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22대 대한민국 국회 국회정보길라잡이 국회의원검색
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국회도서관 홈으로 정보검색 소장정보 검색
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결과 내 검색 동의어 포함

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Title Page 1

Contents 6

ABSTRACT 19

Chapter 1. Introduction 21

1.1. Background and research needs 21

1.2. Research objectives 24

1.3. Dissertation outline 25

Chapter 2. Literature Review 27

2.1. Catastrophic effects of drought stress on agricultural productivity 27

2.2. Effect of drought stress on plant growth and development 29

2.3. Drought stress alters the microbial physiology and ecosystem function 31

2.4. Survival of bacteria in drought stricken rhizosphere 32

2.5. Response of soil bacterial community to drought 34

2.6. Plant-microbe interactions to improve the physiological process associated with drought tolerance in plants 40

2.7. Mechanisms intrinsic in plant growth-promoting rhizobacteria 48

2.7.1. Phytohormone-induced drought signaling pathways 48

2.7.2. Osmoregulation by osmolytes accumulation 50

2.7.3. Mineral nutrient uptake in plants by PGPR 52

2.7.4. Production of exopolysaccharides (EPS) and biofilm formation 54

2.7.5. Altering antioxidant defense system 55

2.7.6. Induced systematic tolerance (ISR) 56

2.8. Stress tolerant plant growth-promoting rhizobacteria as biofertilizer 57

Chapter 3. Stress responsive features of mutualistic rhizobacteria proliferate drought tolerance in plant 59

3.1. Introduction 59

3.2. Material and methods 63

3.2.1. Sample collection and rhizobacterial strain isolation 63

3.2.2. Screening of drought-tolerant rhizobacteria 64

3.2.3. Evaluation of plant growth-promoting traits in vitro 65

3.2.4. Identification of the strains by amplification of 16S rRNA genes 66

3.2.5. Whole-genome sequencing and genome annotation 66

3.2.6. Plant cultivation experiments to assess the plant growth-promoting ability of selected strains 67

3.2.7. Statistical analysis 68

3.2.8. Data availability 69

3.3. Result 69

3.3.1. Screening and identification of drought-tolerant rhizobacteria 69

3.3.2. Biochemical characterization for plant growth-promoting traits 73

3.3.3. Genome properties of selected strains 73

3.3.4. Essential functional genes linked to improving drought tolerance and growth in plant 78

3.3.5. Effects of drought-tolerant rhizobacteria on plant growth 83

3.4. Discussion 87

Chapter 4. Comprehensive genome and transcriptome analyses reveal drought stimulates a new plant-bacterial interaction to alleviate stress 93

4.1. Introduction 93

4.2. Material and methods 97

4.2.1. Isolation of drought-tolerant rhizobacteria 97

4.2.2. Sample preparation for Raman spectra acquisition 98

4.2.3. Comprehensive in vitro screening for various plant growth promoting (PGP) traits 99

4.2.4. DNA isolation and whole-genome sequencing 100

4.2.5. Genome sequence analysis and annotation 101

4.2.6. Preparation of samples for transcriptomic analysis 102

4.2.7. Extraction of total RNA and high throughput sequencing 102

4.2.8. Experimental design for plant cultivation 104

4.2.9. Statistical data analysis on plant growth under drought and non-drought condition 105

4.3. Result 105

4.3.1. Phylogenetic identification of plant growth-promoting abilities of isolated drought-tolerant strain 105

4.3.2. General genome features of P. ƒluorescens DR397 106

4.3.3. Genomic insight into adaptive strategies to tolerance and plant growth promotion 109

4.3.4. Transcriptional profiling of DR397 in response to PEG induced drought and plant root exudates 116

4.3.5. Effects of P. ƒluorescens DR397 inoculation on plant growth 125

4.4. Discussion 127

Chapter 5. Drought induced synergistic trait of Sphingobacterium nripensae DR205 to promote plant drought tolerance through phytohormonal crosstalk 138

