|LIU, JIAN-ZHONG - Iowa State University
|BRAUN, EDWARD - Iowa State University
|QUI, WEN-LI - Iowa State University
|SHI, YA-FEI - Zhejiang University
|MARCELINO-GUIMARAES, FRANCISMAR - Embrapa
|Navarre, Duroy - Roy
|HILL, JOHN - Iowa State University
|WHITMAN, STEVE - Iowa State University
Submitted to: Molecular Plant-Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/29/2014
Publication Date: 8/1/2014
Citation: Liu, J., Braun, E., Qui, W., Shi, Y., Marcelino-Guimaraes, F., Navarre, D.A., Hill, J., Whitman, S. 2014. Positive and negative roles for soybean MPK6 in regulating defense responses. Molecular Plant-Microbe Interactions. 27:824-834.
Interpretive Summary: A limitation in producing crops with superior ability to resist disease is incomplete understanding of the complex mechanisms plants use for defense. This work shows that a gene called MPK6 that is found in solanaceous plants, arabidopsis and soybean. Interestingly, either increasing or decreasing the amount of MPK6 in plants enhanced disease resistance to powdery mildew and Soybean mosaic virus, indicating a complex role for MPK6. A more precise understanding of how plants resist disease will improve crop quality and contribute to food security.
Technical Abstract: It has been well established that MPK6 is a positive regulator of defense responses in model plants such as Arabidopsis and tobacco. However, the functional importance of soybean MPK6 in disease resistance has not been investigated. Here, we showed that silencing of GmMPK6 in soybean using virus-induced gene silencing mediated by Bean pod mottle virus (BPMV) caused stunted growth and spontaneous cell death on the leaves, a typical phenotype of activated defense responses. Consistent with this phenotype, expression of pathogenesis-related (PR) genes and the conjugated form of salicylic acid were significantly increased in GmMPK6- silenced plants. As expected, GmMPK6-silenced plants were more resistant to downy mildew and Soybean mosaic virus compared with vector control plants, indicating a negative role of GmMPK6 in disease resistance. Interestingly, over-expression of GmMPK6, either transiently in N. benthamiana or stably in Arabidopsis, resulted in HR-like cell death. The HR-like cell death was accompanied by increased PR gene expression, suggesting that GmMPK6, like its counterpart in other plant species, also plays a positive role in cell death induction and defense response. Using bimolecular fluorescence complementation analysis, we determined that GmMKK4 might function upstream of GmMPK6 and GmMKK4 could interact with GmMPK6 independent of its phosphorylation status. Taken together, our results indicate that GmMPK6 functions as both repressor and activator in defense responses of soybean.