Plants utilize variation in day length (photoperiod) to anticipate seasonal changes. They respond by modulating their growth and development to maximize seed production, which in cereal crops is directly related to yield. In wheat (Triticum aestivum), the acceleration of flowering under long days (LD) is dependent on the light induction of PHOTOPERIOD1 (PPD1) by phytochromes. Under LD, PPD1 activates FLOWERING LOCUS T1 (FT1), a mobile signaling protein that travels from the leaves to the shoot apical meristem to promote flowering. Here, we show that the interruption of long nights by short pulses of light ("night-break" [NB]) accelerates wheat flowering, suggesting that the duration of the night is critical for wheat photoperiodic response. PPD1 transcription was rapidly upregulated by NBs, and the magnitude of this induction increased with the length of darkness preceding the NB. Cycloheximide abolished the NB up-regulation of PPD1, suggesting that this process is dependent on active protein synthesis during darkness. While one NB was sufficient to induce PPD1, more than 15 NBs were required to induce high levels of FT1 expression and a strong acceleration of flowering. Multiple NBs did not affect the expression of core circadian clock genes. The acceleration of flowering by NB disappeared in ppd1-null mutants, demonstrating that this response is mediated by PPD1. The acceleration of flowering was strongest when NBs were applied in the middle of the night, suggesting that in addition to PPD1, other circadiancontrolled factors are required for the up-regulation of FT1 expression and the acceleration of flowering.Plants can anticipate diurnal and seasonal fluctuations in their environment and adjust their growth and development to coincide with favorable conditions. In flowering plants, reproductive development must be optimally timed to minimize the risk of damage to sensitive floral organs by late frosts or early high temperatures. The correct timing of this transition is a major determinant of reproductive success and, in cereal crops such as wheat (Triticum aestivum), of grain yield. Therefore, an improved understanding of the regulation of flowering time can contribute to the development of crop varieties better adapted to diverse environments. Photoperiodic flowering responses vary in different species; short-day (SD) plants and long-day (LD) plants exhibit accelerated flowering in SD and LD, respectively, while day-neutral plants exhibit similar flowering profiles irrespective of day length Allard, 1920, 1923). Plants possess complex regulatory mechanisms to perceive and respond to changes in photoperiod, which ensure that flowering occurs only under inductive conditions. The regulation of flowering time by photoperiod is best understood in Arabidopsis (Arabidopsis thaliana), a LD plant where the photoperiodic response is mainly controlled by CONSTANS (CO). CO expression is regulated by the circadian clock and peaks in the late afternoon and evening (Suárez-López et al., 2001). The CO protein is destabili...

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BackgroundVery little is known about the immunological responses of amphibians to pathogens that are causing global population declines. We used a custom microarray gene chip to characterize gene expression responses of axolotls (Ambystoma mexicanum) to an emerging viral pathogen, Ambystoma tigrinum virus (ATV).ResultAt 0, 24, 72, and 144 hours post-infection, spleen and lung samples were removed for estimation of host mRNA abundance and viral load. A total of 158 up-regulated and 105 down-regulated genes were identified across all time points using statistical and fold level criteria. The presumptive functions of these genes suggest a robust innate immune and antiviral gene expression response is initiated by A. mexicanum as early as 24 hours after ATV infection. At 24 hours, we observed transcript abundance changes for genes that are associated with phagocytosis and cytokine signaling, complement, and other general immune and defense responses. By 144 hours, we observed gene expression changes indicating host-mediated cell death, inflammation, and cytotoxicity.ConclusionAlthough A. mexicanum appears to mount a robust innate immune response, we did not observe gene expression changes indicative of lymphocyte proliferation in the spleen, which is associated with clearance of Frog 3 iridovirus in adult Xenopus. We speculate that ATV may be especially lethal to A. mexicanum and related tiger salamanders because they lack proliferative lymphocyte responses that are needed to clear highly virulent iridoviruses. Genes identified from this study provide important new resources to investigate ATV disease pathology and host-pathogen dynamics in natural populations.

Alternative routes of administration are one approach that could be used to bypass the blood–brain barrier (BBB) for effective drug delivery to the central nervous system (CNS). Here, we focused on intranasal delivery of polymer nanoparticles. We hypothesized that surface modification of poly(lactic-co-glycolic acid) (PLGA) nanoparticles with rabies virus glycoprotein (RVG29) would increase residence time and exposure of encapsulated payload to the CNS compared to non-targeted nanoparticles. Delivery kinetics and biodistribution were analyzed by administering nanoparticles loaded with the carbocyanine dye 1,1′-Dioctadecyl-3,3,3′,3′-Tetramethylindotricarbocyanine Iodide (DiR) to healthy mice. Intranasal administration yielded minimal exposure of nanoparticle payload to most peripheral organs and rapid, effective delivery to whole brain. Regional analysis of payload delivery within the CNS revealed higher delivery to tissues closest to the trigeminal nerve, including the olfactory bulb, striatum, midbrain, brainstem, and cervical spinal cord. RVG29 surface modifications presented modest targeting benefits to the striatum, midbrain, and brainstem 2 h after administration, although targeting was not observed 30 min or 6 h after administration. Payload delivery to the trigeminal nerve was 3.5× higher for targeted nanoparticles compared to control nanoparticles 2 h after nanoparticle administration. These data support a nose-to-brain mechanism of drug delivery that closely implicates the trigeminal nerve for payload delivery from nanoparticles via transport of intact nanoparticles and eventual diffusion of payload. Olfactory and CSF routes are also observed to play a role. These data advance the utility of targeted nanoparticles for nose-to-brain drug delivery of lipophilic payloads and provide mechanistic insight to engineer effective delivery vectors to treat disease in the CNS.