Light controls phospholipase A(2)α and β gene expression in Citrus sinensis

The low-molecular weight secretory phospholipase A(2)α (CssPLA(2)α) and β (CsPLA(2)β) cloned in this study exhibited diurnal rhythmicity in leaf tissue of Citrus sinensis. Only CssPLA(2)α displayed distinct diurnal patterns in fruit tissues. CssPLA(2)α and CsPLA(2)β diurnal expression exhibited periods of approximately 24 h; CssPLA(2)α amplitude averaged 990-fold in the leaf blades from field-grown trees, whereas CsPLA(2)β amplitude averaged 6.4-fold. Diurnal oscillation of CssPLA(2)α and CsPLA(2)β gene expression in the growth chamber experiments was markedly dampened 24 h after transfer to continuous light or dark conditions. CssPLA(2)α and CsPLA(2)β expressions were redundantly mediated by blue, green, red and red/far-red light, but blue light was a major factor affecting CssPLA(2)α and CsPLA(2)β expression. Total and low molecular weight CsPLA(2) enzyme activity closely followed diurnal changes in CssPLA(2)α transcript expression in leaf blades of seedlings treated with low intensity blue light (24 μmol m(−2) s(−1)). Compared with CssPLA(2)α basal expression, CsPLA(2)β expression was at least 10-fold higher. Diurnal fluctuation and light regulation of PLA(2) gene expression and enzyme activity in citrus leaf and fruit tissues suggests that accompanying diurnal changes in lipophilic second messengers participate in the regulation of physiological processes associated with phospholipase A(2) action.