Transgene expression patterns indicate that spaceflight affects stress signal perception and transduction in arabidopsis.

The use of plants as integral components of life support systems remains a cornerstone of strategies for long-term human habitation of space and extraterrestrial colonization. Spaceflight experiments over the past few decades have refined the hardware required to grow plants in low-earth orbit and have illuminated fundamental issues regarding spaceflight effects on plant growth and development. Potential incipient hypoxia, resulting from the lack of convection-driven gas movement, has emerged as a possible major impact of microgravity. We developed transgenic Arabidopsis containing the alcohol dehydrogenase (Adh) gene promoter linked to the beta-glucuronidase (GUS) reporter gene to address specifically the possibility that spaceflight induces the plant hypoxia response and to assess whether any spaceflight response was similar to control terrestrial hypoxia-induced gene expression patterns. The staining patterns resulting from a 5-d mission on the orbiter Columbia during mission STS-93 indicate that the Adh/GUS reporter gene was activated in roots during the flight. However, the patterns of expression were not identical to terrestrial control inductions. Moreover, although terrestrial hypoxia induces Adh/GUS expression in the shoot apex, no apex staining was observed in the spaceflight plants. This indicates that either the normal hypoxia response signaling is impaired in spaceflight or that spaceflight inappropriately induces Adh/GUS activity for reasons other than hypoxia.

Spaceflight exposure effects on transcription, activity, and localization of alcohol dehydrogenase in the roots of Arabidopsis thaliana.

Although considerable research and speculation have been directed toward understanding a plant's perception of gravity and the resulting gravitropic responses, little is known about the role of gravity-dependent physical processes in normal physiological function. These studies were conducted to determine whether the roots of plants exposed to spaceflight conditions may be experiencing hypoxia. Arabidopsis thaliana (L.) Heynh. plants were grown in agar medium during 6 or 11 d of spaceflight exposure on shuttle missions STS-54 (CHROMEX-03) and STS-68 (CHROMEX-05), respectively. The analysis included measurement of agar redox potential and root alcohol dehydrogenase (ADH) activity, localization, and expression. ADH activity increased by 89% as a result of spaceflight exposure for both CHROMEX-03 and -05 experiments, and ADH RNase protection assays revealed a 136% increase in ADH mRNA. The increase in ADH activity associated with the spaceflight roots was realized by a 28% decrease in oxygen availability in a ground-based study; however, no reduction in redox potential was observed in measurements of the spaceflight bulk agar. Spaceflight exposure appears to effect a hypoxic response in the roots of agar-grown plants that may be caused by changes in gravity-mediated fluid and/or gas behavior.

Pleiotropic defects in ataxia-telangiectasia protein-deficient mice.

We have generated a mouse model for ataxia-telangiectasia by using gene targeting to generate mice that do not express the Atm protein. Atm-deficient mice are retarded in growth, do not produce mature sperm, and exhibit severe defects in T cell maturation while going on to develop thymomas. Atm-deficient fibroblasts grow poorly in culture and display a high level of double-stranded chromosome breaks. Atm-deficient thymocytes undergo spontaneous apoptosis in vitro significantly more than controls. Atm-deficient mice then exhibit many of the same symptoms found in ataxia-telangiectasia patients and in cells derived from them. Furthermore, we demonstrate that the Atm protein exists as two discrete molecular species, and that loss of one or of both of these can lead to the development of the disease.

Molecular organization and tissue-specific expression of an Arabidopsis 14-3-3 gene.

The 14-3-3 proteins, originally described as mammalian brain proteins, are ubiquitous in eukaryotes. We isolated an Arabidopsis 14-3-3 gene, designated GRF1-GF14 chi (for general regulatory factor1-G-box factor 14-3-3 homolog isoform chi), and characterized its expression within plant tissues. Sequence comparison of the GRF1-GF14 chi genomic clone with other 14-3-3 proteins demonstrated that the extreme conservation of 14-3-3 residues in several domains is encoded by the first three exons. The highly variable C-terminal domain is encoded by a divergent fourth exon that is unique among 14-3-3 homologs, suggesting that exon shuffling might confer gene-specific functions among the isoforms. The anatomical distribution and developmental expression of the Arabidopsis 14-3-3 protein were examined in transgenic plants carrying a GRF1-GF14 chi promoter-beta-glucuronidase construct. GF14 chi promoter activity was observed in the roots of both seedlings and mature plants. In immature flowers, GF14 chi promoter activity was localized to the buds. However, as the flowers matured, GF14 chi promoter activity was restricted to the stigma, anthers, and pollen. In immature siliques, GF14 chi promoter activity was initially localized to styles and abscission zones but was subsequently observed throughout mature siliques. In situ hybridization demonstrated that GF14 chi mRNA expression was prominent in epidermal tissue of roots, petals, and sepals of flower buds, papillae cells of flowers, siliques, and endosperm of immature seeds. Thus, plant 14-3-3 gene expression exhibits cell- and tissue-specific localization rivaling that observed for 14-3-3 proteins within the mammalian brain.