Figure 8.

Summary model of RAP2.12 regulation of plant metabolism based on the results of this work. When oxygen falls to concentrations below 10% (v/v), the transcription factor RAP2.12 is stabilized and moves to the nucleus to activate the expression of specific genes (Kosmacz et al., 2015). First, mRNA levels and enzyme activities of AlaAT are increased, resulting in increased levels of Ala and γ-amino butyrate and associated changes in the flux modus of the TCA cycle, including an inhibition of succinate dehydrogenase, which finally leads to an inhibition of respiration. The precise mechanism of RAP2.12 regulation of AlaAT expression has not been clarified yet. Second, mRNA levels and enzyme activities of ADH, PDC, and LDH are increased, resulting in elevated rates of ethanol and lactate fermentation. In Arabidopsis plants overexpressing a deregulated (constitutively stabilized) RAP2.12, these metabolic changes are also observed under normoxic conditions, leading to decreased growth and anoxic stress resistance. Green = promoting effects; red = inhibiting effects; dotted arrow = precise mechanism is not known yet.