Circadian and phytochrome control act at different promoter regions of the tomato Lhca3 gene

The expression of the Lhc genes is influenced by external (e.g. light, temperature) and endogenous (e.g. circadian clock) factors and processes. Their signal transduction pathways are integrated in a complex regulatory network. The action of an endogenous clock is only useful if it can be synchronized by external factors, most importantly by light. Therefore, overlapping effects of the circadian system and light perception signal transduction chain are expected. Since exclusive phytochrome or circadian clock control has not been shown, it was hypothesized that both signal transduction pathways converge in one transcription complex using the same cis-regulatory element (Anderson et al. 1994). However, here we present for the first time evidence that different promoter regions are sufficient to mediate phytochrome or circadian control. While the Δ-278 and Δ-231 promoter deletion lines of the tomato Lhca3 gene can both be activated by red light and reversed by far red light pulses, only the Δ-278 deletion revealed transcript oscillations, indicating that 231 bp are sufficient mediating phytochrome control while 278 bp are needed for circadian expression.