Plants are vital to human space exploration, providing oxygen, food, and psychological benefits to astronauts while contributing to water regeneration through recycling of organic wastes. However, microgravity or reduced gravity in space presents a significant environmental challenge to plant growth. Understanding plant biology in both gravity and microgravity conditions is therefore critical for advancing space exploration. In recent years, substantial progress has been made in understanding how gravity affects plants and its implications for the future of space agriculture, although a more comprehensive review is still needed. This review offers an overview of technological platforms to simulate and study effects of microgravity, detailing their historical background and key characteristics. It also summarizes recent advances in understanding plant gravitropism, including critical steps, such as gravity sensing, signal transduction, and curvature response. The impacts of microgravity on plants are examined at the phenotypic, cellular, and molecular levels. Studies on plant biology in microgravity have significantly expanded our knowledge, laying the foundation for the future of space agriculture and exploration. Additionally, we discuss agricultural systems designed for space, focusing on Bioregenerative Life Support Systems (BLSS), the selection and breeding of plants suited for space, and their potential applications. Finally, we highlight the challenges and future research directions in plant biology and space agricultural systems.

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.

Spaceflight has an impact on the growth and development of higher plants at both the vegetative stage and reproductive stage. A great deal of information has been available on the vegetative stage in space, but relatively little is known about the influence of spaceflight on plants at the reproductive stage. In this study, we constructed transgenic Arabidopsis thaliana plants expressing the flowering control gene, FLOWERING LOCUS T (FT), together with the green fluorescent protein gene (GFP) under control of a heat shock-inducible promoter (HSP17.4), by which we induced FT expression inflight through remote controlling heat shock (HS) treatment. Inflight photography data showed that induction of FT expression in transgenic plants in space under non-inductive short-day conditions could promote flowering and reduce the length of the inflorescence stem in comparison with that of wild-type plants under the same conditions. Whole-genome microarray analysis of gene expression changes in leaves of wild-type and these transgenic plants grown under the long-day and short-day photoperiod conditions in space indicated that the function of the photoperiod-related spaceflight responsive genes is mainly involved in protein synthesis and post-translation protein modulation, notably protein phosphorylation. In addition, changes of the circadian component of gene expression in response to spaceflight under different photoperiods indicated that roles of the circadian oscillator could act as integrators of spaceflight response and photoperiodic signals in Arabidopsis plants grown in space.