Molecular Pattern-triggered Immunity Research Articles

A Rice NBS-ARC Gene Conferring Quantitative Resistance to Bacterial Blight Is Regulated by a Pathogen Effector-Inducible miRNA

The bacterium Xanthomonas oryzae pv. Oryzae (Xoo) causes blight in rice worldwide, resulting in significant crop loss. However, no gene underlying a quantitative trait locus (QTL) for resistance against Xoo has been cloned yet. Here, we report the map-based cloning of a QTL, in which the NBS8R gene confers quantitative resistance to Xoo. NBS8R encodes an NB-ARC protein, which is involved in pathogen/microbe-associated molecular pattern-triggered immunity and whose expression is regulated by non-TAL effector XopQ-inducible Osa-miR1876 through DNA methylation. Sequence analysis of NBS8R in wild rice species and rice cultivars suggests that the Osa-miR1876 binding sites in the 5′ UTR of NBS8R are inserted by chance and have undergone variations with Osa-miR1876 throughout evolution. The interaction between NBS8R and XopQ-inducible Osa-miR1876 is partially in keeping with the zigzag model, revealing that quantitative genes may also follow this model to control the innate immune response or basal disease resistance, and may prove valuable in utilizing the existing landraces that harbor the NBS8R gene but with no Osa-miR1876 binding site in rice breeding for bacterial blight resistance.

Induction of in planta resistance by flagellin (Flg) and elongation factor-TU (EF-Tu) of Bacillus amyloliquefaciens (VB7) against groundnut bud necrosis virus in tomato

Role of plant growth promoting rhizobacteria (PGPR) in growth promotion and induction of resistance against various plant pathogens have been extensively studied. However, MAMP (Microbe Associated Molecular Pattern) triggered immunity (MTI) against plant viruses are not well exploited. The present study enlightens the role of two MAMP genes including, flagellin (Flg) and elongation factor (EF-Tu) in the induction of plant defense against GBNV infecting tomato. Secondary metabolites of Bacillus amyloliquefaciens (VB7), effectively suppressed GBNV symptom expression up to 84% compared to untreated control in cowpea, the indicator host plant. Agrobacterium tumefaciens EHA105 clones expressing the MAMP genes were drenched in the root zone to assess the induction of resistance against GBNV in tomato. Treatment with A. tumefaciens EHA105 clones containing flagellin (Ag- Ba.Flg) and elongation factor-TU (Ag-Ba.EF-Tu) genes as soil drench and foliar spray, reduced virus titre,0.369 OD and 0.379 OD respectively as compared to control 1.249 OD. The disease severity was reduced up to 15% in Ag-Ba.Flg treated plants compared to 88.25% in inoculated control. Further there was an increased expression of defense associated genes including, MAPKK1, WRKY33BB, NPR1 and PR1.The present investigation clearly indicated the efficiency of MAMP genes in triggering defense mechanism in tomato against GBNV.

Ca2+/Calmodulin-Dependent AtSR1/CAMTA3 Plays Critical Roles in Balancing Plant Growth and Immunity.

During plant-pathogen interactions, plants have to relocate their resources including energy to defend invading organisms; as a result, plant growth and development are usually reduced. Arabidopsis signal responsive1 (AtSR1) has been documented as a negative regulator of plant immune responses and could serve as a positive regulator of plant growth and development. However, the mechanism by which AtSR1 balances plant growth and immunity is poorly understood. Here, we performed a global gene expression profiling using Affymetrix microarrays to study how AtSR1 regulates defense- and growth-related genes in plants with and without bacterial pathogen infection. Results revealed that AtSR1 negatively regulates most of the immune-related genes involved in molecular pattern-triggered immunity (PTI), effector-triggered immunity (ETI), and in salicylic acid (SA)- and jasmonate (JA)-mediated signaling pathways. AtSR1 may rigidly regulate several steps of the SA-mediated pathway, from the activation of SA synthesis to the perception of SA signal. Furthermore, AtSR1 may also regulate plant growth through its involvement in regulating auxin- and BRs-related pathways. Although microarray data revealed that expression levels of defense-related genes induced by pathogens are higher in wild-type (WT) plants than that in atsr1 mutant plants, WT plants are more susceptible to the infection of virulent pathogen as compared to atsr1 mutant plants. These observations indicate that the AtSR1 functions in suppressing the expression of genes induced by pathogen attack and contributes to the rapid establishment of resistance in WT background. Results of electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation (ChIP)-PCR assays suggest that AtSR1 acts as transcription factor in balancing plant growth and immunity, through interaction with the “CGCG” containing CG-box in the promotors of its target genes.

Identification of Quantitative Trait Loci Controlling Gene Expression during the Innate Immunity Response of Soybean

Microbe-associated molecular pattern-triggered immunity (MTI) is an important component of the plant innate immunity response to invading pathogens. However, most of our knowledge of MTI comes from studies of model systems with relatively little work done with crop plants. In this work, we report on variation in both the microbe-associated molecular pattern-triggered oxidative burst and gene expression across four soybean (Glycine max) genotypes. Variation in MTI correlated with the level of pathogen resistance for each genotype. A quantitative trait locus analysis on these traits identified four loci that appeared to regulate gene expression during MTI in soybean. Likewise, we observed that both MTI variation and pathogen resistance were quantitatively inherited. The approach utilized in this study may have utility for identifying key resistance loci useful for developing improved soybean cultivars.