Transcriptional regulation of oscillating steady-state Lhc mRNA levels: Characterization of two Lhca promoter fragments in transgenic tobacco plants

Lhc genes from angiosperms display circadian steady-state mRNA oscillations as a result of differential transcriptional activation. We studied promote r regions of tomato Lhca genes encoding chloraphyll a/b binding proteins,wh ich are associated with photosystem I. Prornotrr deletion analysis showed t hat a 278 basepair (bp) DNA fragment from Lhca3 (cab 8) and a 119 bp fragme nt from Lhca4*1 (cab II) was sufficient to mediate circadian gene expressio n in transgenic plants. Further experiments using the GUS-reporter gene ass ay showed that an internal 110 bp DNA fragment cloned from the 278 bp regio n of Lhca3 (position -278 to -169), however, was not able to drive a circad ian reporter gene expression, indicating that additional cis-elements locat ed downstream or within the exons and introns of Lhca3 are necessary. In contrast, the 119 bp fragment of Lhca4*1 bears all elements sufficient f or a circadian mRNA accumulation pattern. The 119 bp promoter sequence of L hca4*1 contains imperfect repeats of the motif CAA(N2-4)ATC, which is prese nt in 81% of all published Lhc promoter regions. This sequence overlaps wit h a recently determined binding motif(AA(A)/(C)AATCT) of the circadianly re gulated transcription factor CCA1 isolated from Arabidopsis, suggesting tha t similar transcription factors may be involved in the circadian Lhc gene e xpression of angiosperms.