Regulation of salicylic acid, yeast elicitor, and chitosan signaling in Arabidopsis guard cells

of Thesis 研究科 School Graduate School of Natural Science and Technology 専 攻 Division Bioscience 学生番号 Student No. 51422453 氏 名 Name Mohammad Issak 学位論文題目 Title of Thesis(学位論文題目が英語の場合は和訳を付記) Regulation of salicylic acid, yeast elicitor, and chitosan signaling in Arabidopsis guard cells (シロイヌナズナ孔辺細胞におけるサリチル酸、酵母エリシター、キトサンシグナリン グの制御) 学位論文の要旨 Abstract of Thesis The volatile phytohormone salicylic acid (SA) and elicitors, yeast elicitor (YEL) and chitosan (CHT), induce stomatal closure similar to abscisic acid (ABA) and methyl jasmonate (MeJA). SA is involved in endogenous signaling, mediating in plant defense against pathogens. SA induces stomatal closure accompanied by peroxidase-mediated extracellular reactive oxygen species (ROS) production and intracellular ROS accumulation. However, detailed signaling of SA in guard cells remains to be clarified. Stomatal closure is induced not only by the phytohormones but also by elicitors. YEL, CHT, and ABA induce stomatal closure accompanied by ROS production, cytosolic alkalization, [Ca 2+ ]cyt oscillation, and activation of S-type anion channel leading to stomatal closure. Fungal elicitors induce SAG contents and play a role for defense responses. Both elicitors share some signal components with ABA signaling in guard cells. However, ABA signal transduction has been extensively studied, but little is known about SA, YEL, and CHT signal transduction. ABA, MeJA, and SA are major phytohormones of cellular signal transduction pathways mediating various biotic and abiotic stress responses. It has been reported that endogenous ABA is involved in MeJA-induced stomatal closure and MeJA priming is required for AITC-induced stomatal closure. However, it has not yet been elucidated whether these phytohormones involved in SA, YEL, and CHT signaling in Arabidopsis guard cells. 氏名 Name Mohammad Issak In Chapter 2, I investigated involvement of endogenous ABA and MeJA in SA, YEL, and CHT-induced stomatal closure in Arabidopsis. I examined SA-, YEL-, and CHT-induced stomatal closure in wild-type and aba2-2 mutants. SA, YEL, and CHT induced stomatal closure in the wild-type plants and aba2-2 mutants. FLU did not inhibit SA-, YEL-, and CHT-induced stomatal closure in wild-type plants. FLU alone has no effect on stomatal closure in the wild-type plants. I also investigated SA-, YEL-, and CHT-induced stomatal closure in the wild-type and aos mutants. SA, YEL, and CHT induced stomatal closure in the wild-type and aos mutants. FLU did not inhibit SA-, YEL-, and CHT-induced stomatal closure in the aos mutants. FLU alone also has no effect on stomatal closure in the aos mutants. These results suggest that neither endogenous abscisic acid nor jasmonates is involved in SA-, YEL-, and CHT-induced stomatal closure in Arabidopsis. In Chapter 3, I examined involvement of endogenous salicylic acid in YELand CHT-induced stomatal closure using Arabidopsis (Arabidopsis thaliana) wild-type (Col-0) and SA-deficient nahG transgenic lines. I found that YEL and CHT induced stomatal closure in the wild-type plants but not in the nahG transgenic lines. On the other hand, SA at 50 μM after the YEL or CHT application induced stomatal closure in the nahG plants. I investigated YELand CHT-induced extracellular reactive oxygen species (ROS) production in the whole leaves of wild-type and nahG plants. I found that YEL and CHT induced extracellular ROS production in the whole leaves of wild-type plants but not in the nahG plants. I also investigated YELand CHT-induced intracellular ROS accumulation in the wild-type and nahG guard cells. I found that YEL and CHT induced intracellular ROS accumulation in the wild-type guard cells but not in the nahG guard cells. However, SA at 50 μM in the presence of YEL or CHT induced extracellular ROS production in the whole leaves and intracellular ROS accumulation in the guard cells of nahG plants. I also examined SA-, YEL-, and CHT-induced cytosolic alkalization in nahG guard cells. I observed that SA, YEL and CHT induced cytosolic alkalization in the wild-type guard cells, whereas, SA-, YEL-, and CHT-induced cytosolic alkalization was impaired in the nahG guard cells. In contrast, SA at 50 μM just after YEL or CHT application induced cytosolic alkalization in the nahG guard cells. SA at 50 μM, which is not enough concentration to evoke SA responses in the wild-type, had no effect on the nahG plants. Finally, I examined YELand CHT-induced [Ca 2+ ]cyt elevation in the wild-type and nahG guard cells. I found that YEL and CHT induced [Ca 2+ ]cyt elevation in the wild-type guard cells but not in the nahG guard cells. In contrast, SA at 50 μM just after YEL or CHT application induced [Ca 2+ ]cyt elevation in the nahG guard cells. Taken together my results suggest that endogenous SA could be involved in YEL and CHT signal transduction leading to stomatal closure in Arabidopsis.