A Ca2+/calmodulin-binding peroxidase from Euphorbia latex: novel aspects of calcium-hydrogen peroxide cross-talk in the regulation of plant defenses.
Calmodulin (CaM) is a ubiquitous Ca(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(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(2+)/CaM-activated proteins are known to tune the interaction between calcium and H(2)O(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(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(2+)/H(2)O(2)-mediated plant defense system, having both positive and negative effects in regulating H(2)O(2) homeostasis.
Mura
Anna
A
Department of Applied Sciences in Biosystems, University of Cagliari, 09042 Monserrato, Cagliari, Italy.
Medda
Rosaria
R
Longu
Silvia
S
Floris
Giovanni
G
Rinaldi
Andrea C
AC
Padiglia
Alessandra
A
D000595:Amino Acid Sequence; D001483:Base Sequence; D002118:Calcium / Q000494:pharmacology*; D002147:Calmodulin / Q000378:metabolism*; D002148:Calmodulin-Binding Proteins / Q000235:genetics / Q000378:metabolism; D002413:Cations, Divalent; D004591:Electrophoresis, Polyacrylamide Gel; D028481:Euphorbia / Q000201:enzymology*; D018506:Gene Expression Regulation, Plant / Q000187:drug effects*; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D008969:Molecular Sequence Data; D009195:Peroxidase / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D015398:Signal Transduction
D002147:Calmodulin; D002148:Calmodulin-Binding Proteins; D002413:Cations, Divalent; D006861:Hydrogen Peroxide; D009195:Peroxidase; D002118:Calcium