Establishment of far-red high irradiance responses in wheat through transgenic expression of an oat phytochrome A gene

A transgenic wheat line over-expressing an oat phytochrome A gene under the control of the constitutive maize ubiquitin promoter was generated using a biolistic particle delivery system from immature wheat embryos. The resulting line showed increased levels of total phytochrome A protein in both dark-grown and light-grown plants. When grown under continuous far-red light, seedlings of this line showed additional inhibition of the coleoptile extension in comparison with wild-type seedlings. Unlike the response of wild-type seedlings to continuous far-red, this additional inhibition was dependent on fluence rate and was not observed under half-hourly pulses of far-red delivering the same total fluence as the continuous irradiation treatment. These observations suggest that increase in phytochrome A levels in wheat leads to the establishment of a far-red high irradiation reaction in this monocotyledonous plant. Exposure to continuous red light caused a similar inhibition of coleoptile extension in both the wild types and the transgenic seedlings. When wild-type seedlings were grown under continuous far-red, their coleoptiles remained completely colourless and first leaves remained tightly rolled. In contrast, transgenic seedlings grown in the same conditions produced significant levels of anthocyanins in their coleoptiles and their first leaves became unrolled. Taken together, our data suggest that the increased levels of phytochrome A in wheat can change the type of response of some developmental processes to light signals, leading to the generation of a high irradiance reaction which is otherwise absent in the wild types under the conditions used.