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Nucleotide-binding leucine-rich repeat (NLR) proteins play critical roles in plant immunity. However, how NLRs are regulated and activate defense signaling is not fully understood. The rice (Oryza sativa) NLR receptor Piz-t confers broad-spectrum resistance to the fungal pathogen Magnaporthe oryzae and the RING-type E3 ligase AVRPIZ-T INTERACTING PROTEIN 10 (APIP10) negatively regulates Piz-t accumulation. In this study, we found that APIP10 interacts with two rice transcription factors, VASCULAR PLANT ONE-ZINC FINGER 1 (OsVOZ1) and OsVOZ2, and promotes their degradation through the 26S proteasome pathway. OsVOZ1 displays transcriptional repression activity while OsVOZ2 confers transcriptional activation activity in planta. The osvoz1 and osvoz2 single mutants display modest but opposite M. oryzae resistance in the non- Piz-t background. However, the osvoz1 osvoz2 double mutant exhibits strong dwarfism and cell death, and silencing of both genes via RNA interference also leads to dwarfism, mild cell death, and enhanced resistance to M. oryzae in the non- Piz-t background. Both OsVOZ1 and OsVOZ2 interact with Piz-t. Double silencing of OsVOZ1 and OsVOZ2 in the Piz - t background decreases Piz-t protein accumulation and transcription, reactive oxygen species-dependent cell death, and resistance to M. oryzae containing AvrPiz-t. Taken together, these results indicate that OsVOZ1 and OsVOZ2 negatively regulate basal defense but contribute positively to Piz-t-mediated immunity. The E3 ligase APIP10 interacts with transcription factors OsVOZ1 and OsVOZ2 and promotes their degradation through the 26S proteasome pathway. OsVOZ1 and OsVOZ2 function synergistically to negatively regulate basal resistance but positively contribute to the NLR Piz-t-mediated immunity to the fungal pathogen Magnaporthe oryzae. [ABSTRACT FROM AUTHOR]

The receptor protein PEX5, an important component of peroxisomes, regulates growth, development, and immunity in yeast and mammals. PEX5 also influences growth and development in plants, but whether it participates in plant immunity has remained unclear. Here, we report that knockdown of OsPEX5 enhances resistance to the rice blast fungus Magnaporthe oryzae. We demonstrate that OsPEX5 interacts with the E3 ubiquitin ligase APIP6, a positive regulator of plant immunity. APIP6 ubiquitinates OsPEX5 in vitro and promotes its degradation in vivo via the 26S proteasome pathway. In addition, OsPEX5 interacts with the aldehyde dehydrogenase OsALDH2B1, which functions in growth-defense trade-offs in rice. OsPEX5 stabilizes OsALDH2B1 to enhance its repression of the defense-related gene OsAOS2. Our study thus uncovers a previously unrecognized hierarchical regulatory mechanism in which an E3 ubiquitin ligase targets a peroxisome receptor protein that negatively regulates immunity in rice by stabilizing an aldehyde dehydrogenase that suppresses defense gene expression. [Display omitted] • OsPEX5 negatively regulates immunity in rice • OsPEX5 interacts with and is ubiquitinated by APIP6 • APIP6 positively regulates the plant response to rice blast by degrading OsPEX5 • OsPEX5 stabilizes OsALDH2B1 to increase its inhibitory effect on OsAOS2 The peroxisomal receptor protein PEX5 is a crucial component of peroxisomes. You et al. show that OsPEX5, modulated by the E3 ubiquitin ligase APIP6, negatively regulates immunity in rice. In addition, OsPEX5 interacts with and stabilizes the aldehyde dehydrogenase OsALDH2B1 to inhibit the expression of the defense gene OsAOS2. [ABSTRACT FROM AUTHOR]

Potassium (K+) is required by plants for growth and development, and also contributes to immunity against pathogens. However, it has not been established whether pathogens modulate host K+ signaling pathways to enhance virulence and subvert host immunity. Here, we show that the effector protein AvrPiz-t from the rice blast pathogen Magnaporthe oryzae targets a K+ channel to subvert plant immunity. AvrPiz-t interacts with the rice plasma-membrane-localized K+ channel protein OsAKT1 and specifically suppresses the OsAKT1-mediated K+ currents. Genetic and phenotypic analyses show that loss of OsAKT1 leads to decreased K+ content and reduced resistance against M. oryzae. Strikingly, AvrPiz-t interferes with the association of OsAKT1 with its upstream regulator, the cytoplasmic kinase OsCIPK23, which also plays a positive role in K+ absorption and resistance to M. oryzae. Furthermore, we show a direct correlation between blast disease resistance and external K+ status in rice plants. Together, our data present a novel mechanism by which a pathogen suppresses plant host immunity by modulating a host K+ channel. [ABSTRACT FROM AUTHOR]

[Display omitted] Phenolamides (PAs), a diverse group of specialized metabolites, including hydroxycinnamoylputrescine (HP), hydroxycinnamoylagmatine, and hydroxycinnamoyltryptamine, are important in plant resistance to biotic stress. However, the genes involved in the biosynthesis and modulation of PAs have not been fully elucidated. This study identified an HP biosynthetic gene cluster in rice (Oryza sativa) comprising one gene (OsODC) encoding a decarboxylase and two tandem-duplicated genes (OsPHT3 and OsPHT4) encoding putrescine hydroxycinnamoyl acyltransferases coexpressed in different tissues. OsODC catalyzes the conversion of ornithine to putrescine, which is used in HP biosynthesis involving OsPHT3 and OsPHT4. OsPHT3 or OsPHT4 overexpression causes HP accumulation and cell death and putrescine hydroxycinnamoyl acyltransferases (PHT) activity-dependent resistance against the fungal pathogen Magnaporthe oryzae. OsODC overexpression plants also confer enhanced resistance to M. oryzae. Notably, the basic leucine zipper transcription factor APIP5, a negative regulator of cell death, directly binds to the OsPHT4 promoter, repressing its transcription. Moreover, APIP5 suppression induces OsPHT4 expression and HP accumulation. Comparative genomic analysis revealed that the HP biosynthetic gene cluster is conserved in monocots. These results characterized a previously unidentified monocot-specific gene cluster that is involved in HP biosynthesis and contributes to defense and cell death in rice. [ABSTRACT FROM AUTHOR]