Sequence Exchange between Homologous NB-LRR Genes Converts Virus Resistance into Nematode Resistance, and Vice Versa.

Plants have evolved a limited repertoire of NB-LRR disease resistance (R) genes to protect themselves against myriad pathogens. This limitation is thought to be counterbalanced by the rapid evolution of NB-LRR proteins, as only a few sequence changes have been shown to be sufficient to alter resistance specificities toward novel strains of a pathogen. However, little is known about the flexibility of NB-LRR R genes to switch resistance specificities between phylogenetically unrelated pathogens. To investigate this, we created domain swaps between the close homologs Gpa2 and Rx1, which confer resistance in potato (Solanum tuberosum) to the cyst nematode Globodera pallida and Potato virus X, respectively. The genetic fusion of the CC-NB-ARC of Gpa2 with the LRR of Rx1 (Gpa2CN/Rx1L) results in autoactivity, but lowering the protein levels restored its specific activation response, including extreme resistance to Potato virus X in potato shoots. The reciprocal chimera (Rx1CN/Gpa2L) shows a loss-of-function phenotype, but exchange of the first three LRRs of Gpa2 by the corresponding region of Rx1 was sufficient to regain a wild-type resistance response to G. pallida in the roots. These data demonstrate that exchanging the recognition moiety in the LRR is sufficient to convert extreme virus resistance in the leaves into mild nematode resistance in the roots, and vice versa. In addition, we show that the CC-NB-ARC can operate independently of the recognition specificities defined by the LRR domain, either aboveground or belowground. These data show the versatility of NB-LRR genes to generate resistance to unrelated pathogens with completely different lifestyles and routes of invasion.

Nucleocytoplasmic distribution is required for activation of resistance by the potato NB-LRR receptor Rx1 and is balanced by its functional domains.

The Rx1 protein, as many resistance proteins of the nucleotide binding-leucine-rich repeat (NB-LRR) class, is predicted to be cytoplasmic because it lacks discernable nuclear targeting signals. Here, we demonstrate that Rx1, which confers extreme resistance to Potato virus X, is located both in the nucleus and cytoplasm. Manipulating the nucleocytoplasmic distribution of Rx1 or its elicitor revealed that Rx1 is activated in the cytoplasm and cannot be activated in the nucleus. The coiled coil (CC) domain was found to be required for accumulation of Rx1 in the nucleus, whereas the LRR domain promoted the localization in the cytoplasm. Analyses of structural subdomains of the CC domain revealed no autonomous signals responsible for active nuclear import. Fluorescence recovery after photobleaching and nuclear fractionation indicated that the CC domain binds transiently to large complexes in the nucleus. Disruption of the Rx1 resistance function and protein conformation by mutating the ATP binding phosphate binding loop in the NB domain, or by silencing the cochaperone SGT1, impaired the accumulation of Rx1 protein in the nucleus, while Rx1 versions lacking the LRR domain were not affected in this respect. Our results support a model in which interdomain interactions and folding states determine the nucleocytoplasmic distribution of Rx1.

Small subunit ribosomal DNA-based phylogenetic analysis of foliar nematodes (Aphelenchoides spp.) and their quantitative detection in complex DNA backgrounds.

Foliar nematodes, plant-parasitic representatives of the genus Aphelenchoides, constitute a minority in a group dominated by fungivorous species. Distinction between (mostly harmless) fungal feeding Aphelenchoides species and high impact plant parasites such as A. besseyi, A. fragariae, A. ritzemabosi, and A. subtenuis is severely hampered by the scarcity of informative morphological characters, some of which are only observable in specific developmental stages. Poor description of a number of non-plant-parasitic Aphelenchoides species further complicates identification. Based on (nearly) full-length small subunit ribosomal DNA (SSU rDNA) sequences (≈1,700 bp), a phylogenetic tree was generated, and the four target species appeared as distinct, well-supported groups. Notably, this genus does not constitute a monophyletic group: A. besseyi and A. ritzemabosi cluster together and they are phylogenetically isolated from A. fragariae, A. subtenuis, and most other fungivorous species. A phylum-wide SSU rDNA framework was used to identify species-specific DNA motifs. For the molecular detection of four plant-parasitic Aphelenchoides species, polymerase chain reaction primers were developed with high, identical annealing temperatures (63°C). Within the molecular framework presented here, these primers can be used for the rapid screening of plant material and soil for the presence of one or multiple foliar nematode species.

Profiles of moral distress and associated outcomes among student veterans.

OBJECTIVE: Military veterans who interpret their own or others' actions as moral transgressions are theorized to experience moral distress. The purpose of this study was to explore patterns of moral distress and associated psychological, social, and religious or spiritual problems among student veterans. METHOD: Student veterans (N = 498) retrospectively reported experiences of moral distress associated with deployment-related events in which they felt (a) troubled by what they witnessed, (b) troubled by what they did, (c) troubled by what they failed to do, (d) betrayed by military leaders, or (e) betrayed by fellow service members. RESULTS: Latent profile analysis revealed 5 response patterns: No Moral Distress (42%), Witnessing-Only (16%), Moral Distress-Other (19%; encompassing distress mostly from being betrayed by others), Moral Distress-Self (8%; encompassing distress mostly from one's own actions or inactions), and Moral Distress-Self and Other (15%). We compared scores on measures of posttraumatic stress, familial or social functioning, and religious or spiritual struggles between profiles and observed moderate to large differences. CONCLUSIONS: Whereas participants reported some problems (e.g., interpersonal conflict) regardless of whether they were exposed to a morally injurious event by witnessing, perpetrating, or being betrayed, in comparison to those reporting no moral distress, those who felt responsible for the event reported greater guilt and lack of purpose and those who held others responsible for the event reported greater posttraumatic stress. Participants who endorsed feeling betrayed by others' and troubled by their own actions reported multiple problems including posttraumatic stress, interpersonal difficulties, and religious or spiritual struggles. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Functional analysis of cysteine residues of ECP elicitor proteins of the fungal tomato pathogen Cladosporium fulvum.

summary A striking feature of all elicitor proteins of Cladosporium fulvum that are specifically recognized by tomato is that they contain an even number of cysteine residues. These cysteine residues are thought to be involved in disulphide bridges. In this study, a mutational analysis of the cysteine residues of ECP1, ECP2 and ECP5 was performed, to examine their role in stability and hypersensitive response-inducing activity of the proteins. We show that not all cysteine residues of the ECPs are critical for the hypersensitive response-inducing activity of the proteins, and we propose that the role of cysteine residues in the ECPs is more complex than anticipated.