RNA–directed DNA methylation (RdDM) is an epigenetic control mechanism driven by small interfering RNAs (siRNAs) that influence gene function. In plants, little is known of the involvement of the RdDM pathway in regulating traits related to immune responses. In a genetic screen designed to reveal factors regulating immunity in Arabidopsis thaliana, we identified NRPD2 as the OVEREXPRESSOR OF CATIONIC PEROXIDASE 1 (OCP1). NRPD2 encodes the second largest subunit of the plant-specific RNA Polymerases IV and V (Pol IV and Pol V), which are crucial for the RdDM pathway. The ocp1 and nrpd2 mutants showed increases in disease susceptibility when confronted with the necrotrophic fungal pathogens Botrytis cinerea and Plectosphaerella cucumerina. Studies were extended to other mutants affected in different steps of the RdDM pathway, such as nrpd1, nrpe1, ago4, drd1, rdr2, and drm1drm2 mutants. Our results indicate that all the mutants studied, with the exception of nrpd1, phenocopy the nrpd2 mutants; and they suggest that, while Pol V complex is required for plant immunity, Pol IV appears dispensable. Moreover, Pol V defective mutants, but not Pol IV mutants, show enhanced disease resistance towards the bacterial pathogen Pseudomonas syringae DC3000. Interestingly, salicylic acid (SA)–mediated defenses effective against PsDC3000 are enhanced in Pol V defective mutants, whereas jasmonic acid (JA)–mediated defenses that protect against fungi are reduced. Chromatin immunoprecipitation analysis revealed that, through differential histone modifications, SA–related defense genes are poised for enhanced activation in Pol V defective mutants and provide clues for understanding the regulation of gene priming during defense. Our results highlight the importance of epigenetic control as an additional layer of complexity in the regulation of plant immunity and point towards multiple components of the RdDM pathway being involved in plant immunity based on genetic evidence, but whether this is a direct or indirect effect on disease-related genes is unclear.

Specific chemicals can prime the plant immune system for augmented defence. β-aminobutyric acid (BABA) is a priming agent that provides broad-spectrum disease protection. However, BABA also suppresses plant growth when applied in high doses, which has hampered its application as a crop defence activator. Here we describe a mutant of Arabidopsis thaliana that is impaired in BABA-induced disease immunity (ibi1) but hypersensitive to BABA-induced growth repression. IBI encodes an aspartyl-tRNA synthetase. Enantiomer-specific binding of R-BABA to IBI1 primed the protein for non-canonical defence signalling in the cytoplasm after pathogen attack. This priming was associated with aspartic acid accumulation and tRNA-induced phosphorylation of translation initiation factor eIF2α. However, mutation of eIF2α-phosphorylating GCN2 kinase did not affect BABA-induced immunity, but relieved BABA-induced growth repression. Hence, BABA-activated IBI1 controls plant immunity and growth via separate pathways. Our results open new opportunities to separate broad-spectrum disease resistance from the associated costs on plant growth.

In higher eukaryotes, induced resistance associates with acquisition of a priming state of the cells for a more effective activation of innate immunity; however, the nature of the components for mounting this type of immunological memory is not well known. We identified an extracellular subtilase from Arabidopsis, SBT3.3, the overexpression of which enhances innate immune responses while the loss of function compromises them. SBT3.3 expression initiates a durable autoinduction mechanism that promotes chromatin remodeling and activates a salicylic acid(SA)-dependent mechanism of priming of defense genes for amplified response. Moreover, SBT3.3 expression-sensitized plants for enhanced expression of the OXI1 kinase gene and activation of MAP kinases following pathogen attack, providing additional clues for the regulation of immune priming by SBT3.3. Conversely, in sbt3.3 mutant plants pathogen-mediated induction of SA-related defense gene expression is drastically reduced and activation of MAP kinases inhibited. Moreover, chromatin remodeling of defense-related genes normally associated with activation of an immune priming response appear inhibited in sbt3.3 plants, further indicating the importance of the extracellular SBT3.3 subtilase in the establishment of immune priming. Our results also point to an epigenetic control in the regulation of plant immunity, since SBT3.3 is up-regulated and priming activated when epigenetic control is impeded. SBT3.3 represents a new regulator of primed immunity.

SUMMARYDifferential growth from 1 to 20 weeks of age was studied on 320 rabbits from two lines (New Zealand White and California) and both sexes by means of the allometric equation log y = log a + b log x. Regression lines were fitted to the evolution of organs (blood, skin, thymus, heart–lungs, liver, kidneys and alimentary tract), carcass, tissues (bone, lean and fat) and anatomic components (head, breast and ribs, loin, abdominal wall, fore and hind legs) relative to empty body weight; stomach, caecum and intestines relative to alimentary tract; bone and lean groups relative to total bone and lean and fat depots relative to total fat.The convenience for a correct description of relative growth of determining both the quantitative growth, in order to apply the allometric equation only to the real growth period of each component, and the possible existence of allometric changes, is discussed.The results for each component are presented and discussed. There were no significant differences due to line, and sex had a significant influence (P < 0·001) only on the relative growths of total fat, lean content in the loin and hypodermic fat. All the components, with the exception only of thymus, presented a change in their allometric coefficients. These changes for most components, except fat depots, were concentrated in a small interval of time (4–8 weeks of age) between weaning and the inflexion point of the body weight growth curve.

