Studies on the Resistance Induced by β-Aminobutyric Acid Against of Pseudoperonospora Cubensis in Cucumber and Its Resistant Mechanism
|School||Henan Agricultural University|
|Keywords||β-Aminobutyric Acid Cucumber Downy mildew Reactive oxygen species Callose Resistance or regulator-related genes Induced resistance|
Cucumber is one kind of important vegetables in the world. However, downy mildew, caused by Pseudoperonospora cubensis, is the most destructive plant disease in cucumber production areas worldwide.β-Aminobutyric acid （BABA）, a nonprotein amino acid, is a potential plant chemical inducers of resistance. Nonetheless, more information also needs to study about the resistance mechanism in the infected leaves by Pseudoperonospora cubensis induced by BABA. In this paper, the disease resistance induced by BABA and probable biochemical mechanism of the resistance against P. cubensis were studied by using the susceptible inbred line IL112 and the resistant inbred line HNAU-0023. The investigation was performed on callose and H2O2 content. The main results were as follows:1. According to the results of disease index of cucumber, we found that BABA can be acted as a kind of elicitor which can efficiently induce the resistance of cucumber against P. cubensis, particularly in the susceptible one.2. The results revealed that BABA did not induce rapid H2O2 accumulation in the invaded host cells of IL112, but it could do it in resistant one. Oxidative burst were investigated at penetration site and the cell wall of attacked inoculated resistant plant and BABA-treated susceptible one. It was confered that BABA-treated and inoculated cucumber leaves may have a fast hypersnesitive response to defeat against P. cubensis.3. The contents of two inoculated or BABA-treated lines were upward trend. The results revealed that BABA did not induce rapid callose accumulation in the invaded host celles of IL112 and HNAU-0023. Callose synthesis inhibitor DDG did not inhibit callose accumulation nor compromise the resistance induced by BABA in resistant line, but it could do it in the susceptible one.At the indicated timepoints 12, 24, 48 and 72 hpi, leaf disks of IL112 and HNAU-0023 were microscopically analyzed for callose encasement. It was confered that the rate of attacked cells were further enhanced in BABA-treated IL112 to defeat against P. cubensis. Callose synthesis inhibitor DDG did not inhibit callose encasement nor compromised the resistance.4. EF1αand UBI-ep were as reference genes for the normalization of target gene expression. To investigate the responses of six resistance or regulator-related genes associated to P. cubensis, their expression profiles were analyzed by real-time quantitative RT-PCR. As a result, Chit1,β-1,3-glucanase, Peroxidase, PAL and ETR1 were higher significantly expressed in BABA-treated and inoculated leaves of IL112. At 0 hours post inoculation （hpi）, Chit1,β-1,3-glucanase, Peroxidase, PAL, ETR1 and CTR1 showed earlier expression in BABA-treated IL112 and then its expression slowed down. Chit1,β-1,3-glucanase and PAL reached a peak at 12 hpi; ETR1 and CTR1 could be up-regulated again at 4 and 24 hpi respectively. Chit1,β-1,3-glucanase, ETR1 and CTR1 in IL112 BABA-treated and inoculated with P. cubensis could be up-regulated again at 4, 12 and 24 hpi respectively.At 4 hpi, Chit1,β-1,3-glucanase, Peroxidase, PAL, ETR1 and CTR1 showed expression in BABA-treated HNAU-0023. They were differentially suppressed from 4 to 48 hpi. Their expressions in HNAU-0023 BABA-treated and inoculated with P. cubensis reached a peak at 4 hpi, too. There were ETR1 and CTR1 with differential expression consistently detected from 4 to 48 hpi. Peroxidase could be up-regulated again at 24 hpi.5. Chit1,β-1,3-glucanase, Peroxidase and PAL in DDG- and BABA-treated IL112 could be significantly up-regulated at 0 hpi ,significantly expressed again at 48 hpi. ETR1 and CTR1 could be significantly up-regulated at 48 hpi.Chit1,β-1,3-glucanase and PAL were higher significantly expressed in ETYA and BABA IL112 than in ETYA-treated leaves.Chit1,β-1,3-glucanase and PAL were earlier and higher significantly expressed in DDG- and BABA-treated HNAU-0023 than in DDG-treated leaves.At 0 hpi, Chit1,β-1,3-glucanase, Peroxidase, PAL, ETR1 and CTR1 showed expression in ETYA-and BABA-treated HNAU-0023 and BABA-treated. Chit1,β-1,3-glucanase, Peroxidase, PAL, ETR1 and CTR1 were earlier and higher significantly expressed again. There were Chit1,β-1,3-glucanase, Peroxidase, PAL and ETR1 with differential expression consistently detected from 4 to 12 hpi.So it was confered that BABA may activate reactive oxygen species of inoculated cucumber leaves and increased resistance or regulator-related expression to defeat against P. cubensis. SA-dependant system acquired resistance pathway and the JA-dependent induced system resistance pathway finally may converge on some transcription factors and participate in the defense response of cucumber to P. cubensis.