Cross-protection triggered by a mild strain of virus acts as a prophylaxis to prevent subsequent infections by related viruses in plants; however, the underling mechanisms are not fully understood. Through mutagenesis, we isolated a mutant strain of Turnip mosaic virus (TuMV), named Tu-GK, that contains an Arg182Lys substitution in helper component-proteinase (HC-Pro(K)) that confers complete cross-protection against infection by a severe strain of TuMV in Nicotiana benthamiana, Arabidopsis thaliana Col-0, and the Arabidopsis dcl2-4/dcl4-1 double mutant defective in DICER-like ribonuclease (DCL)2/DCL4-mediated silencing. Our analyses showed that HC-Pro(K) loses the ability to interfere with microRNA pathways, although it retains a partial capability for RNA silencing suppression triggered by DCL. We further showed that Tu-GK infection triggers strong salicylic acid (SA)-dependent and SA-independent innate immunity responses. Our data suggest that DCL2/4-dependent and -independent RNA silencing pathways are involved, and may crosstalk with basal innate immunity pathways, in host defense and in cross-protection.
Plant microRNAs (miRNA) guide cleavage of target mRNAs by DICER-like proteins, thereby reducing mRNA abundance. Native precursor miRNAs can be redesigned to target RNAs of interest, and one application of such artificial microRNA (amiRNA) technology is to generate plants resistant to pathogenic viruses. Transgenic Arabidopsis plants expressing amiRNAs designed to target the genome of two unrelated viruses were resistant, in a highly specific manner, to the appropriate virus. Here, we pursued two different goals. First, we confirmed that the 21-nt target site of viral RNAs is both necessary and sufficient for resistance. Second, we studied the evolutionary stability of amiRNA-mediated resistance against a genetically plastic RNA virus, TuMV. To dissociate selective pressures acting upon protein function from those acting at the RNA level, we constructed a chimeric TuMV harboring a 21-nt, amiRNA target site in a non-essential region. In the first set of experiments designed to assess the likelihood of resistance breakdown, we explored the effect of single nucleotide mutation within the target 21-nt on the ability of mutant viruses to successfully infect amiRNA-expressing plants. We found non-equivalency of the target nucleotides, which can be divided into three categories depending on their impact in virus pathogenicity. In the second set of experiments, we investigated the evolution of the virus mutants in amiRNA-expressing plants. The most common outcome was the deletion of the target. However, when the 21-nt target was retained, viruses accumulated additional substitutions on it, further reducing the binding/cleavage ability of the amiRNA. The pattern of substitutions within the viral target was largely dominated by G to A and C to U transitions.
This study examined the unique and combined associations of homelessness and school mobility with educational well-being indicators, as well as the mediating effect of absenteeism, for an entire cohort of third-grade students in Philadelphia. Using integrated archival administrative data from the public school district and the municipal Office of Supportive Housing, multilevel linear models were estimated to test these associations while adjusting for nesting of students within schools. Findings demonstrated that homelessness had a unique association with problems in classroom engagement, school mobility was uniquely related to both academic achievement and problems in classroom engagement, and experiencing both homelessness and school mobility was the most detrimental for both forms of educational well-being. Absenteeism was found to partially mediate the relations between homelessness, school mobility, and problems in task engagement. Results provide support for the McKinney-Vento Homeless Assistance Act and the need for educational policies for mobile children.
School mobility has been shown to increase the risk of poor achievement, behavior problems, grade retention, and high school drop-out. Using data over 25 years from the Chicago Longitudinal Study, we investigated the unique risk of school moves on a variety of young adult outcomes including educational attainment, occupational prestige, depression symptoms, and criminal arrests. We also investigated how the timing of school mobility, whether earlier or later in the academic career, may differentially predict these outcomes over and above associated risks. Results indicate that students who experience more school changes between kindergarten and twelfth grade are less likely to complete high school on time, complete fewer years of school, attain lower levels of occupational prestige, are more likely to experience symptoms of depression, and are more likely to be arrested as adults. Furthermore, the number of school moves predicted above and beyond associated risks such as residential mobility and family poverty. When timing of school mobility was examined, results indicated more negative outcomes associated with moves later in the grade school career, particularly between fourth and eighth grade.
This describes the scouting report as an approach that social and behavior intervention specialists can use to help middle-level teachers create social contexts that support productive social roles and relationships of students with disabilities. Building from research on early adolescent social dynamics and context-based interventions to support students' adjustment in middle-level classrooms, this manuscript describes the scouting report approach as an information collection process that can be used to (a) guide the selection and tailoring of evidence-based interventions to address the social difficulties and support needs of students with disabilities and (b) manage general social dynamics in ways that promote a positive peer culture across the classroom. A step-by-step description of the scouting report process is presented along with sample scenarios to help guide intervention specialists as they provide consultation support to middle-level general education teachers who serve students with disabilities in their classes.
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