The MAPK kinase kinase GmMEKK1 regulates cell death and defense responses

Authors: XU, HUI-YANG - Zhejiang Normal University; ZHANG, CHI - Zhejiang Normal University; LI, ZHEN-CHAO - Zhejiang Normal University; WANG, ZHI-RONG - Zhejiang Normal University; JIANG, XU-XU - Zhejiang Normal University; SHI, YAFEI - Zhejiang Normal University; BRAUN, EDWARD - Iowa State University; MEI, YU - Iowa State University; QIU, WEN-LI - Iowa State University; LI, SEN - Zhejiang University; WANG, BO - China Agricultural University; XU, JUAN - Zhejiang University; Navarre, Duroy - Roy; REN, DONGTAO - China Agricultural University; CHENG, NINGHUI - Baylor College Of Medicine; Nakata, Paul; Graham, Michelle; WHITMAN, STEVEN - Iowa State University; LIU, JIANZHONG - Zhejiang Normal University

Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/18/2018
Publication Date: 8/29/2018
Citation: Xu, H., Zhang, C., Li, Z., Wang, Z., Jiang, X., Shi, Y., Braun, E., Mei, Y., Qiu, W., Li, S., Wang, B., Xu, J., Navarre, D.A., Ren, D., Cheng, N., Nakata, P.A., Graham, M.A., Whitman, S., Liu, J. 2018. The MAPK kinase kinase GmMEKK1 regulates cell death and defense responses. Plant Physiology. doi:10.1104/pp.18.00903.
DOI: https://doi.org/10.1104/pp.18.00903

Interpretive Summary: Plant diseases reduce yield, quality, and profitability. Scientists at Zhejiang Normal University (China), Iowa State University, Zheijiang University (China), China Agricultural University, Baylor College of Medicine and the USDA-ARS in Prosser, Washington, Houston, Texas and Ames, Iowa showed that silencing a soybean gene called MEKK1 altered plant metabolism to favor the activation of plant defenses, resulting in increased resistance towards downy mildew and soybean mosaic virus, but at the expense of plant growth and development. Similarities and distinct differences were observed between the same gene in soybean versus Arabidopsis, showing that same defense gene does not behave the same way in all plants. These results demonstrate mechanisms that can be used to develop crops with superior disease resistance.

Technical Abstract: Mitogen-activated protein kinase (MAPK) signaling pathways play critical roles in plant immunity. Here, we silenced multiple genes encoding MAPKs using virus-induced gene silencing (VIGS) mediated by Bean pod mottle virus (BPMV) to identify MAPK genes involved in soybean (Glycine max) immunity. Surprisingly, a strong hypersensitive response (HR) cell death was observed when soybean MAPK KINASE KINASE 1 (GmMEKK1), a homolog of Arabidopsis (Arabidopsis thaliana) MEKK1, was silenced. The HR was accompanied by over-accumulation of defense signaling molecules, salicylic acid (SA) and hydrogen peroxide (H2O2). Genes involved in primary metabolism, translation/transcription, photosynthesis, and growth/development were down regulated in GmMEKK1-silenced plants, while expression of defense-related genes was activated. Accordingly, GmMEKK1-silenced plants were more resistant to downy mildew (Peronospora manshurica) and Soybean mosaic virus (SMV) compared with control plants. Silencing GmMEKK1 reduced the activation of GmMPK6 but enhanced the activation of GmMPK3 in response to flg22 peptide. Unlike Arabidopsis MPK4, GmMPK4 was not activated either by flg22 or SA. Interestingly, transient over-expression of GmMEKK1 in Nicotiana benthamiana also induced HR. Our results indicate that GmMEKK1 plays both positive and negative roles in immunity and appears to differentially activate downstream MPKs by promoting GmMPK6 activation but suppressing GmMPK3 activation in response to flg22. The involvement of GmMPK4 kinase activity in cell death and in flg22- or SA-triggered defense responses in soybean requires further investigation.