Transgene Expression Patterns Indicate That Spaceflight Affects Stress Signal Perception and Transduction in Arabidopsis

Abstract

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 ␤-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.

Hypobaric Biology: Arabidopsis Gene Expression at Low Atmospheric Pressure

“…Adh, although not represented in the Affymetrix array used in these analyses, is a well-characterized hypoxia-induced gene (e.g. Paul et al, 2001;Klok et al, 2002). Adh was induced by hypobaria and hypoxia to similar levels.…”

“…The culture conditions preceding the LPGC environmental treatments consisted of 9 d of growth in continuous light (70-80 mol m Ϫ2 s Ϫ1 ) at 22°C to 24°C. These growth conditions produce no overt or incipient hypoxia due to roots penetrating the agar substrate (Paul et al, 2001). The experimental treatments were conducted on two separate occasions.…”

“…A, A prototype LPGC was designed to control total pressure, gas composition, temperature, and light. B, The plants were grown on vertically oriented agar plates and, as such, had ample water supply, and the entire mass of roots and shoots was exposed to the atmospheric environment (Paul et al, 2001), before harvesting the shoots for RNA isolation and array analyses. For hypobaria, the total pressure was held at 10 kPa of Earth-normal air, whereas for hypoxia, the pressure was held at 101 kPa with flow of 98% N 2 :2% O 2 (v/v).…”

“…Arabidopsis (ecotype Wassilewskija [WS]) plants were grown on nutrient media agar plates held in the vertical position to encourage root growth along the aerated and exposed surface of the agar (Paul et al, 2001; Fig. 1B).…”

Flexible imaging payload for real-time fluorescent biological imaging in parabolic, suborbital and space analog environments

“…Localized hypoxia was created by covering a section of the roots growing along the surface of the base layer of phytagel with an additional layer of solidified gel. This blanket over the roots slowly reduces the amount of available oxygen in the region, which induces the transcription of the Adh gene and any reporter gene constructed with the Adh promoter region (Paul et al, 2001). …”