Location: Molecular Plant Pathology
Title: Potato purple top phytoplasma-induced disruption of gibberellin homeostasis in tomato plants Authors
|Lee, Ing Ming|
Submitted to: Annals of Applied Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 8, 2012
Publication Date: January 2, 2013
Citation: Ding, Y., Wu, W., Wei, W., Davis, R.E., Lee, I., Hammond, R., Sheng, J., Shen, L., Jiang, Y., Zhao, Y. 2013. Potato purple top phytoplasma-induced disruption of gibberellin homeostasis in tomato plants. Annals of Applied Biology. 162:131-139. Interpretive Summary: Many agriculturally important crops are vulnerable to attacks by a group of small bacteria called phytoplasmas. Diseases caused by such bacteria often exhibit symptoms indicative of growth regulator (hormone) disorder. In the present study, we found that a phytoplasma affecting tomato, potato, and several other vegetable crops could cause significant reduction in internal levels of gibberellic acid, a naturally-occurring plant hormone involved in diverse physiological processes. We also found that the loss of the hormone was mainly due to the suppression of the activities of key genes responsible for production of the hormone. External application of the hormone at early stages of phytoplasma infection could compensate the hormonal loss and therefore ease disease symptoms. Findings from the present study provide new knowledge on phytoplasma-host interactions and offer clues to devising practical approaches to control phytoplasmal diseases. The information is important to research scientists, students, and university professors who are studying pathogen-host interactions and mechanisms of plant 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: Phytoplasmas are phloem-inhabiting, cell wall-less bacteria that cause numerous plant diseases worldwide. Plants infected by phytoplasmas often exhibit various symptoms indicative of hormonal imbalance. In the present study, we investigated the effects of potato purple top (PPT) phytoplasma infection on gibberellin homeostasis in tomato plants. We found that PPT phytoplasma infection caused a significant reduction in endogenous levels of gibberellin acid (GA3). The decrease in GA3 content in diseased plants was co-related with down regulation of genes encoding key enzymes involved in the biosynthesis of bioactive GAs and their precursors. Exogenous application of GA3 was able to restore the GA content in infected plants to levels comparable to those in healthy controls, and to attenuate the characteristic “big bud” symptoms induced by the phytoplasma. Results from this study also revealed that, in phytoplasma-infected plants, key GA biosynthesis genes GA20ox1 and GA3ox1 failed to respond to reduced GA3 content, suggesting a de-sensitization of the GA biosynthesis negative feedback loop. We hypothesize that such de-sensitization may represent a central element of the phytoplasma-induced disruption of GA homeostasis and pathogenesis.