Spaceflight Transcriptomes: Unique Responses to a Novel Environment

Abstract

The spaceflight environment presents unique challenges to terrestrial biology, including but not limited to the direct effects of gravity. As we near the end of the Space Shuttle era, there remain fundamental questions about the response and adaptation of plants to orbital spaceflight conditions. We address a key baseline question of whether gene expression changes are induced by the orbital environment, and then we ask whether undifferentiated cells, cells presumably lacking the typical gravity response mechanisms, perceive spaceflight. Arabidopsis seedlings and undifferentiated cultured Arabidopsis cells were launched in April, 2010, as part of the BRIC-16 flight experiment on STS-131. Biologically replicated DNA microarray and averaged RNA digital transcript profiling revealed several hundred genes in seedlings and cell cultures that were significantly affected by launch and spaceflight. The response was moderate in seedlings; only a few genes were induced by more than 7-fold, and the overall intrinsic expression level for most differentially expressed genes was low. In contrast, cell cultures displayed a more dramatic response, with dozens of genes showing this level of differential expression, a list comprised primarily of heat shock-related and stress-related genes. This baseline transcriptome profiling of seedlings and cultured cells confirms the fundamental hypothesis that survival of the spaceflight environment requires adaptive changes that are both governed and displayed by alterations in gene expression. The comparison of intact plants with cultures of undifferentiated cells confirms a second hypothesis: undifferentiated cells can detect spaceflight in the absence of specialized tissue or organized developmental structures known to detect gravity.

Seed-to-Seed-to-Seed Growth and Development of Arabidopsis in Microgravity

“…The majority of these plants, which underwent germination stress and delayed sprouting, were then harvested for gene expression analysis at approximately 4 weeks of age. It is therefore difficult to compare the results of our study with the recently conducted well-controlled transcriptional analysis of 12-day-old Arabidopsis plants grown on phytagel plates within the Advanced Biological Research System on a space shuttle (Paul et al, 2012(Paul et al, , 2013b.…”

Mechanisms of disruption of meristematic competence by microgravity inArabidopsisseedlings

“…Actually, in both plant and animal cells it has been reported the perception of mechanical signals by cells not apparently specialized in gravity sensing [20][21][22] and, in several laboratories, different research groups, including us, have reported genomic and proteomic effects of an altered gravity environment (even of spaceflight) on Arabidopsis callus cell cultures. [23][24][25][26][27] In the case of the magnetic levitation, the response at the meristematic cell level is associated to an altered polar auxin transport; this means that there should be an intermediate factor capable of linking the signal sensed in the cell by the diamagnetic levitation of water and the alteration of the polar auxin transport. In turn, cell cultures lack both, gravitropic signals induced by statolith movements and polar auxin transport However, gravity alteration is sensed by cells and results in cellular and molecular effects, also including disruption of meristematic competence (unpublished results).…”

Space, the final frontier: A critical review of recent experiments performed in microgravity

“…Additionally, the potential non-microgravity spaceflight effects in the BRIC-PDF system are increased by the lack of ability to initiate germination in flight (seeds germinate on the ground prior to launch), exposing the germinating seedlings to the stresses of vehicle launch. The BRIC-PDF system was utilized with subsequent RT-qPCR and microarray experiments to analyze differences in transcription between cell cultures and whole plants flown in microgravity conditions for 12 days [16]. There was a much more dramatic transcription response in cell cultures when compared to ground control, however the lack of a 1-g in-flight control limits the ability to determine if the cell culture response in due to microgravity or other spaceflight influences or due to the stresses of launch.…”