Rewiring of primary metabolism for ammonium recycling under short-term low CO treatment - its implication for C evolution.

The dramatic decrease in atmospheric CO concentration during Oligocene was proposed as directly linked to C evolution. However, it remains unclear how the decreased CO concentration directly facilitate C evolution, besides its role as a selection pressure. We conducted a systematic transcriptomics and metabolomics analysis under short-term low CO condition and found that grown under this condition showed 1) increased expression of most genes encoding C-related enzymes and transporters; 2) increased expression of genes involved in photorespiration and pathways related to carbon skeleton generation for ammonium refixation; 3) increased expression of genes directly involved in ammonium refixation. Furthermore, we found that treatment of leaves with NH induced a similar pattern of changes in C related genes and genes involved in ammonium refixation. These data support the view that grown under short-term low CO conditions rewired its metabolism to supply carbon skeleton for ammonium recycling, during which process the expression of C genes were up-regulated as a result of a hitchhiking process. This study provides new insights into the adaptation of the C model plant under low CO conditions and suggests that low CO can facilitate the evolution of C photosynthesis beyond the commonly assumed role of being a selection pressure.