Abstract: 【Objective】The objective of this study is to clarify the effect of induced etr1-1 expression on petunia response to infection by Botrytis cinerea, the causal agent of gray mold disease. 【Method】Detached leaves of GVG: etr1-1 transgenic petunias treated by DEX were inoculated with B. cinerea, then the regulation mechanism of etr1-1 was investigated by observing disease symptoms, measuring disease severity and analyzing gene expression by quantitative RT-PCR and semi-quantitative RT-PCR. 【Result】Induced etr1-1 expression by dexamethasone resulted in the retarded senescence and reduced disease symptoms on detached leaves. During the period of inoculation, the percentage of increased disease incidence was 0 on DEX-treated leaves, whereas 66.77% on control leaves. The growth rate of the leaf lesions on DEX-treated leaves was 4.69 mm•d-1, whereas 6.29 mm•d-1 on control leaves. qRT-PCR and semi-qRT-PCR provided the following results. The extent of decreased disease incidence was negatively correlated with the etr1-1 expression. Following prolonged induction time, the level of etr1-1 expression was enhanced on DEX-treated leaves and obtained the peak at 3rd day after DEX treatment. 10.71-fold changes were increased on mock-inoculating leaves than that on B. cinerea-inoculating leaves. The maximum expression of Bcact was obtained at 1 dpi on DEX-treated leaves, whereas, at 2 dpi on control leaves. The maximum level of Bcact expression was 20-fold lower on DEX-treated leaves than that on control leaves. Infection of B. cinerea activated CP10 expression and caused the senescence symptom. In comparison, 23.6-fold changes were decreased on DEX-treated leaves than on control leaves. The expression of ACO exhibited a decline after an up on both DEX-treated and control leaves. The peak of expression level was observed at 2 dpi. The peak of expression of ACO was only 6.75 on DEX-treated leaves, which suggested 7.33-fold lower than that on control leaves. On DEX-treated leaves with induced etr1-1 expression, repressed genes expressions in ethylene/JA pathway decreased ERF4 and ERF8 expression and consequently reduced pathogenesis-related gene expression. The expressions of ERS1 and ETR2 were observed and the peak of expression came out at 3 dpi on both DEX-treated and control leaves, however, 51-fold lower expression was observed on DEX-treated leaves than that on control leaves. The expression was suppressed at 1 and 2 dpi, and activated at 3 dpi on DEX-treated leaves. Following the prolonged inoculation time, the level of EIN2 expression was enhanced on control leaves. It was found that the maximum expression on DEX-treated leaves was 31.58-fold lower than that on control leaves. The expression of EIL1 showed the similar patterns as that of EIN2. It was observed that 2-fold lower expression of EIN2 on DEX-treated leaves than that on control leaves. AOC and COI1 played important roles in the biosynthesis and signal pathway of jasmonic acid. The expression of AOC and COI1 was repressed at 1-2 dpi and activated at 3 dpi on DEX-treated leaves, however, the expression level was increased following the prolonged inoculation time on control leaves. It was found that 12.96-fold lower expression on DEX-treated leaves than on control leaves. The expression of COI1 was discovered and obtained the peak at 3 dpi, regardless of DEX-treated leaves and control leaves. It was observed that 6.14-fold lower expression of COI1 on DEX-treated leaves than on control leaves. The expression of ethylene response factors (ERFs), as downstream components, integrated the ethylene and JA signaling pathway. The expression of ERF4 showed up before a decrease pattern on DEX-treated leaves. The expression level of ERF4 showed rising patterns following inoculation. The expressions of ERF8 displayed ascend patterns following the prolonged inoculation time, regardless of DEX-treated and control leaves. It was found that 2.96- and 3.52-fold lower expression of ERF4 and ERF8 on DEX-treated leaves than on control leaves. Little expression of pathogenesis-related genes was monitored on DEX-treated leaves and the peak of all genes was lower than 10, whereas, the expression was enhanced on control leaves, such as, the maximum level of expression of PR1, EX-CHI, OSM, Defense1 and AC-CHI was 10 521.11, 184.95, 184.96, 23.39 and 14.58, respectively.【Conclusion】Induced etr1-1 expression delayed the senescence of leaves of petunia caused by B. cinerea and was consequently responsible for tolerance of GVG: etr1-1 transgenic petunias to B. cinerea.

Key words: petunia ×, hybrida ‘Mitchell diploid&rsquo, Botrytis cinerea , ethylene , jasmonic acid , senescence , defense response