Identification and expression analysis of peroxisome-targeted defence proteins mediating innate immunity in the model plant Arabidopsis thaliana
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Peroxisomes are single-membrane organelles that have oxidative metabolic functions. Peroxisomes carry out major functions such as lipid degradation, photorespiration and glyoxylate cycle. However, new functions have been recently reported such as peroxisome mediation in plant innate immunity. To elucidate more on peroxisomal roles in pathogen defence in plants, identification and expression analyses of both new and established peroxisome-targeted pathogen defence proteins in plants was investigated in this study. Subcellular localization analysis of four PTS1 carrying proteins with a pathogen annotation was done. In addition, gene expression analysis of established peroxisomal pathogen defence was carried out using Real-Time Quantitative PCR (qPCR). The four PTS1 carry proteins that whose subcellular localization was studied are NUDT7, NUDT15, CHAT homolog and ATP-BP. NUDT15 and CHAT homolog targeted punctuate subcellular structures, which were later confirmed to be peroxisomes in double labelling experiment with a peroxisomal marker. NUDT7 and ATP-BP failed to target any subcellular structures, were therefore, putatively reported to be cytosolic in this study. Expression analyses were done on three NHL proteins (NHL4, NHL6 and NHL25) and also on three IAN proteins (IAN8, IAN11 and IAN12) using wild type Arabidopsis Col 0 plants, by mimicking pathogen attack with exogenously applied defence hormone-salicylic acid. All the NHL and IAN genes were induced after salicylic acid treatment. In addition, co-expression analyses were done on the aforementioned NHL and IAN proteins (except for NHL25). NHL6 and IAN8 were co-expressed with other Arabidopsis defence proteins. Whereas NHL4, IAN11 and IAN12 were found not be co-expressed in the dataset generated. In conclusion, in this study, two new peroxisomal pathogen defence proteins were identified namely NUDT15 and CHAT homolog, and also NHL6 and NHL25 were induced by salicylic acid treatment.
Master's thesis in Biological Chemistry