T. Xing et al., Ectopic expression of an Arabidopsis calmodulin-like domain protein kinase-enhanced NADPH oxidase activity and oxidative burst in tomato protoplasts, MOL PL MICR, 14(10), 2001, pp. 1261-1264
Among plant defense responses to pathogen attack, the release of active oxy
gen species (AOS), termed the oxidative burst, may affect the attacking pat
hogen and the host plant cells at the infection site, thereby limiting the
spread of the pathogen. Plasma membrane-associated NADPH oxidase represents
a key enzyme in mediating the oxidative burst. The mechanisms of NADPH oxi
dase activation, however, remains unclear. Ectopic expression of AK1-6H, an
Arabidopsis calmodulin-like domain protein kinase (CDPK) in tomato protopl
asts enhanced plasma membrane-associated NADPH oxidase activity. Arabidopsi
s protein phosphatase 2A abolished this enhancement, whereas Arabidopsis du
al-specificity protein tyrosine phosphatase 1 or maize protein phosphatase
1 had no effect. tMEK2(MUT), a constitutively activated, mitogen-activated
protein kinase kinase from tomato, did not enhance NADPH oxidase activity w
hen overexpressed. In a cell-free system, AK1-6H moderately stimulated the
NADPH oxidase activity on plasma membrane. AK1-6H, but not tMEK2(MUT), also
enhanced production of AOS in Intact protoplasts. Our results show that ec
topic expression of a heterologous CDPK can enhance NADPH oxidase activity
and stimulate an oxidative burst in tomato protoplasts.