| Summary: | 博士 === 國立中興大學 === 生物科技學研究所 === 107 === Global climate change become an important issue in agriculture. Frequent natural disasters cause a huge economic loss every year. Therefore, improving crop resistance against biotic and abiotic stresses is an emerging issue now. Fortunately, the new techniques such as next-generation sequencing incorporating with big data analysis allow us to facilitate the breeding process or improve the efficiency of bio-agents such as fungicides without further harming the environment.
To better deal with the environmental stimuli, we need to understand the plant responses against biotic/abiotic stresses. In CHAPTER II of this thesis, an Arabidopsis-Pseudomonas syringae pv. tomato DC3000 model was used for studying of plant defense responses. Mutants of the second largest family of membrane kinases, Lectin receptor-like kinases (LecRKs), were studied to understand how plants sense pathogens and induce their resistance toward the pathogens. In this chapter, I identified a G-type LecRK (G-LecRK) mutant, which was more sensitive after challenging Pst DC3000 compared to Col-0 wild type. This receptor, G-LecRK-I.2, was involved in stomatal immunity and was required for Pst DC3000 or flg22, a bacterial-derived peptide, induced stomatal closure. This receptor interacts with FLS2/BAK1 defense complex and affects Ca2+, NO, and ROS signaling in guard cells. Besides, G-LecRK-I.2 affecting stomatal immunity is probably through direct regulation of AHA1 activity and indirect regulation of RbohD- or other Rboh-mediated stomatal closure. In CHAPTER III, I have concluded the finding of G-LecRK-I.2 and future perspectives in LecRK studies.
Understanding the process of how pathogens infect plants is also important to improve the crop production. Therefore, in APPENDIX A, a bacterial pathogen, Xanthomonas oryzae pv. oryzae (Xoo), that causes the rice blight disease was focused. In the study, I used comparative genomics and other molecular markers to identify different populations of Xoo and how these Xoo strains affected gene expressions of the host, Oryza sativa subsp. japonica TNG67. Five populations of Xoo in Taiwan were identified, and two of them were dominant in Taiwan. In addition, by comparing with available Xoo genome sequences, I discovered that type VI secretion system 2 (T6SS-2) was important in Xoo-rice interaction. Besides, through the complete genome sequences of two Taiwanese Xoo strains, XF89b and XM9, done in this study, an evolutionary relationship of Taiwanese strains with reference strains collected from other countries was also provided.
Last, in APPENDIX B, I studied one of the potential bio-agent, Photorhubdus luminescens (Pl) 0813-124, which has two different phase variants in morphology. Pl 0813-124 Phase 1 had a high anti-fungal and anti-bacterial activity as well as a pesticide activity. However, Pl 0813-124 Phase 2 only had weak or no anti-fugus and pesticide activity. Phase 2 came from Phase 1, and Phase 2 could not reverse to Phase 1 in this case. Through the comparative genomics of these two phases, a 20-kb deletion in the genome of Phase 1 strain was identified. This region might encode some important proteins that contribute to anti-microbe activities.
In short, in this thesis, I carried out three studies. First, I investigated the functions of a novel family of plant receptors that is recently discovered as a potential PAMP/DAMP sensing receptor family. I found an uncharacterized receptor, G-LecRK-I.2, that is involved in stomatal immunity. Also, I described a strategy in how to deal with agricultural problems from basic researches to applications through the studies on Xoo and Pl. This thesis provides information on the new direction of plant breeding and pathogen controls in agriculture.
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