Most plant species are resistant to most potential pathogens. It is not known why most plant-microbe interactions do not lead to disease, although recent work indicates that this basic disease resistance is multi-factorial. Here we show that the exudation of root-derived antimicrobial metabolites by Arabidopsis thaliana confers tissue-specific resistance to a wide range of bacterial pathogens. However, a Pseudomonas syringae strain that is both at least partly resistant to these compounds and capable of blocking their synthesis/exudation is able to infect the roots and cause disease. We also show that the ability of this P. syringae strain to block antimicrobial exudation is dependent on the type III secretory system.

Landslides, floods, and droughts are recurring natural disasters in Nepal related to too much or too little water. The summer monsoon contributes more than 80% of annual rainfall, and rainfall spatial and inter-annual variation is very high. The Gandaki River, one of the three major rivers of Nepal and one of the major tributaries of the Ganges River, covers all agro-ecological zones in the central part of Nepal. Time series tests were applied for different agro-ecological zones of the Gandaki River Basin (GRB) for rainfall trends of four seasons (pre-monsoon, monsoon, post-monsoon and winter) from 1981 to 2012. OPEN ACCESSClimate 2015, 3 211The non-parametric Mann-Kendall and Sen's methods were used to determine the trends. Decadal anomalies relative to the long-term average were analyzed using the APHRODITE precipitation product. Trends in number of rainy days and timing of the monsoon were also analyzed. We found that the post-monsoon, pre-monsoon and winter rainfalls are decreasing significantly in most of the zones but monsoon rainfall is increasing throughout the basin. In the hill region, the annual rainfall is increasing but the rainy days do not show any trend. There is a tendency toward later departure of monsoon from Nepal, indicating an increase in its duration. These seasonally and topographically variable trends may have significant impacts for the agriculture and livestock smallholders that form the majority of the population in the GRB.

SUMMARYCytokinin (CK) influences many aspects of plant growth and development, and its function often involves intricate interactions with other phytohormones such as auxin and ethylene. However, the molecular mechanisms underlying the role of CK and its interactions with other growth regulators are still poorly understood. Here we describe the isolation and characterization of the Arabidopsis CK-induced root curling 1 (ckrc1) mutant. CKRC1 encodes a previously identified tryptophan aminotransferase (TAA1) involved in the indole-3-pyruvic acid (IPA) pathway of indole-3-acetic acid (IAA) biosynthesis. The ckrc1 mutant exhibits a defective root gravitropic response (GR) and an increased resistance to CK in primary root growth. These defects can be rescued by exogenous auxin or IPA. Furthermore, we show that CK up-regulates CKRC1/TAA1 expression but inhibits polar auxin transport in roots in an AHK3/ARR1/12-dependent and ethyleneindependent manner. Our results suggest that CK regulates root growth and development not only by down-regulating polar auxin transport, but also by stimulating local auxin biosynthesis.

This paper presents temporal and spatial pattern of drought phenomena in central Nepal using standardized precipitation index (SPI) at multiple time scales. The study is based on 32 years of monthly precipitation data from 40 meteorological stations from 1981 to 2012. Results indicate that, while there is no distinct trend in regional precipitation, interannual variation is large. Trend analysis of drought index shows that most stations are characterized by increases in both severity and frequency of drought and trend is stronger for longer drought time scales. Over the study period, the summer 123Nat Hazards (2016) 80:1913-1932 DOI 10.1007/s11069-015-2055 season of 2004, 2005, 2006, 2009 and winters 2006, 2008 and 2009 were the worst widespread droughts. These dry periods have a serious impact on agriculture-livestock production of central Nepal. Better understanding of these SPI dynamics could help in understanding the characteristics of droughts and also to develop effective mitigation strategies.

