The transcriptome of Arabidopsis thaliana during systemic acquired resistance.

Infected plants undergo transcriptional reprogramming during initiation of both local defence and systemic acquired resistance (SAR). We monitored gene-expression changes in Arabidopsis thaliana under 14 different SAR-inducing or SAR-repressing conditions using a DNA microarray representing approximately 25-30% of all A. thaliana genes. We derived groups of genes with common regulation patterns, or regulons. The regulon containing PR-1, a reliable marker gene for SAR in A. thaliana, contains known PR genes and novel genes likely to function during SAR and disease resistance. We identified a common promoter element in genes of this regulon that binds members of a plant-specific transcription factor family. Our results extend expression profiling to definition of regulatory networks and gene discovery in plants.

LSD1 regulates salicylic acid induction of copper zinc superoxide dismutase in Arabidopsis thaliana.

We characterized the accumulation patterns of Arabidopsis thaliana proteins, two CuZnSODs, FeSOD, MnSOD, PR1, PR5, and GST1, in response to various pathogen-associated treatments. These treatments included inoculation with virulent and avirulent Pseudomonas syringae strains, spontaneous lesion formation in the lsd1 mutant, and treatment with the salicylic acid (SA) analogs INA (2,6-dichloroisonicotinic acid) and BTH (benzothiadiazole). The PR1, PR5, and GST1 proteins were inducible by all treatments tested, as expected from previous mRNA blot analysis. The two CuZnSOD proteins were induced by SA analogs and in conjunction with lsd1-mediated spreading cell death. Additionally, LSD1 is a part of a signaling pathway for the induction of the CuZnSOD proteins in response to SA but not in lsd1-mediated cell death. We suggest that the spreading lesion phenotype of lsd1 results from a lack of up-regulation of a CuZnSOD responsible for detoxification of accumulating superoxide before the reactive oxygen species can trigger a cell death cascade.

Induced plant defence responses: scientific and commercial development possibilities.

Recent work has demonstrated that plants have endogenous defence mechanisms that can be induced as a response to attack by insects and pathogens. There are two well-studied examples of these induced defence responses. Systemic acquired resistance (SAR) results in increased resistance to a broad spectrum of pathogens throughout a plant in response to localized necrosis caused by pathogen infection. The second example is the systemic induction of proteinase inhibitors to deter feeding by herbivores following an initial event of feeding. In addition, there is now preliminary evidence for other induced defence response pathways. By understanding the breadth of induced defence responses and the mechanisms used to control these pathways, novel plant protection strategies may be developed for use in agronomic settings. Rather than reducing crop losses caused by pests or pathogens by using chemicals that are designed to kill the offending organism, the plant's own defence mechanisms can be used to limit damage due to pests. Novel crop protection strategies based on genetic or chemical regulation of these induced responses show great potential. The first example of a crop protection product that acts by inducing an endogenous defence response pathway is now on the market. Bion reduces the level of pathogen infection in plants by activating SAR.

Salicylate-independent lesion formation in Arabidopsis lsd mutants.

In many interactions of plants with pathogens, the primary host defense reaction is accompanied by plant cell death at the site of infection. The resulting lesions are correlated with the establishment of an inducible resistance in plants called systemic acquired resistance (SAR), for which salicylic acid (SA) accumulation is a critical signaling event in Arabidopsis and tobacco. In Arabidopsis, the lesions simulating disease (lsd) mutants spontaneously develop lesions in the absence of pathogen infection. Furthermore, lsd mutants express SAR marker genes when lesions are present and are resistant to the same spectrum of pathogens as plants activated for SAR by necrogenic pathogen infection. To assess the epistatic relationship between SA accumulation and cell death, transgenic Arabidopsis unable to accumulate SA due to the expression of the salicylate hydroxylase (nahG) gene were used in crosses with the dominant mutants lsd2 or lsd4. Progeny from the crosses were inhibited for SAR gene expression and disease resistance. However, these progeny retained the spontaneous cell death phenotype similar to siblings not expressing nahG. Because lesions form in the absence of SA accumulation for isd2 and lsd4, a model is suggested in which lesion formation in these two mutants is determined prior to SA accumulation in SAR signal transduction. By contrast, the loss of SAR gene expression and disease resistance in nahG-expressing lsd mutants indicates that these traits are dependent upon SA accumulation in the SAR signal transduction pathway.

A novel zinc finger protein is encoded by the Arabidopsis LSD1 gene and functions as a negative regulator of plant cell death.

Arabidopsis Isd1 mutants are hyperresponsive to cell death initiators and fail to limit the extent of cell death. Superoxide is a necessary and sufficient signal for cell death propagation. Thus, LSD1 monitors a superoxide-dependent signal and negatively regulates a plant cell death pathway. We isolated LSD1 via its map position. The predicted LSD1 protein contains three zinc finger domains, defined by CxxCxRxxLMYxxGASxVxCxxC. These domains are present in three additional Arabidopsis genes, suggesting that LSD1 defines a zinc finger protein subclass. LSD1 is constitutively expressed, consistent with the mutant phenotype. Alternate splicing gives rise to a low abundance mRNA encoding an extra five amino-terminal amino acids. We propose that LSD1 regulates transcription, via either repression of a prodeath pathway or activation of an antideath pathway, in response to signals emanating from cells undergoing pathogen-induced hypersensitive cell death.

