Figure 12.

Illustration of the hypothetical mechanism proposed about the role of the MAPK cascade in the regulation of nitrate reductase. The different N sources (orange ray) would activate a MAPK signaling cascade that would ultimately cause the phosphorylation of NR, probably in the hinge region 2. This would activate/inhibit the binding of NOFNiR or THB1, which would control the reduction of nitrite to NO, and would act as a signaling molecule. With our data we propose RAF14 and RAF79 as candidates to sense the N signal. The question mark indicates that such interactions have not been experimentally demonstrated yet. The dotted arrows represent the movement of electrons and the solid arrows the substrate and product of each protein.