Preparation of polygalacturonic acid (PGA) to study virulence in Erwinia/Pectobacterium v1

This medium is used for the growth of Erwinia/Pectobacterium species to ensure that virulence genes are turned ON. These bacteria turn on virulence (plant cell-wall degrading enzymes = PCWDEs) in response to various environmental signals. One of these signals is of plant origin, and it is thought to allow the bacterium to determine whether it has located a potential plant host. These plant signals are sensed by the bacterial sensor/regulator KdgR.

Plant Holobiont Theory: The Phytomicrobiome Plays a Central Role in Evolution and Success

Under natural conditions, plants are always associated with a well-orchestrated community of microbes—the phytomicrobiome. The nature and degree of microbial effect on the plant host can be positive, neutral, or negative, and depends largely on the environment. The phytomicrobiome is integral for plant growth and function; microbes play a key role in plant nutrient acquisition, biotic and abiotic stress management, physiology regulation through microbe-to-plant signals, and growth regulation via the production of phytohormones. Relationships between the plant and phytomicrobiome members vary in intimacy, ranging from casual associations between roots and the rhizosphere microbial community, to endophytes that live between plant cells, to the endosymbiosis of microbes by the plant cell resulting in mitochondria and chloroplasts. If we consider these key organelles to also be members of the phytomicrobiome, how do we distinguish between the two? If we accept the mitochondria and chloroplasts as both members of the phytomicrobiome and the plant (entrained microbes), the influence of microbes on the evolution of plants becomes so profound that without microbes, the concept of the “plant” is not viable. This paper argues that the holobiont concept should take greater precedence in the plant sciences when referring to a host and its associated microbial community. The inclusivity of this concept accounts for the ambiguous nature of the entrained microbes and the wide range of functions played by the phytomicrobiome in plant holobiont homeostasis.

The Ecology of Salicylic Acid Signaling: Primary, Secondary and Tertiary Effects with Applications in Agriculture

The salicylic acid pathway is one of the primary plant defense pathways, is ubiquitous in vascular plants, and plays a role in rapid adaptions to dynamic abiotic and biotic stress. Its prominence and ubiquity make it uniquely suited for understanding how biochemistry within plants can mediate ecological consequences. Induction of the salicylic acid pathway has primary effects on the plant in which it is induced resulting in genetic, metabolomic, and physiologic changes as the plant adapts to challenges. These primary effects can in turn have secondary consequences for herbivores and pathogens attacking the plant. These secondary effects can both directly influence plant attackers and mediate indirect interactions between herbivores and pathogens. Additionally, stimulation of salicylic acid related defenses can affect natural enemies, predators and parasitoids, which can recruit to plant signals with consequences for herbivore populations and plant herbivory aboveground and belowground. These primary, secondary, and tertiary ecological consequences of salicylic acid signaling hold great promise for application in agricultural systems in developing sustainable high-yielding management practices that adapt to changing abiotic and biotic environments.

Chemoperception of Specific Amino Acids Controls Phytopathogenicity in Pseudomonas syringae pv. tomato

ABSTRACT Chemotaxis has been associated with the pathogenicity of bacteria in plants and was found to facilitate bacterial entry through stomata and wounds. However, knowledge regarding the plant signals involved in this process is scarce. We have addressed this issue using Pseudomonas syringae pv. tomato, which is a foliar pathogen that causes bacterial speck in tomato. We show that the chemoreceptor P. syringae pv. tomato PscA (PsPto-PscA) recognizes specifically and with high affinity l-Asp, l-Glu, and d-Asp. The mutation of the chemoreceptor gene largely reduced chemotaxis to these ligands but also altered cyclic di-GMP (c-di-GMP) levels, biofilm formation, and motility, pointing to cross talk between different chemosensory pathways. Furthermore, the PsPto-PscA mutant strain showed reduced virulence in tomato. Asp and Glu are the most abundant amino acids in plants and in particular in tomato apoplasts, and we hypothesize that this receptor may have evolved to specifically recognize these compounds to facilitate bacterial entry into the plant. Infection assays with the wild-type strain showed that the presence of saturating concentrations of d-Asp also reduced bacterial virulence. IMPORTANCE There is substantive evidence that chemotaxis is a key requisite for efficient pathogenesis in plant pathogens. However, information regarding particular bacterial chemoreceptors and the specific plant signal that they sense is scarce. Our work shows that the phytopathogenic bacterium Pseudomonas syringae pv. tomato mediates not only chemotaxis but also the control of pathogenicity through the perception of the plant abundant amino acids Asp and Glu. We describe the specificity of the perception of l- and d-Asp and l-Glu by the PsPto-PscA chemoreceptor and the involvement of this perception in the regulation of pathogenicity-related traits. Moreover, a saturating concentration of d-Asp reduces bacterial virulence, and we therefore propose that ligand-mediated interference of key chemoreceptors may be an alternative strategy to control virulence.

