The rice Xa21 gene confers immunity to most strains of the bacterium Xanthomonas oryzae pv. oryzae (Xoo). Liquid chromatography-tandem mass spectrometry analysis of biologically active fractions from Xoo supernatants led to the identification of a 194-amino acid protein designated Ax21 (activator of XA21-mediated immunity). A sulfated, 17-amino acid synthetic peptide (axY(S)22) derived from the N-terminal region of Ax21 is sufficient for activity, whereas peptides lacking tyrosine sulfation are biologically inactive. Using coimmunoprecipitation, we found that XA21 is required for axY(S)22 binding and recognition. axY(S)22 is 100% conserved in all analyzed Xanthomonas species, confirming that Ax21 is a pathogen-associated molecular pattern and that XA21 is a pattern recognition receptor.

Rice (Oryza sativa) is a staple food for more than half the world and a model for studies of monocotyledonous species, which include cereal crops and candidate bioenergy grasses. A major limitation of crop production is imposed by a suite of abiotic and biotic stresses resulting in 30%–60% yield losses globally each year. To elucidate stress response signaling networks, we constructed an interactome of 100 proteins by yeast two-hybrid (Y2H) assays around key regulators of the rice biotic and abiotic stress responses. We validated the interactome using protein–protein interaction (PPI) assays, co-expression of transcripts, and phenotypic analyses. Using this interactome-guided prediction and phenotype validation, we identified ten novel regulators of stress tolerance, including two from protein classes not previously known to function in stress responses. Several lines of evidence support cross-talk between biotic and abiotic stress responses. The combination of focused interactome and systems analyses described here represents significant progress toward elucidating the molecular basis of traits of agronomic importance.

Acyl-homoserine lactone-mediated quorum sensing (QS) regulates diverse activities in many species of Proteobacteria. QS-controlled genes commonly code for production of secreted or excreted public goods. The acyl-homoserine lactones are synthesized by members of the LuxI signal synthase family and are detected by cognate members of the LuxR family of transcriptional regulators. QS affords a means of population density-dependent gene regulation. Control of public goods via QS provides a fitness benefit. Another potential role for QS is to anticipate overcrowding. As population density increases and stationary phase approaches, QS might induce functions important for existence in stationary phase. Here we provide evidence that in three related species of the genus Burkholderia QS allows individuals to anticipate and survive stationary-phase stress. Survival requires QS-dependent activation of cellular enzymes required for production of excreted oxalate, which serves to counteract ammonia-mediated alkaline toxicity during stationary phase. Our findings provide an example of QS serving as a means to anticipate stationary phase or life at the carrying capacity of a population by activating the expression of cytoplasmic enzymes, altering cellular metabolism, and producing a shared resource or public good, oxalate.Burkholderia carrying capacity | glumae | pseudomallei | thailandensis | cell death A cyl-homoserine lactone (AHL)-mediated quorum sensing (QS) regulates diverse activities, including bioluminescence, biofilm formation, motility, and virulence factor formation, in many Proteobacteria (1-3). AHLs are synthesized most typically by members of the LuxI family signal synthases and detected by members of the LuxR family of transcriptional regulators (1-3). A large body of work has characterized the molecular mechanisms of bacterial QS; demonstrating the population-wide benefits that drive QS-mediated cooperative behavior has proven difficult, however. Cooperative activities benefit individuals within a group (4, 5).QS-controlled genes commonly code for the production of extracellular public goods that can be shared by all members of the group regardless of which members produce them. These extracellular products are often important for nutrient acquisition, interspecies competition, or virulence (6-8). In Pseudomonas aeruginosa, QS control of secreted proteases provides fitness benefits, because the proteases are produced only when they can be used efficiently (9). Other potential roles of QS in bacteria have been proposed, including the hypothesis that QS enables bacteria to anticipate population carrying capacity in a given environment. Anticipation of stationary phase might allow individuals to modify their physiology in preparation for survival at population carrying capacity.Here we address the question of whether QS is involved in anticipation of stationary-phase stress in three closely related bacteria: the rice pathogen Burkholderia glumae, the opportunistic human pathogen Burkholderia pseudomallei, and the...

We previously characterized the rice (Oryza sativa) Submergence1 (Sub1) locus encoding three ethylene-responsive factor (ERF) transcriptional regulators. Genotypes carrying the Sub1A-1 allele are tolerant of prolonged submergence. To elucidate the mechanism of Sub1A-1-mediated tolerance, we performed transcriptome analyses comparing the temporal submergence response of Sub1A-1-containing tolerant M202(Sub1) with the intolerant isoline M202 lacking this gene. We identified 898 genes displaying Sub1A-1-dependent regulation. Integration of the expression data with publicly available metabolic pathway data identified submergence tolerance-associated pathways governing anaerobic respiration, hormone responses, and antioxidant systems. Of particular interest were a set of APETALA2 (AP2)/ERF family transcriptional regulators that are associated with the Sub1A-1-mediated response upon submergence. Visualization of expression patterns of the AP2/ERF superfamily members in a phylogenetic context resolved 12 submergence-regulated AP2/ERFs into three putative functional groups: (1) anaerobic respiration and cytokinin-mediated delay in senescence via ethylene accumulation during submergence (three ERFs); (2) negative regulation of ethylene-dependent gene expression (five ERFs); and (3) negative regulation of gibberellinmediated shoot elongation (four ERFs). These results confirm that the presence of Sub1A-1 impacts multiple pathways of response to submergence.