Location: Molecular Plant Pathology LaboratoryTitle: Role of gibberellic acid in tomato defense response to potato purple top phytoplasma infection Author
|Lee, Ing Ming|
Submitted to: Annals of Applied Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/2/2012
Publication Date: 2/1/2013
Citation: Ding, Y., Wei, W., Wu, W., Davis, R.E., Jiang, Y., Lee, I., Hammond, R., Sheng, J., Shen, L., Zhao, Y. 2013. Role of gibberellic acid in tomato defense response to potato purple top phytoplasma infection. Annals of Applied Biology. 162(2)191-199. Interpretive Summary: Many diseases in agriculturally important crops are associated with infection by phytoplasmas, a group of small bacteria without a cell wall. These bacteria are capable of disrupting the balance of growth hormones inside the affected plants and inducing various symptoms. In a previous study, we found that, in tomato plants, a phytoplasma infection could cause significant reduction in internal levels of a growth hormone called gibberellic acid, and application of the growth hormone could compensate for the hormonal loss and reduce disease symptoms. In the present study, we explored the role of the growth hormone in tomato defense against phytoplasma infection. We found that the growth hormone can promote the production of other stress-coping hormones that work together to enhance the plant’s defense system. We also found that pretreatment of plants with gibberellic acid can prepare the plants for an ensuing battle with phytoplasma; the hormone-boosted defense limited the bacterial multiplication and reduced disease symptoms. Findings from the current study open new opportunities for in-depth research on roles of naturally-occurring plant hormones in disease resistance. The information is important to research scientists, students, and university professors who are studying pathogen-host interactions that result in diseases. This report will also be of interest to growers, extension personnel, and agricultural economists who are concerned with plant disease management and food security.
Technical Abstract: Infection of tomato by potato purple top (PPT) phytoplasma causes disruption of gibberellin (GA) homeostasis in the plant host. Such pathologically-induced GA deficiency can be partially reversed by exogenous application of GA. The present study was designed to explore the role of GA in tomato defense response against phytoplasmal disease, and to determine whether pretreatment with GA would protect healthy tomato seedlings from subsequent phytoplasmal infection and disease development. Our results revealed that, following exogenous GA application and subsequent PPT phytoplasma graft inoculation, there was an apparently coordinated down-regulation of the GA signaling and growth repressor gene GAI and up-regulation of genes involved in salicylic acid (SA) synthesis (ICS1), signaling (NIM1), and downstream defense responses (PRP-1). Our results also indicated that differential regulation of the above genes was correlated with an increase of activities of defense-related enzymes ß-1,3-glucanase (GLU) and chitinase (CHI). The data presented in this communication provide evidence to suggest that GA may act via DELLA and SA signaling pathways to modulate host defense in response to PPT phytoplasma infection. Although the GA pretreatment-induced defense was not sufficient to prevent a systemic infection, it reduced phytoplasma titer and significantly attenuated disease symptoms. While the actual molecular mechanism underlying the GA-induced plant defense remains elusive, findings from the current study open new opportunities for in-depth studies of the functional role of the GA signaling network during defense response against phytoplasma infection.