Abstract
It is widely accepted that atmospheric O2 has played a key role in the development of life on Earth, as evident from the coincidence between the rise of atmospheric O2 concentrations in the Precambrian and biological evolution. Additionally, it has also been suggested that low atmospheric O2 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 O2 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 O2 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 O2 conditions (576 genes). Intriguingly, the expression of comparatively fewer numbers of genes (411 genes) was affected under a combination of both sub-ambient O2 and elevated CO2 condition (low O2-high CO2). Overall, the results point towards the effects of atmospheric changes in CO2 and O2 on transcriptional reprogramming, photosynthetic regulation, carbon metabolism, and stress responses.
Highlights
The moss Physcomitrella patens is a non-vascular, multicellular land plant believed to have diverged from the land plant lineage more than 400 million years ago (Nishiyama et al, 2003)
Microarray analysis revealed that the expression of a large number of genes (n = 814, fold change ≥ 2; P < 0.05), relative to ambient conditions, were significantly affected when P. patens gametophytes were grown under elevated CO2 conditions
Of the 814 genes significantly affected under elevated CO2, 63% were up-regulated, whereas only 45% and 54% of the transcripts were up-regulated in response to sub-ambient O2, and low O2–high CO2 treatment, respectively (Fig. 1A)
Summary
The moss Physcomitrella patens is a non-vascular, multicellular land plant believed to have diverged from the land plant lineage more than 400 million years ago (Nishiyama et al, 2003). P. patens has a relatively simple morphology and single-celled layer anatomy, thereby requiring constant co-equilibration of tissue water content with the environment (Reski, 1999; Quatrano et al, 2007; Charron and Quatrano, 2009; Cho et al, 2009) Such simple anatomical features imply the evolution of considerable intrinsic cellular and molecular mechanisms in response to abiotic stresses, and there is evidence to suggest that P. patens is highly tolerant of abiotic stresses (Frank et al, 2005; Cho et al, 2009; Mishler and Oliver, 2009; Koster et al, 2010). It has been suggested that low atmospheric O2 is one of the major drivers for at least two of the five mass-extinction events in the Phanerozoic (Lenton, 2003; Huey and Ward, 2005)
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