During plant-pathogen interactions, recognition of M/PAMPs (molecules from pathogens) is crucial. These molecules trigger downstream signalling. The aim of this study was to examine the response of tomato plants to the bacterial elicitor flg22. The effects of flg22 were determined during the light and night periods. In addition, metabolite classes and metabolic pathways involved in defence signaling were studied.
During the light phase of the day, flg22 elicited rapid systemic and local defence responses. Several defence-related phytohormones were detected. The levels of DEF, PR1 and ERF1 were significantly increased in the light period. These phytohormones are regulated by ET, which plays an important role in the stomatal closure process. ET is also involved in H2O2 production.
ET was found to be important for the rapid systemic response of the tomato plants during the light period. ET also plays an important role in the JA-mediated signalling process. A one-hour long treatment with flg22 triggered a significant increase in ERF1 expression. However, changes in ERF1 transcript levels were not detected in dark periods. This could be due to the absence of NO.
The expression of PR1 and DEF were also increased in the WT leaves. However, these changes were not observed in the Nr leaves. In addition, the SA content was higher in the upper leaf level of WT leaves.
In contrast, flg22 treatments did not affect the SA content in the mutant leaves. ET and SA play important roles in the plant defence response.