Gasotransmitters in Action: Nitric Oxide-Ethylene Crosstalk during Plant Growth and Abiotic Stress Responses

Since their first description as atmospheric gases, it turned out that both nitric oxide (NO) and ethylene (ET) are multifunctional plant signals. ET and polyamines (PAs) use the same precursor for their synthesis, and NO can be produced from PA oxidation. Therefore, an indirect metabolic link between NO and ET synthesis can be considered. NO signal is perceived primarily through S-nitrosation without the involvement of a specific receptor, while ET signal is sensed by a well-characterized receptor complex. Both NO and ET are synthetized by plants at various developmental stages (e.g., seeds, fruits) and as a response to numerous environmental factors (e.g., heat, heavy metals) and they mutually regulate each other’s levels. Most of the growth and developmental processes (e.g., fruit ripening, de-etiolation) are regulated by NO–ET antagonism, while in abiotic stress responses, both antagonistic (e.g., dark-induced stomatal opening, cadmium-induced cell death) and synergistic (e.g., UV-B-induced stomatal closure, iron deficiency-induced expression of iron acquisition genes) NO–ET interplays have been revealed. Despite the numerous pieces of experimental evidence revealing NO–ET relationships in plants, the picture is far from complete. Understanding the mechanisms of NO–ET interactions may contribute to the increment of yield and intensification of stress tolerance of crop plants in changing environments.

Colletotrichum orbiculare MTF4 Is a Key Transcription Factor Downstream of MOR Essential for Plant Signal-Dependent Appressorium Development and Pathogenesis

The cucumber anthracnose fungus Colletotrichum orbiculare forms a specialized infection structure, called an appressorium. Appressorium differentiation relies on fungal perception of physical and biochemical signals at the plant surface. Our previous report showed that the morphogenesis-related NDR (nuclear Dbf2-related) kinase pathway (MOR) is crucial for translating plant-derived signals for appressorium development. Here, we focused on identifying transcriptional regulators downstream of MOR that are involved in plant signal sensing and transduction for appressorium development. Based on whole-genome transcript profiling, we identified a Zn(II)2Cys6 transcription factor, CoMTF4, as a potential downstream factor of MOR. CoMTF4 was expressed in planta rather than in vitro under the control of the NDR kinase CoCbk1. Phenotypes of comtf4 mutants, strains with constitutively active CoCbk1 and strains with constitutive overexpression of CoMTF4 suggested that CoMtf4 acts downstream of MOR. Furthermore, nuclear localization of CoMtf4 was dependent on the MOR and responsive to plant-derived signals that lead to appressorium morphogenesis. Thus, we conclude that CoMtf4 is a transcription factor downstream of MOR that is essential for appressorium morphogenesis and pathogenesis and is regulated in response to plant-derived signals. This study provides insights into fungal sensing of plant signals and subsequent responses critical for appressorium formation.

Study on Cycle-Based Fatigue Monitoring Technique

According to NUREG/CR-6909, the coolant environments have great influence on the fatigue resistance of the nuclear piping and equipment. As there are many conservatives in the cycle number and temperature/pressure scope of design transient, the fatigue usage factor of some main equipment may exceed the design requirement if the environmentally-assisted fatigue (EAF) is considered in the design phase. In order to solve this problem, the fatigue usage factor may be calculated by using real transient cycle and sequence based on cycle-based fatigue monitoring technique in nuclear power plant. Using this method the conservatives of design transients will be deleted and the life of main equipments should not be influenced by considering EAF. The method flow and key technologies for cycle-based fatigue monitoring technique were studied. Four steps were needed to get fatigue usage factor: transient statistics, stress reconstruction, fatigue calculation and EAF correction. Plant signals needed for the fatigue monitoring system were provided based on in service nuclear power plant. Transient statistics (include transient detection, classification and statistics) was the most important and difficulty of the four steps and it could not only benefit the fatigue life, but also can benefit the aging management, design and operating improvement. Transient statistics was done according to reactor power level, the initial state and causes of the transient, the protection actions and some of other important plant signals. According to reactor power which is the most important signal, the transient can be divided into four types: transients during reactor at no-load, full-power, power varying and reactor trip. The initial and final state of the transient and rate of change were used to classify the no-load transients. At full power state, only two transients were included. Power varying transients can be classified by initial and final power level. Reactor trip signals, pump state, pressure, temperature and other operating signals were used to classify reactor trip transients. A stress sequence was built according to transient sequence. The extremal stress of the sequence was selected and fatigue usage factor was calculated. The environmental correction factor Fen mentioned in NUREG/CR-6909 was used to modify the fatigue usage factor in order to consider the influence of EAF. The method was verified by assumption events and the result shows that the method could detect and classify operating transients accurately. The cycle-based fatigue monitoring technique should be improved by using the real plant parameters and can be programmed and used in plant fatigue monitor.