5.1. Introduction 138

5.2. Materials and methods 142

5.2.1. Screening of rhizobacteria from drought prone agricultural land 142

5.2.2. Investigation of drought tolerance capacity of the strain 143

5.2.3. Detection of drought response using Raman spectroscopy 144

5.2.4. Evaluation of plant growth-promoting features by biochemical assay 145

5.2.5. Evaluation of plant growth promotion through plant cultivate tests 146

5.2.6. De novo sequencing, assembly, and functional annotation of the genome of strain DR205 147

5.2.7. Extraction of total RNA and high throughput sequencing 148

5.2.8. Statistical analysis of plant cultivation data 150

5.3. Result 151

5.3.1. Drought tolerant strain isolated from soybean rhizosphere and its ability to promote plant growth 151

5.3.2. S. nripensae DR205 elicited growth stimulation in legume phenotypes under drought stress 153

5.3.3. General genomic properties of the strain DR205 155

5.3.4. Functional pathways and genes conferring drought tolerance and plant growth promotion traits 159

5.3.5. Gene expression analysis of DR205 revealing evolved plant-microbe interaction under drought 167

5.4. Discussion 172

Chapter 6. Conclusion 180

6.1. Summary and achievements 180

6.2. Future works 183

References 185

ABSTRACT in KOREAN 201

List of Tables 18

Table 2.1. Role of different plant growth-promoting rhizobacteria (PGPR) to improve drought tolerance in legume 43

Table 3.1. In Vitro functionality tests for plant growth promotion activity of selected drought tolerant strains 72

Table 3.2. Genomic features of drought-tolerant rhizobacterial strain 75

Table 3.3. Effects of drought-tolerant strains on plant growth parameters of Pisum sativum and Phaseolus vulgaris by direct inoculation method under drought and non-drought conditions 86

Table 4.1. Secondary metabolites and extracellular polymeric substances (EPS) produced by P. ƒluorescence DR307 115

List of Figures 14

Fig. 2.1. Links among environmental drivers, microbial physiology, community composition, and ecosystem processes 33

Fig. 2.2. The effects of drought on soils, plants and their associated bacterial communities 38

Fig. 2.3. Schematic diagram of the mechanism of plant drought tolerance induced by plant growth-promoting rhizobacteria 53

Fig. 3.1. Growth curves demonstrating the drought tolerance capacity of rhizobacteria 70

Fig. 3.2. Phylogenetic affiliation of drought-tolerant rhizobacterial strains 71

Fig. 3.3. Average Nucleotide Identity (ANI) scores between Pseudomonas strains 76

Fig. 3.4. COG categories in genome of eight drought-tolerant plant growth promotional strains 77

Fig. 3.5. Genomic features of isolated drought-tolerant rhizobacteria promoting plant growth and drought tolerance 80

Fig. 3.6. Bacterial functional pathways to synthesize phytohormones and osmolytes 81

Fig. 3.7. Gene clusters conferring antioxidant defense, rhizosphere survival and plant interacting secretion systems 84

Fig. 3.8. Characterization of drought-tolerant plant growth-promoting rhizobacteria 85

Fig. 4.1. Growth, metabolic activity, and phylogenetic affiliation of the strain DR397 108

Fig. 4.2. Nucleotide Identity (ANI) and functional classification in Cluster of Orthologous Groups of proteins (COG) 110

Fig. 4.3. Metabolic pathways and transport systems found in the genome of P. ƒluorescence DR397 113

Fig. 4.4. Transcriptomic modulation in P. ƒluorescence DR397 genes in response to drought stress and plant-bacteria symbiosis 118

Fig. 4.5. Functional enrichment analysis of highly regulated genes in P. ƒluorescence DR397 119

Fig. 4.6. Enhanced expression of the drought-inducible synergistic functional pathway in P. ƒluorescence DR397 121

