Abstract
Understanding the effects of spaceflight on plant flowering regulation is important to setup a life support system for long-term human space exploration. However, the way in which plant flowering is affected by spaceflight remains unclear. Here, we present results from our latest space experiments on the Chinese spacelab Tiangong-2, in which Arabidopsis wild-type and transgenic plants pFT::GFP germinated and grew as normally as their controls on the ground, but the floral initiation under the long-day condition in space was about 20 days later than their controls on the ground. Time-course series of digital images of pFT::GFP plants showed that the expression rhythm of FT in space did not change, but the peak appeared later in comparison with those of their controls on the ground. Whole-genome microarray analysis revealed that approximately 16% of Arabidopsis genes at the flowering stage changed their transcript levels under spaceflight conditions in comparison with their controls on the ground. The GO terms were enriched in DEGs with up-regulation of the response to temperature, wounding, and protein stabilization and down-regulation of the function in circadian rhythm, gibberellins, and mRNA processes. FT and SOC1 could act as hubs to integrate spaceflight stress signals into the photoperiodic flowering pathway in Arabidopsis in space.
Highlights
Long-duration manned space exploration will require close biological life support systems (BLSS) in which humans can live while reducing the minimum amount of water, oxygen, and nutrients to be transported and optimizing the recycling of reusable waste [1,2]
Arabidopsis wild-type (WT), pFT::green fluorescent protein (GFP) transgenic plants, and ft-10 mutant plants were grown in culture chambers (CCs), which were installed in plant culture boxes (PCBs) under microgravity (μ× g) on board the Chinese spacelab TG-2 (μ× g-PCB) and under normal gravity (1× g) on the ground either in PCB (1× g-PCB) or in a greenhouse (GH) (1× g-GH), as described above (Figure 1)
Image analyses suggested that FLOWERING LOCUS T (FT) expression in the leaves of plants under spaceflight conditions was apparently changed in comparison with that in the ground controls
Summary
Long-duration manned space exploration will require close biological life support systems (BLSS) in which humans can live while reducing the minimum amount of water, oxygen, and nutrients to be transported and optimizing the recycling of reusable waste [1,2]. Such a system will require an edible plant to be successfully cultivated long term in the environmental conditions expected to be achieved during spaceflight and on arrival at nearby objects [3]. The attempts of several pioneering space experiments to grow plants through a complete life cycle were unsuccessful because plants frequently delayed development or died in the transition from the vegetative to reproductive stages [10,11,12,13]
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