Plants and animals employ innate immune systems to cope with microbial infection. Pattern-triggered immunity relies on the recognition of microbe-derived patterns by pattern recognition receptors (PRRs). Necrosis and ethylene-inducing peptide 1-like proteins (NLPs) constitute plant immunogenic patterns that are unique, as these proteins are produced by multiple prokaryotic (bacterial) and eukaryotic (fungal, oomycete) species. Here we show that the leucine-rich repeat receptor protein (LRR-RP) RLP23 binds in vivo to a conserved 20-amino-acid fragment found in most NLPs (nlp20), thereby mediating immune activation in Arabidopsis thaliana. RLP23 forms a constitutive, ligand-independent complex with the LRR receptor kinase (LRR-RK) SOBIR1 (Suppressor of Brassinosteroid insensitive 1 (BRI1)-associated kinase (BAK1)-interacting receptor kinase 1), and recruits a second LRR-RK, BAK1, into a tripartite complex upon ligand binding. Stable, ectopic expression of RLP23 in potato (Solanum tuberosum) confers nlp20 pattern recognition and enhanced immunity to destructive oomycete and fungal plant pathogens, such as Phytophthora infestans and Sclerotinia sclerotiorum. PRRs that recognize widespread microbial patterns might be particularly suited for engineering immunity in crop plants.

Summary1. The role of energy in ecological processes has hitherto been considered primarily from the standpoint that energy supply is limited. That is, traditional resource-based ecological and evolutionary theories and the recent 'metabolic theory of ecology' (MTE) all assume that energetic constraints operate on the supply side of the energy balance equation. 2. For endothermic animals, we provide evidence suggesting that an upper boundary on total energy expenditure is imposed by the maximal capacity to dissipate body heat and therefore avoid the detrimental consequences of hyperthermia -the heat dissipation limit (HDL) theory. We contend that the HDL is a major constraint operating on the expenditure side of the energy balance equation, and that processes that generate heat compete and trade-off within a total boundary defined by heat dissipation capacity, rather than competing for limited energy supply. 3. The HDL theory predicts that daily energy expenditure should scale in relation to body mass (M b ) with an exponent of about 0AE63. This contrasts the prediction of the MTE of an exponent of 0AE75. 4. We compiled empirical data on field metabolic rate (FMR) measured by the doubly-labelled water method, and found that they scale to M b with exponents of 0AE647 in mammals and 0AE658 in birds, not significantly different from the HDL prediction (P > 0AE05) but lower than predicted by the MTE (P < 0AE001). The same statistical result was obtained using phylogenetically independent contrasts analysis. Quantitative predictions of the model matched the empirical data for both mammals and birds. There was no indication of curvature in the relationship between Log e FMR and Log e M b . 5. Together, these data provide strong support for the HDL theory and allow us to reject the MTE, at least when applied to endothermic animals. 6. The HDL theory provides a novel conceptual framework that demands a reframing of our views of the interplay between energy and the environment in endothermic animals, and provides many new interpretations of ecological and evolutionary phenomena.

