Primary Study On Mechanisms Ofβ-aminobutyric Acid Induced Resistance Against Phytophthora Infestans In Potato

β-aminobutyric acid (BABA) is a non-protein amino acid which can induce systemic resistance against a wide range of pathogens in numerous plant species. But the resistance mechanisms induced by BABA were differential in various plant pathosystems. In order to further look into the mechanisms of BABA induced resistance against Phytophthora infestans in potato, we observed infection process on the leaves pre-treated with BABA, and examined the defense reactions and signaling pathways in this study. At the same time, we hope to identify the function of resistance harbored by StWRKY5, a gene with augmented expression induced by BABA in early period. The main results are as follows:1. After potato leaves were pretreated with BABA, the leaves were inoculated with P. infestans isolates Ljx18and88069. Pathogen structures were observed by a fluorescence microtechnic. The germination rate in BABA pretreated plants decreased, especially at the early time (0-24hpi). Besides, in BABA pretreated potato leaves, there was a downtrend in the frequency of appressorium formation compared to that of the untreated plants. These indicated that BABA pretreatment has caused a pathogen infection suppression in early cases.2. The defense-related responses induced by BABA were observed at the histochemical level. On BABA-treated leaves, H2O2accumulation was detected in the epidermic cells as early as6hpi; callose deposition was detected in the penetration site as well as nearby cells within24hpi, and a rapid HR occurred at the same time. While, on the control leaves, H2O2accumulation was detected at12hpi, only a little callose was detected at24hpi, and there was no HR phenomenon. Thus, BABA pretreated leaves can strongly triggered H2O2accumulation callose deposition and HR at the earlier time when attacked by P. infestans.3. StCOⅡ-RNAi lines and NahG transgenic lines were selected for BABA treatment and P. infestans challenge inoculation. The results showed that StCOⅡ-RNAi lines and control plants demonstrated same level of induced resistance against P. infestans after BABA pretreatment, but in NahG lines BABA failed to induce the resistance. These results suggest that BABA-induced resistance of potato against P. infestans requires SA signaling pathway, and may not require JA signaling pathway.4. Over-expression vector of StWRKY5was conducted and transformed into potato cultivar E3, and seven over-expressed transgenic lines were obtained. Real-time quantitative PCR analysis showed that the expressions of StWRKY5in transgenic lines are significantly higher than that in control plants. We selected three of highest efficiency over-expressed transgenic lines for P. infestans challenge inoculation. It showed that the lesion area of StWRKY5transgenic plants are lesser than of control, and implied that StWRKY5may participate in the process of positive regulation of potato late blight resistance.