KYUDAI NEWS KYUSHU UNIVERSITY CAMPUS MAGAZINE Spring 2014 No.25

12/28

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(ht1-2)!cdi2!(ost1)!cdi3!(slac1-2)!ht1-1!WT!ht2 (patrol1)!19.0!24.0!21.5!(ºC)!AB!(ºC)!-1.0!3.4!1.2!Fig. 2ht1-2!he continuing rise in atmospheric CO2 concentration is predicted to have diverse and dramatic effects on the productivity of agriculture, plant ecosystems and gas exchange. Stomata in the epidermis, formed by pairs of guard cells, serve as major gateways for gas exchange between plants and their environments, and provides the gate for the exchange of CO2 and water between plants and the atmosphere, processes vital to plant life. Opening of stomata is stimulated by low CO2 concentrations and light whereas stomatal closure occurs in response to high CO2, darkness and shortage of water. Guard cells integrate these signals and appropriately adjust the stomatal pore apertures to optimize growth performance. Leaf temperature provides a convenient indicator of transpiration, and can be used to detect mutants with altered stomatal control. To identify genes that function in CO2 responses in guard cells, we have isolated CO2 insensitive mutants from a model plant Arabidopsis through high-throughput leaf thermal imaging (Fig.1). Here, I will introduce four novel components of stomatal function that were identied through the genetic and functional analysis of CO2 response mutants.The rst mutant with impaired in CO2 response isolated by thermal imaging was ht1 (high leaf temperature 1) (Fig.2). Plants carrying the strong ht1-2 allele are completely impaired in stomatal CO2 responses, however, they show functional responses to blue light. This indicates that HT1 is a central regulator of stomatal CO2 signaling. Further analyses demonstrated that HT1 is a protein kinase expressed mainly in guard cells, and that the HT1 kinase activities of the mutants, dominant negative transgenic plants and wild-type plants corresponded to their ability to preform stomatal responses to CO2. Evidently, phosphorylation by HT1 kinase is an essential process in CO2 signaling.The stomatal pore aperture depends on the transport of ions and organic metabolites across guard-cell membranes. Increased CO2 concentration has been shown to enhance anion channel activity proposed to mediate efux of osmoregulatory anions from guard cells during stomatal closure. Malate and Cl- efux from the guard cells causes membrane depolalization, which drives *1 Hashimoto M, Negi J, Young J, Israelsson M, Schroeder JI, Iba K. Arabidopsis HT1 kinase controls stomatal movements in response to CO2. (2006) Nature Cell Biology 8: 391-397.Highlight of Recent ResearchPublications*2 Negi J, Matsuda O, Nagasawa T, Oba Y, Takahashi H, Kawai-Yamada M, Uchimiya H, Hashimoto M, Iba K. (2008) CO2 regulator SLAC1 and its homologues are essential for anion homeostasis in plant cells. Nature 452: 483-486. Kyudai News No.2511New Approaches to the Plant CO2 Sensing and Fig.1 Strategy for the isolation of Arabidopsis mutants using altered CO2 responses indicated by leaf temperature.Fig.2 Phenotype of CO2 response mutants. (A) Thermal image of plants subjected to low CO2 concentration. Plants exhibit lower leaf temperatures. (B) Thermal image of plants subjected to high CO2 concentration. Plants exhibit higher leaf temperatures. (C) Image of leaf temperature change in response to CO2. This image displays the subtraction of image (A) from image (B). The arrow indicates a mutant plant showing impaired CO2-dependent leaf temperature change. (A) Thermal image of plants subjected to low CO2 concentration. ht mutants exhibit higher leaf temperatures than wild-type (WT) plants. (B) Subtractive thermal image of plants when transferred from high to low [CO2]. cdi (carbon dioxide insensitive) mutants show a CO2-insensitive phenotype.HT1 protein kinase functions in response to CO2-specic signaling pathways*1SLAC1 anion channel is essential for ion homeostasis in guard cells*2T

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