Induction Of Systemic Acquired Resistance To Tmv With PeaT1 And The Mechanism In Tobacco

Activator protein PeaT1 is a kind of newly discovered proteinaceous elicitors isolated from Alternaria tenuissima by our laboratory. Previous studies had demonstrated that PeaT1 expressed by E. coli could induce plant resistance to pathogen. Here, we reported the systemic acquired resistance to tobacco mosaic virus in tobacco plant and signal transduction pathway. The present study will provide a theoretical basis for protein-plant interaction and elucidation of molecular mechanism of PeaT1 in inducing disease resistance in plants. The results are summarized as follows:1. PeaT1 was expressd in E. coli and purifid with anion exchange chromatography of a HisTrapTM HP and Mono QTM 5/50 GL column. . Bioassay results confirmed that the PeaT1-treated plants exhibited enhanced systemic resistance with a significant reduction in number and size of TMV lesions on tobacco leaves as compared with control. The lesion inhibition was up to 54.05% and the reduction in lesion size was 31.3%. Besides, we also observed the delay of 6 hours in lesions appearance on PeaT1 treated tobacco plants.2. PeaT1 induced defense response of tobacco inhibited the proliferation of the TMV virus, but PeaT1 exhibited no visible influences on TMV virus inactivating in vitro. The bioassay of half leaf lesions in Nicotiana tabacum cv. Samsun-NN after 5 day PeaT1 treatment showed that the number of lesion in the half leaf of PeaT1 treatments was only 65.87% of that in water treatment half leaf. More precise results of real-time quantitative RT-PCR showed that the copies of TMV-CP gene apparently reduced in PeaT1 treatments leaf and the inhibition rate was up to 75.4%. This result was is consistent with that of assay of half leaf lesions.3. PeaT1 treatment induced evident changes in lignin, defense-related enzymes and the marker genes of systemic acquired resistance. The lignin accumulation increased rapid at 5th day and reached to peak at 6th day after PeaT1 treatment with PeaT1 in the untreated upper (systemic) leaves. The enzyme activities of PPO and POD increased compared with the control. the transcription level of PR1a,PR1b genes were upregulated after PeaT1 treatment, which was in a time-dependent manner.4. SA signaling transduction pathway was involved in systemic acquired resistance induced by activator protein PeaT1 in tobacco.The Quantitative RT-PCR analysis revealed that the expression level of SAR marker genes PR1a, PR1b, SA pathway key genes NPR1 and SA systemic key enzyme PAL had increased 23.71, 19.95, 9.875, 8.255 fold respectively after PeaT1 treatment. However, there was no up-regulated expression of PDF1.2, the marker gene of Jasmonic acid (JA) and Ethylene signal transduction pathway. The accumulation of SA increased and reached to peak at 24 h after PeaT1 inducement, which increased by 3 times compared with the control.5. Activator protein PeaT1 cound not induce enhancement of disease resistance against TMV in nahG transgenic tobacco plants. The transcription of systemic acquired resistance marker genes had not upregulated. These results confirmed that PeaT1 activation of the defense responses in tobacco was mediated by salicylic acid signaling pathway.