Plants have evolved elaborate mechanisms to perceive and integrate signals from various environmental conditions. On leaf surface, stomata formed by pairs of guard cells mediate gas exchange, water transpiration as well as function in response to abiotic and biotic stresses. Stomatal closure could be induced by drought, salt, pathogen and other adverse conditions. This constitutes an instant defense response to prevent further damage to plants. Abscisic acid (ABA) is a major plant hormone involved in stress responses. Stress-activated ABA synthesis causes stomatal closure and prevents opening to reduce water loss and cell dehydration. Key regulatory receptor complex and other important components in the ABA signaling pathway have been identified. However, our knowledge of ABA signal transduction in guard cells is far from complete. Jasmonates are a group of phytohormones generally known to be important for plant defense against insects and necrotrophic pathogens. The increased levels of methyl jasmonate (MeJA) induced by herbivory and pathogen invasion show a similar effect on stomatal movement associated with ROS production as ABA. Investigation of guard cell signaling networks involving the two important phytohormones is significant and exciting. Information about protein and metabolite components and how they interact in guard cells is lacking. Here we review recent advances on hormone signaling networks in guard cells and how the networks integrate environmental signals to plant physiological output.

Studies related to the functional and regulatory aspects of proteolytic processing are of interest to cell biologists, developmental biologists and investigators who work on human diseases. Much of what is known about this topic derives from the study of the proteolytic processing of the amyloid precursor protein (APP), which is involved in the pathology of Alzheimer’s disease, and of the Notch protein and its Delta ligand, which play roles during embryonic development and in biologic processes in the adult. The proteolytic processing of plasma membrane receptor proteins is under the control of different enzymes that are responsible for releasing the ectodomain into the extracellular environment, where it has the potential to function as a signaling molecule and/or regulate the availability of the receptor’s ligand. Following shedding of the ectodomain, the γ-secretase enzymatic complex cleaves the transmembrane domain and releases the cytoplasmic domain (ICD) of the receptor. The ICD can function in the cytoplasm and/or at the nucleus.

Members of the low-density lipoprotein receptor (LDLR) family are endocytic-signaling proteins that perform a wide variety of physiologic functions during development and in the adult life. In addition these receptors have been implicated in a variety of diseases in adults. The prototypic receptor for this family of proteins is the LDLR itself. Besides their binding to apolipoproteins, these receptors bind many ligands that are destined for internalization and degradation. Some ligands have signaling properties. The proteolytic processing of certain members of the LDLR family not only controls receptor availability at the cell surface but also has functional consequences that amplify the spectrum of roles that these receptors perform. In addition, many complex regulatory mechanisms control the proteolytic processing of these receptors.

The indeterminate growth pattern displayed by shoots is mediated by the proper maintenance of the shoot meristem. Meristem maintenance is dependent upon the balance of stem cell perpetuation in the central zone (CZ) and organogenesis in the peripheral zone (PZ). Although the mechanisms that coordinate CZ and PZ function is not understood, meristem cell fate is likely achieved by the spatial interplay between gene regulatory networks and hormone signaling pathways. During shoot maturation, the identity of the shoot meristem as well as the lateral organs are transformed during the vegetative and reproductive transitions. Studies in model plant systems indicate that three amino acid extension (TALE) homeodomain proteins integrate signaling events that transform the identity of the shoot meristem and establish reproductive patterns of growth. This review will highlight the function of TALE homeodomain transcription factors that regulate shoot meristem cell fate and also function with phase specific regulators to maintain shoot meristem identity.

Plants have evolved multiple layers of defense against various pathogens in the environment. Receptor-like kinases/proteins (RLKs/RLPs) are on the front lines of the battle between plants and pathogens since they are present at the plasma membrane and perceive signature molecules from either the invading pathogen or damaged plant tissue. With a few notable exceptions, most RLKs/RLPs are positive regulators of plant innate immunity. In this review, we summarize recently discovered RLKs/RLPs that are involved in plant defense responses against various classes of pathogens. We also describe what is currently known about the mechanisms of RLK-mediated initiation of signaling via protein-protein interactions and phosphorylation.

Enterococcus faecalis and Enterococcus faecium are both human intestinal colonizers frequently used in medical bacteriology teaching laboratories in order to train students in bacterial identification. In addition, hospitals within the United States and around the world commonly isolate these bacteria because they are a cause of bacteremia, urinary tract infections, endocarditis, wound infections, and nosocomial infections. Given that enterococci are becoming more of a world health hazard, it is important for laboratories to be able to distinguish these bacteria within hospitalized patients from other bacterial genera. In addition, laboratories must differentiate different species within the Enterococcus genus as well as different strains within each species. Though enterococci are differentiated from other bacterial genera via classical culture and biochemical methods, nucleic acid sequencing is required to differentiate species within the genus—a costly, time consuming, and technically challenging procedure for laboratory technicians that, in itself, does not necessarily lead to speedy identification of bactericidal antibiotics. In this study, we perform antibiogram analysis to show (1) that penicillin can be rapidly employed to distinguish strains and clinical isolates of E. faecalis from E. faecium, (2) E. faecalis is susceptible to ampicillin, and (3) that vancomycin resistance in enterococci shows no sign of abating. Additionally, we show that E. faecalis can grow on mannitol salt agar and ferment mannitol, while E. faecium lacks these phenotypes. These data reveal that we now have rapid, cost effective ways to identify enterococci to the species, and not just genus, level and have significance for patient treatment in hospitals.