Programmable integrated photonic circuits have been called upon to lead a new revolution in information systems by teaming up with high speed digital electronics and in this way, adding unique complementary features supported by their ability to provide bandwidth-unconstrained analog signal processing. Relying on a common hardware implemented by two-dimensional integrated photonic waveguide meshes, they can provide multiple functionalities by suitable programming of their control signals. Scalability, which is essential for increasing functional complexity and integration density, is currently limited by the need to precisely control and configure several hundreds of variables and simultaneously manage multiple configuration actions. Here we propose and experimentally demonstrate two different approaches towards management automation in programmable integrated photonic circuits. These enable the simultaneous handling of circuit self-characterization, auto-routing, self-configuration and optimization. By combining computational optimization and photonics, this work takes an important step towards the realization of high-density and complex integrated programmable photonics.

Progeny of heavily diseased plants develop transgenerational acquired resistance (TAR). In Arabidopsis, TAR can be transmitted over one stress-free generation. Although DNA methylation has been implicated in the regulation of TAR, the relationship between TAR and global DNA methylation remains unknown. Here, we characterised the methylome of TAR-expressing Arabidopsis at different generations after disease exposure. Global clustering of cytosine methylation revealed TAR-related patterns in the F3 generation, but not in the F1 generation. The majority of differentially methylated positions (DMPs) occurred at CG context in gene bodies. TAR in F3 progeny after one initial generation of disease, followed by two stress-free generations, was lower than TAR in F3 progeny after three successive generations of disease. This difference in TAR effectiveness was proportional to the intensity of differential methylation at a sub-set of cytosine positions. Comparison of TAR-related DMPs with previously characterised cytosine methylation in mutation accumulation lines revealed that ancestral disease stress preferentially acts on methylation-labile cytosine positions, but also extends to methylation-stable positions. Thus, the TAR-related impact of ancestral disease extends beyond stochastic variation in DNA methylation. Our study has shown that the Arabidopsis epigenome responds globally to disease in previous generations and we discuss its contribution to TAR.

SUMMARYWater scarcity and corresponding abiotic drought stress is one of the most important factors limiting plant performance and yield. In addition, plant productivity is severely compromised worldwide by infection with microbial pathogens. Two of the most prominent pathways responsible for drought tolerance and disease resistance to fungal pathogens in Arabidopsis are those controlled by the phytohormones abscisic acid (ABA) and the oxylipin methyl jasmonate (MeJA), respectively. Here, we report on the functional characterization of OCP3, a transcriptional regulator from the homeodomain (HD) family. The Arabidopsis loss-of-function ocp3 mutant exhibits both drought resistance and enhanced disease resistance to necrotrophic fungal pathogens. Double-mutant analysis revealed that these two resistance phenotypes have different genetic requirements. Whereas drought tolerance in ocp3 is ABA-dependent but MeJA-independent, the opposite holds true for the enhanced disease resistance characteristics. These observations lead us to propose a regulatory role of OCP3 in the adaptive responses to these two stresses, functioning as a modulator of independent and specific aspects of the ABA-and MeJA-mediated signal transduction pathways.

Priming of defense increases the responsiveness of the plant immune system and can provide broad-spectrum protection against disease. Recent evidence suggests that priming of defense can be inherited epigenetically to following generations. However, the mechanisms of long-lasting defense priming within one generation remains poorly understood. Here, we have investigated the mechanistic basis of long-lasting induced resistance after treatment with β -aminobutyric acid (BABA), an agent that mimics biologically induced resistance phenomena. BABA-induced resistance (BABA-IR) is based on priming of salicylic acid (SA)-dependent and SA-independent defenses. BABA-IR could be detected up to 28 days after treatment of wild-type Arabidopsis. This long-lasting component of the induced resistance response requires the regulatory protein NPR1 and is associated with priming of SA-inducible genes. In contrast, NPR1-independent resistance by BABA was transient and had disappeared by 14 days after treatment. Chromatin immunoprecipitation (ChIP) assays revealed no increased acetylation of histone H3K9 at promoters regions of priming-responsive genes, indicating that this post-translational histone modification is not critical for long-term transcriptional priming. Interestingly, the kyp-6 mutant, which is affected in methyltransferase activity of H3K9, was blocked in long-lasting BABA-IR, indicating a critical requirement of this post-translational histone modification in long-lasting BABA-IR. Considering that KYP suppresses gene transcription through methylation of H3K9 and CpHpG DNA methylation, we propose that KYP enables long-term defense gene priming by silencing suppressor genes of SA/NPR1-dependent genes.