Light controls phospholipase A2α and β gene expression in Citrus sinensis

The low-molecular weight secretory phospholipase A(2)alpha (CssPLA(2)alpha) and beta (CsPLA(2)beta) cloned in this study exhibited diurnal rhythmicity in leaf tissue of Citrus sinensis. Only CssPLA(2)alpha displayed distinct diurnal patterns in fruit tissues. CssPLA(2)alpha and CsPLA(2)beta diurnal expression exhibited periods of approximately 24 h; CssPLA(2)alpha amplitude averaged 990-fold in the leaf blades from field-grown trees, whereas CsPLA(2)beta amplitude averaged 6.4-fold. Diurnal oscillation of CssPLA(2)alpha and CsPLA(2)beta gene expression in the growth chamber experiments was markedly dampened 24 h after transfer to continuous light or dark conditions. CssPLA(2)alpha and CsPLA(2)beta expressions were redundantly mediated by blue, green, red and red/far-red light, but blue light was a major factor affecting CssPLA(2)alpha and CsPLA(2)beta expression. Total and low molecular weight CsPLA(2) enzyme activity closely followed diurnal changes in CssPLA(2)alpha transcript expression in leaf blades of seedlings treated with low intensity blue light (24 mu mol m(-2) s(-1)). Compared with CssPLA(2)alpha basal expression, CsPLA(2)beta 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.