Plasma membrane-borne pattern recognition receptors, which recognize microbe-associated molecular patterns and endogenous damage-associated molecular patterns, provide the first line of defense in innate immunity. In plants, leucine-rich repeat receptor kinases fulfill this role, as exemplified by FLS2 and EFR, the receptors for the microbe-associated molecular patterns flagellin and elongation factor Tu. Here we examined the perception of the damage-associated molecular pattern peptide 1 (AtPep1), an endogenous peptide of Arabidopsis identified earlier and shown to be perceived by the leucine-rich repeat protein kinase PEPR1. Using seedling growth inhibition, elicitation of an oxidative burst and induction of ethylene biosynthesis, we show that wild type plants and the pepr1 and pepr2 mutants, affected in PEPR1 and in its homologue PEPR2, are sensitive to AtPep1, but that the double mutant pepr1/pepr2 is completely insensitive. As a central body of our study, we provide electrophysiological evidence that at the level of the plasma membrane, AtPep1 triggers a receptor-dependent transient depolarization through activation of plasma membrane anion channels, and that this effect is absent in the double mutant pepr1/pepr2. The double mutant also fails to respond to AtPep2 and AtPep3, two distant homologues of AtPep1 on the basis of homology screening, implying that the PEPR1 and PEPR2 are responsible for their perception too. Our findings provide a basic framework to study the biological role of AtPep1-related danger signals and their cognate receptors.In plant immunity, a first line of defense is based on the perception of a group of conserved, pathogen-derived molecules, called microbe-associated molecular patterns (MAMPs) 4 by pattern recognition receptors, which cause the expression of defense genes as well as metabolic rearrangements, and ultimately activate basal resistance to potential pathogens (1, 2). In Arabidopsis, the best studied MAMPs are the bacterial flagellin (active epitope flg22) and elongation factor Tu (active EF-Tu epitopes elf13, elf18, and elf26), which are recognized by their cognate leucine rich repeat-receptor-like kinases FLS2 (flagellin-sensitive 2) and EFR (EF-Tu receptor), respectively (reviewed in Ref. 1). Perception of these MAMPs leads to a set of responses that can be used to monitor the recognition process, including the triggering of ion fluxes, the generation of reactive oxygen species (ROS), accumulation of ethylene, and finally up-regulation of defense-related genes; investment into increased resistance against bacterial pathogens negatively feeds back on plant growth (3). In addition to these MAMP/ pattern recognition receptor systems, another class of surveillance system recognizes plant-derived molecules previously known as "endogenous elicitors" and now as DAMPs (damageassociated molecular patterns): DAMPs are endogenous molecules that newly appear in the intercellular space in response to the damage caused by a pathogen attack, e.g. cell wall fragments or effectors deri...

SummaryThe GA 1 gene of Arabidopsis thaliana encodes ent.kaurene synthase A (KSA), which catalyzes the first committed step in the biosynthetic pathway of the plant hormone gibberellin (GA). Its location in the GA biosynthetic pathway has led to speculation that KSA regulation is one of the controlling steps. However, because KSA activity is so low that it is only measurable in Arabidopsis siliques, GA1 promoter-GUS reporter gene fusions and quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) were used to examine the expression pattern of GAl. The results from this study indicate that GA 1 gene expression is highly regulated during growth and development, and it is restricted to specific cell types at the sites of expression. GA1 promoter activity is highest in rapidly growing tissues, e.g. shoot apices, root tips, developing flowers and seeds. It is also active in the vascular tissue of some non-growing organs, such as expanded leaves, suggesting that these leaves may be a site of GA synthesis for transport to other organs. It was also found that the first one or two introns in the GA1 gene are required for proper expression. Because of the high degree of regulation, GA1 may act as a gatekeeper, controlling the flow of metabolites into the GA biosynthetic pathway, while the levels of specific bioactive GAs are controlled by other downstream steps.

SUMMARYThe perception of microbes by plants involves highly conserved molecular signatures that are absent from the host and that are collectively referred to as microbe-associated molecular patterns (MAMPs). The Arabidopsis pattern recognition receptors FLAGELLIN-SENSING 2 (FLS2) and EF-Tu receptor (EFR) represent genetically well studied paradigms that mediate defense against bacterial pathogens. Stimulation of these receptors through their cognate ligands, bacterial flagellin or bacterial elongation factor Tu, leads to a defense response and ultimately to increased resistance. However, little is known about the early signaling pathway of these receptors. Here, we characterize this early response in situ, using an electrophysiological approach. In line with a release of negatively charged molecules, voltage recordings of microelectrode-impaled mesophyll cells and root hairs of Col-0 Arabidopsis plants revealed rapid, dose-dependent membrane potential depolarizations in response to either flg22 or elf18. Using ion-selective microelectrodes, pronounced anion currents were recorded upon application of flg22 and elf18, indicating that the signaling cascades initiated by each of the two receptors converge on the same plasma membrane ion channels. Combined calcium imaging and electrophysiological measurements revealed that the depolarization was superimposed by an increase in cytosolic calcium that was indispensable for depolarization. NADPH oxidase mutants were still depolarized upon elicitor stimulation, suggesting a reactive oxygen species-independent membrane potential response. Furthermore, electrical signaling in response to either flg22 or elf 18 critically depends on the activity of the FLS2-associated receptor-like kinase BAK1, suggesting that activation of FLS2 and EFR lead to BAK1-dependent, calcium-associated plasma membrane anion channel opening as an initial step in the pathogen defense pathway.

