Genome-wide transcriptomic analysis of the effects of sub-ambient atmospheric oxygen and elevated atmospheric carbon dioxide levels on gametophytes of the moss, Physcomitrella patens

It is widely accepted that atmospheric O-2 has played a key role in the development of life on Earth, as evident from the coincidence between the rise of atmospheric O-2 concentrations in the Precambrian and biological evolution. Additionally, it has also been suggested that low atmospheric O-2 is one of the major drivers for at least two of the five mass-extinction events in the Phanerozoic. At the molecular level, our understanding of the responses of plants to sub-ambient O-2 concentrations is largely confined to studies of the responses of underground organs, e.g. roots to hypoxic conditions. Oxygen deprivation often results in elevated CO2 levels, particularly under waterlogged conditions, due to slower gas diffusion in water compared to air. In this study, changes in the transcriptome of gametophytes of the moss Physcomitrella patens arising from exposure to sub-ambient O-2 of 13% (oxygen deprivation) and elevated CO2 (1500 ppmV) were examined to further our understanding of the responses of lower plants to changes in atmospheric gaseous composition. Microarray analyses revealed that the expression of a large number of genes was affected under elevated CO2 (814 genes) and sub-ambient O-2 conditions (576 genes). Intriguingly, the expression of comparatively fewer numbers of genes (411 genes) was affected under a combination of both sub-ambient O-2 and elevated CO2 condition (low O-2-high CO2). Overall, the results point towards the effects of atmospheric changes in CO2 and O-2 on transcriptional reprogramming, photosynthetic regulation, carbon metabolism, and stress responses.