A rice fungal MAMP‐responsive MAPK cascade regulates metabolic flow to antimicrobial metabolite synthesis

Abstract

Plants recognize potential microbial pathogens through microbial-associated molecular patterns (MAMPs) and activate a series of defense responses, including cell death and the production of reactive oxygen species (ROS) and diverse anti-microbial secondary metabolites. Mitogen-activated protein kinase (MAPK) cascades are known to play a pivotal role in mediating MAMP signals; however, the signaling pathway from a MAPK cascade to the activation of defense responses is poorly understood. Here, we found in rice that the chitin elicitor, a fungal MAMP, activates two rice MAPKs (OsMPK3 and OsMPK6) and one MAPK kinase (OsMKK4). OsMPK6 was essential for the chitin elicitor-induced biosynthesis of diterpenoid phytoalexins. Conditional expression of the active form of OsMKK4 (OsMKK4DD) induced extensive alterations in gene expression, which implied dynamic changes of metabolic flow from glycolysis to secondary metabolite biosynthesis while suppressing basic cellular activities such as translation and cell division. OsMKK4DD also induced various defense responses, such as cell death, biosynthesis of diterpenoid phytoalexins and lignin but not generation of extracellular ROS. OsMKK4DD-induced cell death and expression of diterpenoid phytoalexin pathway genes, but not that of phenylpropanoid pathway genes, were dependent on OsMPK6. Collectively, the OsMKK4–OsMPK6 cascade plays a crucial role in reprogramming plant metabolism during MAMP-triggered defense responses.

SALT-RESPONSIVE ERF1 Regulates Reactive Oxygen Species-Dependent Signaling during the Initial Response to Salt Stress in Rice

“…Remarkably, several TF and MAPK cascade genes acting downstream of SERF1 are activated upon induced expression of MKK4 DD in rice protoplasts, including DREB2A, ZFP179, MAP3K6, and MAPK5 (Kishi- Kaboshi et al, 2010). In addition, it was demonstrated that MAPK5 is phosphorylated by MKK4 (Kishi-Kaboshi et al, 2010), suggesting that SERF1 acts not only upstream but also downstream of a salt-responsive MAPK cascade.…”

“…In addition, it was demonstrated that MAPK5 is phosphorylated by MKK4 (Kishi-Kaboshi et al, 2010), suggesting that SERF1 acts not only upstream but also downstream of a salt-responsive MAPK cascade. Because in wild-type plants, all direct SERF1 targets are induced within 30 min of salt stress (Figure 4), well before the maximum induction of SERF1 ( Figure 1A), it is likely that the early activation of target genes during salt stress does not exclusively occur through the de novo protein synthesis of SERF1 but also by an already present SERF1 protein, which is activated upon salt stress.…”

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

“…2, 4,205 and 5,267 probe sets were induced and repressed, respectively, in GmMPK4-silenced plants, demonstrating that a massive transcriptome reprogramming occurred. Such altered mRNA transcript profiles were not unexpected, because similar dramatic transcriptome changes have been previously shown in rice plants overexpressing OsMKK4 DD (Kishi-Kaboshi et al, 2010). Because of the extensive changes in gene expression, we analyzed the expression of 48 rRNA soybean probe sets and found that only one rRNA gene was identified as differentially expressed between vector control and GmMPK4-silenced plants (soybean_rRNA_1692_RC_at; P = 0.00085, q = 0.003; Supplemental Table S2).…”

Plant Innate Immune Response: Qualitative and Quantitative Resistance

“…MPK4 phosphorylation upon Pseudomonas syringae infection of Arabidopsis, released MKS1 and WRKY33, which induced the biosynthesis of camalexin (Rushton et al, 2010). In rice, OsMKK4-OsMPK4/MPK6 play crucial roles in regulating the biosynthesis of diterpenoid-and phenylpropanoid-derived phytoalexins and also lignins in response to a fungal chitin elicitor of M. oryzae (KishiÀKaboshi et al, 2010). In maize following Fusarium verticillioides infection, brassinosteroid-insensitive-1-associated receptor kinase 1 (BAK1) and homologs of AtMKK4 were associated with ear rot resistance (Lanubile et al, 2014).…”