The process of topping elicits many responses in the tobacco plant, including an increase in
nicotine biosynthesis, and the secondary growth of roots. Some topping responsive
miRNAs and genes have been identified in our previous study, but the mechanism of the tobacco response to topping has not yet been fully elucidated. In this study, topping responsive
proteins isolated from tobacco roots were screened using two-dimensional electrophoresis. Of the
proteins identified,
calreticulin and
auxin-responsive
protein indole acetic acid (IAA9) were involved in the secondary growth of roots;
leucine-rich repeat
disease resistance,
heat shock protein 70, and
farnesyl pyrophosphate synthase 1 were involved in the wounding stress response; and
F-box protein played an important role in promoting the ability of
nicotine synthesis after topping. In addition, we identified five tobacco
bHLH proteins (NtbHLH, NtMYC1a, NtMYC1b, NtMYC2a, and NtMYC2b) related to
nicotine biosynthesis. NtMYC2 was suggested to be the main positive
transcription factor, with NtbHLH
protein being a negative regulator in the
jasmonic acid (JA)-mediated activation of
nicotine biosynthesis after topping. Tobacco topping activates a comprehensive range of biological processes involving the IAA and JA signaling pathways, and the identification of
proteins involved in these processes will improve our understanding of the topping response.