Location: Corn Insects and Crop Genetics ResearchTitle: Soybean homologs of MPK4 negatively regulate defense responses and positively regulate growth and development Author
Submitted to: Journal of Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/31/2011
Publication Date: 11/30/2011
Citation: Liu, J., Horstman, H.D., Braun, E., Graham, M.A., Zhang, C., Navarre, D., Lee, Y., Nettleton, D., Hill, J.H., Whitham, S.A. 2011. Soybean homologs of MPK4 negatively regulate defense responses and positively regulate growth and development. Journal of Plant Physiology. 157(3):2363-1378. Interpretive Summary: MAP kinases activates other proteins involved in cell signaling and has been shown to activate defense responses to pathogens in several plant species. However, their involvement in defense in crop species has not been investigated. To understand how MAP kinases contributes to defense in soybean, we wanted to turn off(silence) these genes to see how disease resistance changed. Of the 30 genes targeted, silencing of GmMAPK4 resulted in stunted plants with lesions of dead cells on the leaves and stems. This response is characteristic of an activated defense response. To confirm this result, we evaluated the activity of other genes known to be involved in plant defense and the concentration of known defense compounds in the GmMAPK4 silenced plants. Our results indicate that GmMAPK4 regulates the defense response and plant growth. This study identified a key regulator of the defense response, conserved across plant species. In addition, it identified other defense-related genes that could be targets for crop improvement. With their identification, these genes can be used by researchers and breeders for developing soybean cultivars with improved resistance to harmful pathogens.
Technical Abstract: MAP kinase cascades play important roles in disease resistance in model plant species such as Arabidopsis and tobacco. However, the importance of MAP kinase (MAPK) signaling pathways in disease resistance of crops is still largely uninvestigated. To better understand the role of MAPK signaling pathways in disease resistance in soybean (Glycine max), 20 and 10 genes encoding distinct MAPKs and MAPKKs, respectively, were silenced using virus-induced gene silencing (VIGS) mediated by Bean pod mottle virus (BPMV). Among the plants silenced for various MAPKs and MAPKKs, GmMAPK4-silenced plants displayed strong phenotypes including stunted stature and spontaneous cell death on the leaves and stems – the characteristic hallmarks of activated defense responses. Microarray analysis showed that genes involved in defense responses, such as those in salicylic acid (SA) and jasmonic acid (JA) pathways were significantly up-regulated in GmMAPK4-silenced plants, whereas the genes involved in growth and development, such as those in auxin signaling pathways and in cell cycle and proliferation, were significantly down-regulated. As expected, SA and H2O2 accumulation was significantly increased in GmMAPK4-silenced plants. Accordingly, GmMAPK4-silenced plants were more resistant to downy mildew and Soybean mosaic virus (SMV) compared to vector control plants. Using bimolecular fluorescence complementation (BiFC) analysis and in vitro kinase assays, we determined that GmMKK1 and GmMKK2 might function upstream of GmMPK4. Taken together, our results indicate that GmMPK4 is a negative regulator of SA accumulation and defense response but a positive regulator of plant growth and development and its function is evolutionally conserved across plant species.