Regulatory elements for light-dependent and organ-specific expression of Arabidopsis thaliana PSBO1 gene encoding 33Â kDa polypeptide of the oxygen-evolving complex

The 33 kDa polypeptide of the oxygen-evolving complex in Arabidopsis is encoded by two paralogous genes, PSBO1 and PSBO2 (located on chromosomes 5 and 3, respectively), which show 80.35% homology at the nucleotide level, 95.18% homology at the protein level and conservation of a large number of cis-regulatory elements within −500 bp from the translational start site. Mapping of the transcription start site revealed that PSBO1 has a 45 bp long leader sequence. The expression of PSBO1 and PSBO2 is tissue-specific and is stimulated by light in both young and mature plants of Arabidopsis. However, the transcript for PSBO1 accumulates at higher level than PSBO2. To define the regulatory elements, four deletion constructs, designed from the upstream sequence of the PSBO1 gene and the 2.7 kb promoter, fused with GUS, were mobilized in tobacco and the T0 transgenics as well as the progeny analyzed for light-inducibility and organ-specific expression. Promoter-deletion analysis revealed that the regulatory elements conferring light-responsivity reside within −165 bp of the translational start site. The existence of some positive regulatory elements in the region between −165 and −570 bp has also been unravelled.