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.

Efficient in vitro callus generation is required for tissue culture propagation, a process that allows for plant regeneration and transgenic breeding for desired phenotypes. Identifying genes and regulatory elements that prevent impaired callus growth and callus browning is essential for the development of in vitro callus systems. Here, we show that the BREVIPEDICELLUS (BP) and ERECTA (ER) pathways in Arabidopsis calli converge to prevent callus browning and positively regulate the expression of the isoperoxidase gene AtPRX17 in rapidly growing calli. Loss-of-function mutations in both BP and ER resulted in markedly increased callus browning. Transgenic lines expressing 35S pro::AtPRX17 in the bp-5 er105 double mutant background fully rescued this phenotypic abnormality. Using in vivo assays (chromatin immunoprecipitation-PCR and transient expression) and in vitro assays (electrophoretic mobility shift assays), we observed that the BP protein binds directly to the upstream sequence of AtPRX17 to promote its transcription during callus growth. ER is ubiquitous factor required for cell proliferation and growth. We show that ER positively regulates the expression of the transcription factor WRKY6, which directly binds to a separate site on the AtPRX17 promoter, further increasing its expression. Our data reveal an important molecular mechanism involved in the regulation of peroxidase isozyme expression to reduce Arabidopsis callus browning.