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Precipitation in mountain regions is often highly variable and poorly observed, limiting abilities to manage water resource challenges. Here, we evaluate remote sensing and ground station-based gridded precipitation products over Nepal against weather station precipitation observations on a monthly timescale. We find that the Tropical Rainfall Measuring Mission (TRMM) 3B-43 precipitation product exhibits little mean bias and reasonable skill in giving precipitation over Nepal. Compared to station observations, the TRMM precipitation product showed an overall Nash-Sutcliffe efficiency of 0

SummaryStaphylococcus aureus is a ubiquitous gram-positive bacterium that can cause superficial to serious systemic infections in animals and humans. Here we report the development of a plant infection model to study the pathogenesis of this bacterium. Three global regulatory mutants, RN6911 (agr) and an alpha-toxin mutant defective in biofilm formation (DU1090) which are attenuated in animal pathogenesis, were also attenuated in their ability to infect plants, suggesting that these regulators that mediate synthesis of virulence factors essential for animal pathogenesis are also required for plant pathogenesis. Further, using Arabidopsis plants altered in defense responses such as the transgenic lines NahG [defective in salicylic acid (SA) accumulation], and 35S-LOX2()) (defective in jasmonic acid production and hyper-accumulator of SA), and mutants ics1 (depleted in SA accumulation), and npr1-1 (non-expressor of pathogenesis-related protein) we show that resistance of Arabidopsis to typical plant pathogens and the animal pathogen S. aureus is conserved and is mediated by SA. The data presented here suggest that Arabidopsis thaliana resistance to S. aureus is mediated either by a direct effect of SA on the pathogen, specifically one that affects the attachment/aggregate formation on the root surface and reduces the pathogen's virulence, or by SA-dependent, NPR1-independent host responses.

Some pathogenic bacteria belong to a large, diverse group of species capable of infecting plants, animals, and humans. Enterococcus faecalis is an opportunistic human pathogen capable of infecting patients with a deficient immune system. Here we report that three E. faecalis strains (FA-2-2, V583, and OG1RF) are capable of infecting the leaves and roots of the model plant species Arabidopsis thaliana, causing plant mortality 7 days postinoculation. We found that E. faecalis pathogenesis in A. thaliana leaves is determined by the following series of events: attachment to leaf surface, entry through stomata or wounds, and colonization in intercellular spaces, leading to rotting and to the disruption of plant cell wall and membrane structures. The three E. faecalis strains colonize the roots of A. thaliana by forming a mosaic of large clusters of live bacteria on the root surface, as observed by scanning electron microscopy, phase-contrast microscopy, and fluorescence microscopy. To dissect the involvement of mammalian virulence-related factors in plant pathogenicity, we tested E. faecalis mutant strains ⌬fsrA (TX5240), ⌬fsrB (TX5266), ⌬fsrC (TX5242), ⌬gelE (TX5264), and ⌬sprE (TX5243), which correspond to virulence factors involved in pathogenesis in different animal models. Two E. faecalis virulencerelated factors that play an important role in mammalian and nematode models of infection, a putative quorum-sensing system (⌬fsrB) and serine protease (⌬sprE), were also found to be important for plant pathogenesis. The development of an E. faecalis-A. thaliana model system could potentially be used to circumvent certain inherent limitations that an animal model imposes on the identification and study of virulence factors. Furthermore, our study suggests an evolutionary crossover of virulence factors in plant, animal, and nematode pathogenesis.Enterococcus faecalis is a ubiquitous gram-positive bacterium that is usually found in soil and water (19,25). E. faecalis causes infections in such varied systems as the gastrointestinal tract, the skin and skin structures, the urinary tract, the bloodstream, and the heart (18, 23, 28), thus making it an important pathogen in hospital settings (9,19,23,24,26,39).E. faecalis presents a significant therapeutic challenge, due to its resistance to a vast array of antimicrobial drugs (cell wall-active agents, all commercially available aminoglycosides, penicillin, ampicillin, and vancomycin). The propensity of E. faecalis to acquire resistance may relate to its ability to participate in various forms of conjugation, which can result in the spread of genes as part of conjugative transposons, pheromone-responsive plasmids, or broad-host-range plasmids. The combination of these attributes suggests that this bacterium and its resistance to antimicrobial drugs will continue to pose a challenge (27,28,39). Several virulence-related factors have been described for E. faecalis, including cytolysin, a factor called aggregation substance, a zinc metalloprotease (gelatinase), and Fsr (an E. fa...