Plant development on ISS differes from the development on the ground and is influenced by the genetic background.

The development of Col-0 and WS plants on orbit differs from that on the ground as demonstrated by the comparison of the gene expression profiles between 4 days old to 8 days old plant in the two environments. The Col-0 plants used different genes reflecting different physiological processes than WS plants, suggesting the role of the genetic background in the developmental decisions. The 4 days old Col-0 plant in orbit showed deficit in wax and suberin production relatively to the 8 days old plants, the difference unregistered on the ground. There was more dramatic difference in the overexpression of the root system development and anatomical structure development genes in 8 days old plants than in 4 days old plant in both genotypes on the ground than in flight, implying smaller root developmental gap between 4 days and 8 days old roots in orbit. The WS plant uniquely showed overexpression of the photosynthesis related genes in the 4 days old roots relative to 8 days old root in the spaceflight environment but not on the ground. The seeds germinated in the novel growth environment of ISS implemented different developmental strategies as captured by the genes expression patterns, than seeds developing on the ground. Overall design: APEX03-2 (Advanced Plant Experiment 03-2) also identified as TAGES-Isa (Transgenic Arabidopsis Gene Expression System—Intracellular Signaling Architecture) was launched on SpaceX mission CRS-5 on 10 January 2015. Dry, sterilized Arabidopsis seeds were planted aseptically on the surface of 10-cm2 solid media plates and remained dormant until removed from cold stowage and exposed to light at the initiation of the experiment on the ISS (International Space Station). The plates were grown in the Vegetable Production System (VPS/Veggie) hardware on the Columbus Module of the ISS with the overhead LED lighting of the VPS. At four or for the second experimental set at eight days, seedlings were harvested by an astronaut into KFT (Kennedy Fixation Tube) containing RNAlater solutions. Upon return to Earth, the harvested material was used to compare the transcriptomes of each genotype and each age using RNAseq technology. The patterns of gene expression was compared between treatments (spaceflight versus ground control) within each genotype of same age or between two ages within same genotype and within same treatment. For 4 day old roots 5-8 roots were combined to serve as one biological replica. For 8 day old roots 2-3 roots were used to form one biological replica. In each case the four biological replicas were used for the transcriptomic analysis.

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