Fig. 4.7. Fold changes of DR397 genes corporates in transport and metabolism of plant drought regulatory functions 123

Fig. 4.8. Expressed gene related biofilm matrix composition and niche biology 124

Fig. 4.9. P. ƒluorescence DR397 induced drought tolerance in legume cultivars evaluated by plant cultivation experiment 126

Fig. 5.1. Growth, metabolic activity, and phylogenetic affiliation of the strain DR205 152

Fig. 5.2. S. nripensae DR205 induced drought tolerance in bean cultivation experiment 154

Fig. 5.3. Nucleotide Identity (ANI) and functional gene distribution 156

Fig. 5.4. Metabolic pathways and transport systems found in the genome of S. nripensae DR205 157

Fig. 5.5. Genes related biofilm formation and colonization 162

Fig. 5.6. Transcriptomic modulation in S. nripensae DR205 genes in response to drought stress and plant-bacteria symbiosis 164

Fig. 5.7. Enhanced expression of drought-inducible synergistic functional pathway in S. nripensae DR205 165

Fig. 5.8. Functional enrichment analysis of highly regulated genes in S. nripensae DR205 168

Fig. 5.9. Gene expression analysis of highly regulated colonization functions in S. nripensae DR205 169

Fig. 5.10 Gene expression regarding energy metabolism in S. nripensae DR205 170

초록보기

 가뭄내성 미생물 군집을 포함하는 근권은 가뭄 스트레스 환경에서 식물의 생장을 촉진한다. 근권 미생물의 가뭄 복원력을 통한 식물 가뭄 저항성 향상은 복잡한 식물-미생물 상호작용에 의해 제어되고 있으나, 이에 대한 기존 지식은 전무하다. 본 연구에서는 식물의 가뭄 저항성 향상 및 생장을 촉진하기 위해 식물생장촉진 근권미생물의 가뭄 조절 대사 경로를 조사하였다.

본 논문에서, 1000개의 세균 균주가 한국 강원도의 가뭄 취약 지역에서 재배되는 콩과 작물 근권에서 분리 동정되었다. 가뭄 조건에서 동정 균주의 가뭄내성과 대사활성은 동위원소인 중수 (D₂O) 표지를 이용한 라만분광법을 통해 조사되었으며, 세포 외 식물생장촉진 기능을 평가하였다. 16S rRNA 염기서열 기반 계통 분석 결과 가뭄내성을 가진 상위 8 개 균주는 Sphingobacterium, Glutamicibacter, Paenibacillus, Stenotrophomonas, Pseudomonas 속에 속하였다. 8개의 선별된 가뭄내성 균주의 전장유전체 분석을 통해 식물 가뭄 저항성을 개선하기 위한 스트레스 적응, 생존 매커니즘 및 식물 공생 상호작용과 관련된 가뭄내성 식물생장촉진 근권미생물의 핵심 유전체계를 발견했다. Pseudomonas fluorescence DR397의 RNAseq 기반 전사체 분석을 통해 삼투 보호제 및 세포 외 고분자 화합물(EPS)의 생산으로 식물의 가뭄 스트레스를 완화하는 식물-미생물 상호작용이 연구되었다. 또한 Sphingobacterium nripensae DR205의 유전체 및 전사체 분석은 동시 분자 반응을 통한 피토호르몬 기반의 가뭄 신호 물질의 활성화를 밝혀냈다. 콩과 작물 2종(Pisum sativum, Phaseolus vulgaris)을 이용한 식물재배 실험은 가뭄 스트레스 조건에서 가뭄내성 균주가 싹 길이, 뿌리 길이, 생 중량, 건조중량을 유의하게 증가시키는 것을 보여주었다.

이러한 연구 결과는 가뭄내성 미생물의 스트레스 반응 특성을 구명하여, 역동적 기능 전환을 통해 미생물이 식물 근권에서 번성하도록 하고 궁극적으로 식물의 가뭄 저항성을 향상시켰다.

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