Basal metabolic rate (BMR) was established as a common reference point allowing comparable measures across different individuals and species. BMR is often regarded as a minimal rate of metabolism compatible with basic processes necessary to sustain life. One confusing aspect, however, is that BMR is highly variable, both within and between species. A potential explanation for this variability is that while individuals with high BMRs may suffer the disadvantage of having to feed for longer to cover the extra energy demands, this may be offset by advantages that accrue because of the high metabolic rate. One suggested advantage is that high levels of BMR are a consequence of maintaining a morphology that permits high rates of the maximal sustained rate of metabolism (SusMR)--the rate of metabolism that can be sustained for days or weeks. We have been studying the energetics of MF1 laboratory mice during peak lactation to investigate this idea. In this article, we review some of our work in connection with three particular predictions that derive from the hypothesised links among morphology, basal metabolism, and sustained metabolic rate. By comparing groups of individuals, for example, lactating and nonlactating individuals, the patterns that emerge are broadly consistent with the hypothesis that BMR and SusMR are linked by morphology. Lactating mice have bigger organs connected with energy acquisition and utilisation, greater resting metabolic rates in the thermoneutral zone, called RMRt (approximately equivalent to BMR), and high sustainable rates of maximal energy intake. However, when attempts are made to establish these relationships across individuals within lactating mice, the associations that are anticipated are either absent or very weak and depend on shared variation due to body mass. At this level there is very little support for the suggestion that variation in RMRt (and thus BMR) is sustained by associations with SusMR.

Methionine restriction (MR) decreases body weight and adiposity and improves glucose homeostasis in rodents. Similar to caloric restriction, MR extends lifespan, but is accompanied by increased food intake and energy expenditure. Most studies have examined MR in young animals; therefore, the aim of this study was to investigate the ability of MR to reverse age-induced obesity and insulin resistance in adult animals. Male C57BL/6J mice aged 2 and 12 months old were fed MR (0.172% methionine) or control diet (0.86% methionine) for 8 weeks or 48 h. Food intake and whole-body physiology were assessed and serum/tissues analyzed biochemically. Methionine restriction in 12-month-old mice completely reversed age-induced alterations in body weight, adiposity, physical activity, and glucose tolerance to the levels measured in healthy 2-month-old control-fed mice. This was despite a significant increase in food intake in 12-month-old MR-fed mice. Methionine restriction decreased hepatic lipogenic gene expression and caused a remodeling of lipid metabolism in white adipose tissue, alongside increased insulin-induced phosphorylation of the insulin receptor (IR) and Akt in peripheral tissues. Mice restricted of methionine exhibited increased circulating and hepatic gene expression levels of FGF21, phosphorylation of eIF2a, and expression of ATF4, with a concomitant decrease in IRE1α phosphorylation. Short-term 48-h MR treatment increased hepatic FGF21 expression/secretion and insulin signaling and improved whole-body glucose homeostasis without affecting body weight. Our findings suggest that MR feeding can reverse the negative effects of aging on body mass, adiposity, and insulin resistance through an FGF21 mechanism. These findings implicate MR dietary intervention as a viable therapy for age-induced metabolic syndrome in adult humans.

Several lines of evidence indicate that animals in the wild may be limited in their maximal rates of energy intake by their intrinsic physiology rather than food availability. Understanding the limits to sustained energy intake is important because this defines an envelope within which animals must trade-off competing activities. In the first part of this review, we consider the initial ideas that propelled this area and experimental evidence connected with them. An early conceptual advance in this field was the idea that energy intake could be centrally limited by aspects of the digestive process, or peripherally limited at the sites of energy utilisation. A model system that has been widely employed to explore these ideas is lactation in small rodents. Initial studies in the late 1980s indicated that energy intake might be centrally limited, but work by Hammond and colleagues in the 1990s suggested that it was more likely that the limits were imposed by capacity of the mammary glands, and other works tended to support this view. This consensus, however, was undermined by studies that showed milk production was higher in mice at low temperatures, suggesting that the capacity of the mammary gland is not a limiting factor. In the second part of the review we consider some additional hypotheses that might explain these conflicting data. These include the heat dissipation limits hypothesis, the seasonal investment hypothesis and the saturated neural control hypothesis. Current evidence with respect to these hypotheses is also reviewed. The limited evidence presently available does not unambiguously support any one of them.