A Ca super(2+)/Calmodulin-Binding Peroxidase from Euphorbia Latex: Novel Aspects of Calcium-Hydrogen Peroxide Cross-Talk in the Regulation of Plant Defenses

• Published in: Biochemistry (Easton) 2005-11, Vol.44 (43), p.14120-14130
• Main Authors: Mura, A, Medda, R, Longu, S, Floris, G, Rinaldi, A C, Padiglia, A
• Format: Article
• Language: English
• Subjects: Euphorbia characias
• ISSN: 0006-2960
• DOI: 10.1021/bi0513251

Calmodulin (CaM) is a ubiquitous Ca super(2+) sensor found in all eukaryotes, where it participates in the regulation of diverse calcium-dependent physiological processes. In response to fluctuations of the intracellular concentration of Ca super(2+), CaM binds to a set of unrelated target proteins and modulates their activity. In plants, a growing number of CaM-binding proteins have been identified that apparently do not have a counterpart in animals. Some of these plant-specific Ca super(2+)/CaM-activated proteins are known to tune the interaction between calcium and H sub(2)O sub(2) in orchestrating plant defenses against biotic and abiotic stresses. We previously characterized a calcium-dependent peroxidase isolated from the latex of the Mediterranean shrub Euphorbia characias (ELP) [Medda et al. (2003) Biochemistry 42, 8909-8918]. Here we report the cDNA nucleotide sequence of Euphorbia latex peroxidase, showing that the derived protein has two distinct amino acid sequences recognized as CaM-binding sites. The cDNA encoding for an E. characias CaM was also found and sequenced, and its protein product was detected in the latex. Results obtained from different CaM-binding assays and the determination of steady-state parameters showed unequivocally that ELP is a CaM-binding protein activated by the Ca super(2+)/CaM system. To the best of our knowledge, this is the first example of a peroxidase regulated by this classic signal transduction mechanism. These findings suggest that peroxidase might be another node in the Ca super(2+)/H sub(2)O sub(2)-mediated plant defense system, having both positive and negative effects in regulating H sub(2)O sub(2) homeostasis.