An evolutionarily young defense metabolite influences the root growth of plants via the ancient TOR signaling pathway.

To optimize fitness a plant should monitor its metabolism to appropriately control growth and defense. Primary metabolism can be measured by the universally conserved TOR (Target of Rapamycin) pathway to balance growth and development with the available energy and nutrients. Recent work suggests that plants may measure defense metabolites to potentially provide a strategy ensuring fast reallocation of resources to coordinate plant growth and defense. There is little understanding of mechanisms enabling defense metabolite signaling. To identify mechanisms of defense metabolite signaling, we used glucosinolates, an important class of plant defense metabolites. We report novel signaling properties specific to one distinct glucosinolate, 3-hydroxypropylglucosinolate across plants and fungi. This defense metabolite, or derived compounds, reversibly inhibits root growth and development. 3-hydroxypropylglucosinolate signaling functions via genes in the ancient TOR pathway. If this event is not unique, this raises the possibility that other evolutionarily new plant metabolites may link to ancient signaling pathways

Coronatine-insensitive 1 (COI1) mediates transcriptional responses of <i>Arabidopsis thaliana</i> to external potassium supply

The ability to adjust growth and development to the availability of mineral nutrients in the soil is an essential life skill of plants but the underlying signaling pathways are poorly understood. In &lt;i&gt;Arabidopsis thaliana&lt;/i&gt;, shortage of potassium (K) induces a number of genes related to the phytohormone jasmonic acid (JA). Using comparative microarray analysis of wild-type and coi1-16 mutant plants, we classified transcriptional responses to K with respect to their dependence on COI1, a central component of oxylipin signaling. Expression profiles obtained in a short-term experiment clearly distinguished between COI1-dependent and COI1-independent K-responsive genes, and identified both known and novel targets of JA-COI1-signaling. During long-term K-deficiency, coi-16 mutants displayed de novo responses covering similar functions as COI1-targets except for defense. A putative role of JA for enhancing the defense potential of K-deficient plants was further supported by the observation that plants grown on low K were less damaged by thrips than plants grown with sufficient K

Making sense o fhormone-mediated defense networking: from rice to Arabidopsis

Phytohormones are not only essential for plant growth and development but also play central roles in triggering the plant immune signaling network. Historically, research aimed at elucidating the defense-associated role of hormones has tended to focus on the use of experimentally tractable dicot plants such as Arabidopsis thaliana. Emerging from these studies is a picture whereby complex crosstalk and induced hormonal changes mold plant health and disease, with outcomes largely dependent on the lifestyle and infection strategy of invading pathogens. However, recent studies in monocot plants are starting to provide additional important insights into the immune-regulatory roles of hormones, often revealing unique complexities. In this review, we address the latest discoveries dealing with hormone-mediated immunity in rice, one of the most important food crops and an excellent model for molecular genetic studies in monocots. Moreover, we highlight interactions between hormone signaling, rice defense and pathogen virulence, and discuss the differences and similarities with findings in Arabidopsis. Finally, we present a model for hormone defense networking in rice and describe how detailed knowledge of hormone crosstalk mechanisms can be used for engineering durable rice disease resistance

Interaction points in plant stress signaling pathways

Special Issue: 70 years of SPPS – Outlook by Early-Career PIsPlants live in a world where they are challenged by abiotic and biotic stresses. In response to unfavorable conditions or an acute challenge like a pathogen attack, plants use various signaling pathways that regulate expression of defense genes and other mechanisms to provide resistance or stress adaptation. Identification of the regulatory steps in defense signaling has seen much progress in recent years. Many of the identified signaling pathways show interactions with each other, exemplified by the modulation of the jasmonic acid response by salicylic acid. Accordingly, defense regulation is more appropriately thought of as a web of interactions, rather than linear pathways. Here we describe various regulatory components and how they interact to provide an appropriate defense response. One of the common assays to monitor the output of defense signaling, as well as interaction between signaling pathways, is the measurement of altered gene expression. We illustrate that, while this is a suitable assay to monitor defense regulation, it can also inadvertently provide overstated conclusions about interaction among signaling pathways.Peer reviewe

Stress Marker Signatures in Lesion Mimic Single and Double Mutants Identify a Crucial Leaf Age-Dependent Salicylic Acid Related Defense Signal

Plants are exposed to abiotic and biotic stress conditions throughout their lifespans that activates various defense programs. Programmed cell death (PCD) is an extreme defense strategy the plant uses to manage unfavorable environments as well as during developmentally induced senescence. Here we investigated the role of leaf age on the regulation of defense gene expression in Arabidopsis thaliana. Two lesion mimic mutants with misregulated cell death, catalase2 (cat2) and defense no death1 (dnd1) were used together with several double mutants to dissect signaling pathways regulating defense gene expression associated with cell death and leaf age. PCD marker genes showed leaf age dependent expression, with the highest expression in old leaves. The salicylic acid (SA) biosynthesis mutant salicylic acid induction deficient2 (sid2) had reduced expression of PCD marker genes in the cat2 sid2 double mutant demonstrating the importance of SA biosynthesis in regulation of defense gene expression. While the auxin-and jasmonic acid (JA)-insensitive auxin resistant1 (axr1) double mutant cat2 axr1 also led to decreased expression of PCD markers; the expression of several marker genes for SA signaling (ISOCHORISMATE SYNTHASE 1, PR1 and PR2) were additionally decreased in cat2 axr1 compared to cat2. The reduced expression of these SA markers genes in cat2 axr1 implicates AXR1 as a regulator of SA signaling in addition to its known role in auxin and JA signaling. Overall, the current study reinforces the important role of SA signaling in regulation of leaf age-related transcript signatures.Peer reviewe

Ethylene supports colonization of plant roots by the mutualistic fungus Piriformospora indica

The mutualistic basidiomycete Piriformospora indica colonizes roots of mono- and dicotyledonous plants, and thereby improves plant health and yield. Given the capability of P. indica to colonize a broad range of hosts, it must be anticipated that the fungus has evolved efficient strategies to overcome plant immunity and to establish a proper environment for nutrient acquisition and reproduction. Global gene expression studies in barley identified various ethylene synthesis and signaling components that were differentially regulated in P. indica-colonized roots. Based on these findings we examined the impact of ethylene in the symbiotic association. The data presented here suggest that P. indica induces ethylene synthesis in barley and Arabidopsis roots during colonization. Moreover, impaired ethylene signaling resulted in reduced root colonization, Arabidopsis mutants exhibiting constitutive ethylene signaling, -synthesis or ethylene-related defense were hyper-susceptible to P. indica. Our data suggest that ethylene signaling is required for symbiotic root colonization by P. indica