Nitric oxide mediates iron induction of ferritin accumulation in Arabidopsis thaliana

Nitric oxide (NO) is a signaling molecule that plays a critical role in the activation of innate immune and inflammatory responses in animals. During the last few years, NO has also been detected in several plant species and the increasing number of reports on its function in plants have implicated NO as an important effector of growth, development, and defense. We investigated the possible role of NO as regulator of iron homeostasis in plant cells, in particular its involvement in the regulation of A.thaliana ferritin, an iron-storage protein which accumulates in response to iron increase. The infiltration of the NO-donor sodium nitroprusside (SNP) in Arabidopsis leaves induces accumulation of ferritin both at mRNA and protein level. Iron is not necessary for this NO-mediated ferritin transcript accumulation, since SNP is still able to induce the accumulation of ferritin transcript in Arabidopsis suspension cultures pretreated with the iron chelants DFO or ferrozine. However, NO is required for iron-induced ferritin accumulation, as the NO scavenger CPTIO prevents ferritin transcript accumulation in Arabidopsis suspension cultures treated with iron. The pathway is ser/thr phosphatase-dependent, necessitates protein synthesis and is cGMP independent. Most important, NO mediates ferritin regulation through the IDRS sequence of the Atfer1 promoter responsible for transcriptional repression under low iron supply. NO, by acting downstream of iron in the induction of ferritin transcript accumulation is therefore a key signaling molecule for regulation of iron homeostasis in plants