Nucleotide Sequence of the psbP Gene Encoding Precursor of 23-kDa Polypeptide of Oxygen-Evolving Complex in Arabidopsis thaliana and its Expression in the Wild-Type and a Constitutively Photomorphogenic Mutant

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Abstract
The psbP gene encoding the precursor of 23-kDa polypeptide of the oxygen-evolving complex of photosystem II has been isolated from Arabidopsis thaliana genomic library and sequenced. The gene harbors three introns and encodes a mature polypeptide of 186 amino acid residues and a transit peptide of 77 amino acid residues. The deduced molecular mass of the mature polypeptide is 23.5 kDa and it contains 22.6% charged amino acid residues which may contribute to the hydrophilic nature of the protein. The transcript encoded by psbP gene of Arabidopsis is approximately 1.3 kb long. In wild-type Arabidopsis seedlings, its expresssion is organ-specific and is regulated by endogenous developmental cues, light and sucrose. In a constitutively photomorphogenic mutant of Arabidopsis , designated as pho1 , the psbP gene is partly derepressed in young, dark-grown seedlings, resulting in a slightly higher level of the transcript. Additionally, the pho1 mutant shows slow accumulation of psbP transcript upon illumination of young, dark-grown seedlings. However, the derepression is not markedly displayed on dark-adaptation of pho1 plants grown in continuous light. These studies, therefore, define the activity of at least one cellular effector involved in regulation of psbP expression.

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