Soybean Homologs of MPK4 Negatively Regulate Defense Responses and Positively Regulate Growth and Development    

Abstract

Mitogen-activated protein kinase (MAPK) cascades play important roles in disease resistance in model plant species such as Arabidopsis (Arabidopsis thaliana) and tobacco (Nicotiana tabacum). However, the importance of MAPK signaling pathways in the disease resistance of crops is still largely uninvestigated. To better understand the role of MAPK signaling pathways in disease resistance in soybean (Glycine max), 13, nine, and 10 genes encoding distinct MAPKs, MAPKKs, and MAPKKKs, respectively, were silenced using virus-induced gene silencing mediated by Bean pod mottle virus. Among the plants silenced for various MAPKs, MAPKKs, and MAPKKKs, those in which GmMAPK4 homologs (GmMPK4s) were silenced 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) signaling pathways, were significantly up-regulated in GmMPK4-silenced plants, whereas 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 hydrogen peroxide accumulation was significantly increased in GmMPK4-silenced plants. Accordingly, GmMPK4-silenced plants were more resistant to downy mildew and Soybean mosaic virus compared with vector control plants. Using bimolecular fluorescence complementation analysis and in vitro kinase assays, we determined that GmMKK1 and GmMKK2 might function upstream of GmMPK4. Taken together, our results indicate that GmMPK4s negatively regulate SA accumulation and defense response but positively regulate plant growth and development, and their functions are conserved across plant species.

Oomycete Interactions with Plants: Infection Strategies and Resistance Principles

“…Silencing of Glycine max (soybean) MPK4 (GmMPK4) leads to enhanced resistance to the downy mildew Peronospora manshurica (109). Suggestions have been made that GmMPK4 silencing causes increased lignin biosynthesis, which may indirectly provide a physical barrier at the epidermal cells, such that the oomycete cannot penetrate into the mesophyll.…”

Evolutionary history of mitogen-activated protein kinase (MAPK) genes inLotus,Medicago, andPhaseolus

“…29 One of the well-studied MAPKs in legumes is MAPK4 ortholog in soybean: this gene is involved in negative regulation of defense mechanism while in positive regulation of growth and development. 30 MAPKs in legumes are known to involve in various signaling responses that involve root organogenesis-for example, in Lupinus albus, activation of MAPKs such as SIMK and SAMK are required for infection of Bradyrhizobia sp. or other compatible microbes to establish symbiotic interactions.…”

High‐Density Mapping of Resistance QTL Toward Phytophthora sojae, Pythium irregulare, and Fusarium graminearum in the Same Soybean Population

“…irregulare and F. graminearum compared with P. sojae. Many of these belonged to families that have previously been implicated in defense, such as WRKY transcription factors (Yin et al, 2013), which have previously been shown to be involved in the salicylic acid defense pathway and in salicylic acid-jasmonic acid cross talk both in Arabidopsis and in soybean (Euglem and Somssich, 2007;Liu et al, 2011). MYB transcription factors have also been shown to play a role in defense against the soybean rust pathogen Phakopsora pachyrhizi Syd.…”