Initiation of runaway cell death in an Arabidopsis mutant by extracellular superoxide.

Reactive oxygen intermediates (ROIs) regulate apoptosis during normal development and disease in animals. ROIs are also implicated in hypersensitive resistance responses of plants against pathogens. Arabidopsis lsd1 mutants exhibited impaired control of cell death in the absence of pathogen and could not control the spread of cell death once it was initiated. Superoxide was necessary and sufficient to initiate lesion formation; it accumulated before the onset of cell death and subsequently in live cells adjacent to spreading lsd1 lesions. Thus, runaway cell death seen in lsd1 plants reflected abnormal accumulation of superoxide and lack of responsiveness to signals derived from it.

Perception and response in plant disease resistance.

Plants express sophisticated mechanisms for recognizing pathogens. The functionally defined repertoire of non-self perception is large; the number and nature of subsequent molecular events required for resistance is unknown. Recent cloning of disease resistance genes, and genetic identification of loci required for their function, allows dissection of the structure, evolution, and deployment within populations of pathogen-perception mechanisms. Roles for reactive oxygen species and programmed cell death in resistance have also been suggested recently. New results document a role for salicylic acid as a lynchpin in the establishment and maintenance of the 'effector functions' of disease resistance, and strategies for engineered plant protection are moving closer to reality.

Arabidopsis mutants simulating disease resistance response.

We describe six Arabidopsis mutants, defining at least four loci, that spontaneously form necrotic lesions on leaves. Lesions resemble those resulting from disease, but occur in the absence of pathogen. In five mutants, lesion formation correlates with expression of histochemical and molecular markers of plant disease resistance responses and with expression of genes activated during development of broad disease resistance in plants (systemic acquired resistance [SAR]). We designate this novel mutant class Isd (for lesions simulating disease resistance response). Strikingly, four Isd mutants express substantial resistance to virulent fungal pathogen isolates. Isd mutants vary in cell type preferences for lesion onset and spread. Lesion formation can be conditional and can be induced specifically by biotic and chemical activators of SAR in Isd1 mutants.

Downstream DNA sequences are required to activate a gene expressed in the root cortex of embryos and seedlings.

We showed previously that a gene, designated AX92, which is expressed at an early stage of cortex differentiation in the root apex of oilseed rape seedlings, is also expressed in embryos. To compare AX92 gene regulation during embryo-genesis and postembryonic growth, we constructed a chimeric gene consisting of AX92 5' and 3' untranslated and flanking regions fused with a beta-glucuronidase protein coding region. We showed that the chimeric gene is active in both developing cortex cells in the root apical meristems of transgenic oilseed rape seedlings and in cortex cells at the root end of embryonic axes. To determine whether the AX92 gene is regulated by a common mechanism in embryos and seedlings, we analyzed the expression of modified chimeric genes. We showed that the AX92 chimeric gene is regulated combinatorially and that DNA sequences located 3' of the protein coding region are necessary for its activation in the root cortex of both embryos and seedlings. Our results suggest that common regulatory sequences are required to activate the gene in the embryonic and postembryonic root cortex.

Rhodotorula rubra contamination in fiberoptic bronchoscopy.

Rhodotorula rubra was recovered in 18 bronchoscopic specimens from 15 patients from May to November 1987. One hundred and twenty-one bronchoscopies were performed during that period by two bronchoscopists (W. W.; R.D.) at Letterman Army Medical Center in San Francisco. Isolation of R rubra occurred in 11 bronchoalveolar lavage (BAL) specimens, four bronchial washes, and three transbronchial biopsies. Clinical infection was not present in any of these patients, although five were immunocompromised hosts. After a stepwise infection control review of the laboratory, the bronchoscopy suite, bronchoscopists, and the fiberoptic bronchoscope failed to recover the organism, a systematic evaluation of the cleaning procedure was undertaken. We discovered that replacement of the suction valve and the rubber biopsy valve on the biopsy channel immediately after cleaning allowed moisture to accumulate in these areas. Removal of both the suction valve and biopsy valve during periods of nonuse resulted in adequate drying of the biopsy channel and eradication of contamination from December 1987 to May 1990 (350 bronchoscopies). Epidemiologic and infection control surveillance is critical for bronchoscopy, especially when possible pathogens are recovered by BAL in the immunocompromised patient.

Expression of a Brassica napus Malate Synthase Gene in Transgenic Tomato Plants during the Transition from Late Embryogeny to Germination.

