Nitric oxide modulates the activity of tobacco aconitase

Recent evidence suggests an important role for nitric oxide (NO) signaling in plant-pathogen interactions. Additional elucidation of the role of NO in plants will require identification of NO targets. Since aconitases are maj or NO targets in animals, we examined the effect of NO on tobacco (Nicotian a tabacum) aconitase. The tobacco aconitases, like their animal counterpart s, were inhibited by NO donors. The cytosolic aconitase in animals, in addi tion to being a key redox and NO sensor, is converted by NO into an mRNA bi nding protein (IRP, or iron-regulatory protein) that regulates iron homeost asis. A tobacco cytosolic aconitase gene (NtACO1) whose deduced amino acid sequence shared 61% identity and 76% similarity with the human IRP-1 was cl oned. Furthermore, residues involved in mRNA binding by IRP-1 were conserve d in NtACO1. These results reveal additional similarities between the NO si gnaling mechanisms used by plants and animals.