ARS | Publication request: Systemic Aquired Resistance Induced by Bth in Papaya

Submitted to: Physiological and Molecular Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 15, 2004
Publication Date: November 1, 2003
Citation: Zhu, Y.J., Qiu, X., Moore, P.H., Borth, W., Hu, J., Ferreira, S., Albert, H.H. 2004. Systemic aquired resistance induced by BTH in papaya. Physiological and Molecular Plant Pathology 63(5): 237-248.

Interpretive Summary: Systemic aquired resistance (SAR) is a state of broad spectrum disease resistance which can be triggered by certain pathogens. In the model plant systems arabidopsis and tobacco, SAR can be induced by application of salicylic acid or related molecules like benzothiadiazole (BTH). We determined that SAR can be introduced in papaya by relatively low concentrations of BTH, which are minimally phytotoxic. The papaya response is manifested by increased tolerance to infection by the virulent pathogen Phytophthora palmivora, by increased defense related enzyme activities (B-1,3-glucanase and chitinase), and by increased accumulation of a PR1 mRNA. Specific PR1 genes are widely used as indicators of SAR induction. Infection of untreated papaya by P. palmivora also induced B-1,3-glucanase and chitinase activities but at much lower levels. This response to P. palmivora is characteristic of a compatible interaction. Papaya has at least four members of the PR-1 gene family; BTH reduces mRNA accumulation for two of these and increases it in the other two. One of these, PR-1d, is induced over twentyfold; mRNA accumulation for this gene increased for at least 14 days after BTH treatment. In contrast, both chitinase and B-1,3-glucanase activities peaked after 1-2 days then returned to base levels at approx. 10 days. The NPR1 gene of arabidopsis was identified as a key reulatory and signal transduction component of the plant defense pathway. Papaya has an NPR1 gene that contains sructural domains conserved with arabidopsis; these domains are involved in protien-protien interactions and nuclear localization, which are essential for function in SAR of arabidopsis. The papaya NPR1 gene is expressed constitutively and is slightly induced by BTH treatment. Overall, these findings indicate the basic elements of papaya SAR resemble the pathway as described in arabidopsis and tobacco.

Technical Abstract: Systemic aquired resistance in Carica papaya L. is induced by benzothiadiazole (BTH). The response is manifested by increased tolerance to infection by the virulent pathogen Phytophthora palmivora, by increased B-1,3-glucanase and chitinase activities, and by increased accumulation of a PR1 mRNA. Infection of untreated papaya by P. palmivora also induced B-1,3glucanase and chitinase activities but at much lower levels. This response to P. palmivora is characteristic of a compatible interaction. Papaya has at least four members of the PR-1 gene family; BTH reduces mRNA accumulation of two of these and increases it in the other two. One of these, PR-1d, is induced twentyfold; mRNA accumulation for this gene increased for at least 14 days after BTH treatment. In contrast, both chitinase and B-1,3-glucanase activities peaked after 1-2 days then returned to base levels at approx. 10 days. Papaya has an NPR1 gene that contains structural domains conserved with arabidopsis; these domains are involved in protien-protien interactions and nuclear localization, which are essential for function in SAR of arabidopsis. The papaya NPR1 gene is expressed constitutively and is slightly induced by BTH treatment. Overall, these findings indicate the basic elements of papaya SAR resemble the pathway as described in arabidopsis and tobacco.