Expression of a functional monocotyledonous phytochrome in transgenic tobacco

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Abstract
A chimeric oat phytochrome structural gene with an uninterrupted coding region was constructed for expression of the monocot protein in transgenic plants. The structural gene was placed under the transcriptional control of either a light‐regulated oat phytochrome promoter or the constitutively active cauliflower mosaic virus 35S promoter. These genes were then introduced into Nicotiana tabacum and N.plumbaginifolia. None of the regenerated plants showed expression of oat phytochrome RNA when transcription was controlled by the oat promoter. In contrast, RNA was obtained in plants when the structural gene was functionally linked to the 35S promoter. Transformants expressing oat phytochrome RNA produced a full length 124‐kd polypeptide that was recognized by oat‐specific anti‐phytochrome monoclonal antibodies. The oat protein was a substrate for chromophore addition in tobacco as judged by its red/far‐red photoreversible sensitivity to trypsin degradation. Production of oat phytochrome in transgenic plants gave rise to increased phytochrome spectral activity in both light‐ and dark‐grown plants. This increased phytochrome content resulted in phenotypic changes in transformed plants, including semi‐dwarfism, darker green leaves, increased tillering and reduced apical dominance. The possible significance of expressing a biologically active phytochrome in transgenic plants is discussed.