of reactive oxygen species (ROS) and a number of reports have suggested that hormonal actions can be mediated by ROS through ROS-mediated opening of ion channels. Here, we surveyed the link between the action of IAA, oxidative burst, and calcium channel activation in a transgenic cells of rice expressing aequorin in the cytosol. Application of IAA to the cells induced a rapid and transient generation of superoxide which was followed by a transient increase in cytosolic Ca2+ concentration ([Ca2+]c). The IAA-induced [Ca2+]c elevation was inhibited by Ca2+ channel blockers and a Ca2+ chelator. Furthermore, ROS scavengers effectively blocked the action of IAA on [Ca2+]c elevation.
Previously, effect of Al ions on calcium signaling was assessed in tobacco cells expressing a Ca ... more Previously, effect of Al ions on calcium signaling was assessed in tobacco cells expressing a Ca 2+-monitoring luminescent protein, aequorin and a newly isolated putative plant Ca 2+ channel protein from Arabidopsis thaliana, AtTPC1 (two-pore channel 1). TPC1 channels were shown to be the only channel known to be sensitive to Al and they are responsive to reactive oxygen species and cryptogein, a fungal elicitor protein. Thus, involvement of TPC1 channels in calcium signaling leading to development of plant defense mechanism has been suggested. Then, the use of Al as a specific inhibitor of TPC1-type plant calcium channels has been proposed. Here, using transgenic tobacco BY-2 cells expressing aequorin, we report on the evidence in support of the involvement of Al-sensitive signaling pathway requiring TPC1-type channel-dependent Ca 2+ influx in response to salicylic acid, a key plant defense-inducing agent, but not to an elicitor prepared from the cell wall of rice blast disease fungus Magnaporthe grisea. In addition , involvement of Al-sensitive Ca 2+ channels in response to cold shock was also tested. The data suggested that the elicitor used here induces the Ca 2+ influx via Al-insensitive path, while salicylic acid and cold-shock-stimulate the influx of Ca 2+ via Al-sensitive mechanism.
Systemic acquired resistance (SAR), a natural disease response in plants, can be induced chemical... more Systemic acquired resistance (SAR), a natural disease response in plants, can be induced chemically. Salicylic acid (SA) acts as a key endogenous signaling molecule that mediates SAR in dicotyledonous plants. However, the role of SA in monocotyledonous plants has yet to be elucidated. In this study, the mode of action of the agrochemical protectant chemical probenazole was assessed by microarray-based determination of gene expression. Cloning and characterization of the most highly activated probenazole-responsive gene revealed that it encodes UDP-glucose:SA glucosyltransferase (OsSGT1), which catalyzes the conversion of free SA into SA O-b-glucoside (SAG). We found that SAG accumulated in rice leaf tissue following treatment with probenazole or 2,6-dichloroisonicotinic acid. A putative OsSGT1 gene from the rice cultivar Akitakomachi was cloned and the gene product expressed in Escherichia coli was characterized, and the results suggested that probenazole-responsive OsSGT1 is involved in the production of SAG. Furthermore, RNAi-mediated silencing of the OsSGT1 gene significantly reduced the probenazole-dependent development of resistance against blast disease, further supporting the suggestion that OsSGT1 is a key mediator of development of chemically induced disease resistance. The OsSGT1 gene may contribute to the SA signaling mechanism by inducing up-regulation of SAG in rice plants.
Indole-3-acetic acid (IAA) is the major natural auxin involved in regulation of a variety of grow... more Indole-3-acetic acid (IAA) is the major natural auxin involved in regulation of a variety of growth and developmental processes such as division, elongation and polarity determination in growing plant cells. It has been shown that dividing and/or elongating plant cells accompanies the generation of reactive oxygen species (ROS) and a number of reports have suggested that hormonal actions can be mediated by ROS through ROS-mediated opening of ion channels. Here, we surveyed the link between the action of IAA, oxidative burst, and calcium channel activation in a transgenic cells of rice expressing aequorin in the cytosol. Application of IAA to the cells induced a rapid and transient generation of superoxide which was followed by a transient increase in cytosolic Ca2+ concentration ([Ca2+]c). The IAA-induced [Ca2+]c elevation was inhibited by Ca2+ channel blockers and a Ca2+ chelator. Furthermore, ROS scavengers effectively blocked the action of IAA on [Ca2+]c elevation.
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Papers by Kenji Umemura