Title Page

Contents

ABSTRACT IN KOREAN 8

Ⅰ. INTRODUCTION 10

Ⅱ. MATERIALS AND METHODS 13

1. Bacterial strains and growth conditions 13

2. Screening of mutant library 13

3. Generation of the complemented strain and green fluorescence protein (GFP)-tagging strains 15

4. Bacterial growth in methionine-limited media 15

5. Pathogenicity tests 16

6. PCWDE assays 17

7. RNA sequencing and data analysis 18

8. Statistical analysis 19

Ⅲ. RESULTS 21

1. In vitro transposon screen selects the metC mutant inducing Pcc21 biofilm formation 21

2. Inactivating metC becomes a methionine auxotroph 23

3. Inactivating metC requires a higher concentration of exogenous methionine to overcome auxotrophy 26

4. Inactivating metC decreases soft rotting symptoms in Chinese cabbages and potato tubers, regardless of extracellualr enzymatic and motile activities 28

5. Inactivating metC requires a large amount of exogenous methionine for virulence 32

6. Differentially expressed genes (DEGs) between Pcc21 wild-type and ΔmetC at the early infection stage 35

Ⅳ. DISCUSSION 40

Ⅴ. CONCLUSION 44

REFERENCES 45

Abstract 52

Table 1. Summary of significantly differentially expressed genes (DEGs) related to methionine biosynthesis and transporter and... 39

Fig. 1. Verification of the metC mutant in Pcc21. 24

Fig. 2. Requirement of exogenous methionine to overcome methionine auxotrophy 27

Fig. 3. Virulence and growth of the metC mutant on Chinese cabbage and potato tuber. 30

Fig. 4. Plant cell-wall degrading enzymes (PCWDEs) activities and swimming motility of ΔmetC. 31

Fig. 5. Growth and viability of the metC mutant on Chinese cabbage for 36 hpi. 33

Fig. 6. Requirement of exogenous methionine to restore virulence of the metC mutant on potato tuber. 34

Fig. 7. Comparative transcriptomic analysis in Pcc21 wild-type and the metC mutant infecting to Chinese cabbage slices at 4 hpi. 38