Researchers have been studying transcriptomic and proteomic responses of plants to ranges of reduced gravitational conditions. These include blue and red light in microgravity, circadian rhythms in microgravity, microgravity in different ecotypes, microgravity on suborbital flights, and they have using a variety of experimental equipment. Recent findings have linked microgravity and transcriptomic changes in genes relating to cell wall synthesis and modification, oxidative stress, abiotic stressors, phytohormones, sugar synthesis and metabolism, ribosomal biogenesis, and plant defense to other organisms. Although we have a better-established profile of the transcriptomic response of plants to reduced gravity, some areas of study have not yet been thoroughly investigated. The initial stages and progression of transcriptional responses to microgravity, the responses of additional plant species, and tissue-specific transcriptional responses to microgravity should all be further investigated in order to better develop our understanding of how plants react to a reduced gravity environment. In the near future, advancing technology, rapidly growing databases, and an increasing number of spaceflight opportunities will allow for more research to be conducted to address these and many other related questions in plant space biology.

Cytokinin Response Factors (CRFs) are transcription factors that are involved in cytokinin (CK) response, as well as linked to abiotic stress tolerance. In particular, oxidative stress responses are activated by Clade III CRF members, such as AtCRF6. Here we explored relationships between Clade III CRFs and oxidative stress. Transcriptomic responses to oxidative stress were determined in two Clade III transcription factors, Arabidopsis AtCRF5 and tomato SlCRF5. AtCRF5 was required for regulated expression of over 240 genes involved that are involved in oxidative stress response. Similarly, SlCRF5 was involved in the regulated expression of nearly 420 oxidative stress response genes. Similarities in gene regulation by these Clade III members to oxidative stress were observed between Arabidopsis and tomato, as indicated by GO term enrichment. CK levels were also changed in response to oxidative stress in both species. These changes were regulated by Clade III CRFs. Taken together, these findings suggest that Clade III CRFs play a role in oxidative stress response as well as their roles in CK signaling.

Cytokinin (CK) is a plant hormone crucial to plant development and growth. Cytokinin Response Factor 6 (CRF6) is a CK‐induced transcription factor that is part of the CK signaling cascade. While the role of CRF6 has been examined in oxidative stress response, there has been surprisingly little investigation of CRF6 in the context of CK signaling, including identifying CK‐regulated targets of CRF6. Here, we conduct a transcriptomic study of Arabidopsis examining the CRF6 mutant (crf6) in the presence and absence of CK, revealing 163 downstream CRF6‐dependent CK‐regulated differentially expressed genes (DEGs). 15.3% of these DEGS were found as overlapping with larger number of standardly identified CK‐regulated DEGs, suggesting that CRF6 is involved in regulating a subset of downstream CK responses through these gene targets. The general transcriptional regulation of CRF6‐dependent CK‐regulated DEGs indicates that CRF6 may function as a negative regulator of CK response. We investigated one subset of CRF6 CK‐dependent targets (SKOR, HAK5, and NRT1. 5) involved in an underexamined functional role of CK response: the uptake and transportation of potassium. To determine how CK and CRF6 are involved in potassium acquisition and distribution, ionomic and physiological experiments were conducted on plants grown in media with sufficient and deficient potassium concentrations and in the presence and absence of CK. In order to investigate how CK alone affects potassium transport, similar experiments were performed on skor, hak5, and nrt1.5 mutant lines of these CRF6‐dependent CK‐regulated targets. These findings indicate novel connections between CK and potassium transport, which appear to be regulated in a CRF6‐dependent manner.

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