To study gene regulation during the transition from late embryogeny to germination, we have analyzed the expression of a gene encoding the glyoxylate cycle enzyme malate synthase in transgenic tomato (Lycopersicon esculentum) plants. We have shown that although there are at least four classes of malate synthase genes in Brassica napus L., one gene is expressed at a high level during both late embryogeny and postgermination. Analyses of transgenic tomato plants containing the expressed B. napus gene along with 4.7 and 1.0 kilobase pairs of 5' and 3' flanking sequences, respectively, confirmed that a single gene is expressed at both stages of development. Furthermore, localization studies have shown that mRNA encoded by the B. napus gene is distributed throughout the tissues of a mature embryo but is not detected in the vascular cylinder of a seedling. We conclude that the sequences required to qualitatively regulate the gene correctly over the plant life cycle are present within the transferred gene and/or flanking regions. Moreover, the malate synthase gene is regulated differently during late embryogeny and postgermination in the developing vascular cylinder.

Relationship of strain 19 calfhood vaccination in beef herds and brucellosis reactor rates, duration of quarantine, and number of herd tests.

Initial and cumulative reactor rates for strain 19 vaccinates and nonvaccinates were significantly (P less than 0.001) lower for beef herds containing variable proportions of vaccinates, compared with reactor rates in nonvaccinated herds. In addition, significant (P less than 0.005) reduction in cumulative incidence was observed in nonvaccinated and strain 19-vaccinated cattle as the proportion of vaccinates within the herd increased from 1 to 19%, 20 to 39%, 40 to 59%, and 60 to 100%. Duration of quarantine and number of herd tests were not reduced in herds with strain 19-vaccinated cattle. In herds released from quarantine, duration of quarantine and number of tests were positively correlated to proportion of the herd vaccinated. In nonvaccinated herds released from quarantine, effect of herd size was documented by strong positive (P = 0.042) correlation with duration of quarantine and slightly weaker correlation (P = 0.095) with number of tests.

Sarcoidosis complicated by HIV infection: three case reports and a review of the literature.

We report three cases of sarcoidosis complicated by human immunodeficiency virus (HIV) infection and review four other isolated case reports in the literature. There is clinical overlap of both diseases, including symptoms, pulmonary function abnormalities, and lymphocyte function. Bronchoalveolar lavage (BAL) in these patients showed a lymphocytic alveolitis without pathogens. BAL lymphocyte subset analysis showed markedly depressed CD4+/CD8+ ratios in three patients. These data were clinically useful for distinguishing the CD8+ alveolitis associated with HIV infection from the CD4+ alveolitis associated with sarcoidosis. Three patients improved with corticosteroid therapy. Two patients with BAL-documented CD8+ alveolitis tolerated discontinuation of steroids. One patient's sarcoidosis improved without therapy concurrent with the diagnosis of Kaposi's sarcoma. Another patient developed sarcoidosis 1 yr after manifesting HIV positive serology. BAL can be used to distinguish the lymphocytic alveolitis of sarcoidosis from that associated with HIV infection. Patients with active sarcoidosis complicated by HIV infection can be effectively treated with corticosteroid therapy.

Pulmonary hyperinfection syndrome with Strongyloides stercoralis.

A 65-year-old man with steroid-dependent chronic airflow obstruction presented with progressive dyspnea and weight loss. Travel history included a military tour in southeast Asia. A chest roentgenogram revealed hyperexpanded lung fields with diffusely increased interstitial markings. The Papanicolaou stain of expectorated sputum demonstrated the rhabditiform larvae of Strongyloides stercoralis. Endemic areas of infection include the southeastern United States, Puerto Rico, Central America, the Pacific basin, and central Africa. In recent immigrant groups and veterans of the Vietnam conflict, rates of infection are as high as 6 percent. The hyperinfection syndrome occurs in immunocompromised hosts and is associated with glucocorticoid steroid therapy. This allows massive proliferation of larval forms. Clinical clues include an appropriate travel history (even in the remote past), gastrointestinal symptoms, cutaneous symptoms, eosinophilia, or thrombocytosis. Our patient demonstrated a classic presentation of the hyperinfection syndrome, and the condition responded well to thiabendazole.

Sleep apnea syndrome after irradiation of the neck.

After irradiation of the neck for a squamous cell carcinoma of the tonsillar pillar and vocal cord, a 71-year-old man presented with a rapidly progressive sleep apnea syndrome. Previous reports describe the condition of patients with obstructive sleep apnea that developed after neck irradiation and secondary to supraglottic edema. Our patient had an obstructive component to his apnea similar to that described in previous cases, but, in addition, he had hypothyroidism. Myxedema is a well-described cause of both obstructive and central apnea. We believe both contributed to his condition. He was successfully treated by placement of a tracheostomy and by thyroid supplementation. In patients who present with sleep apnea after neck irradiation, especially with acute or severe symptoms, the differential diagnosis should include both a central cause from hypothyroidism as well as a peripheral obstructive cause from laryngeal edema.