Correct blue-light regulation of pea Lhcb genes in an Arabidopsis background.

Irradiation of etiolated Arabidopsis or pea, or dim-red-light-grown pea seedling with a single, short (under 10 s) pulse of blue light (threshold at 0.1 mumol/m2) is sufficient to induce the expression of specific members of the Lhcb gene family including the pea Lhcb1*4 gene and the Arabidopsis Lhcb1*3 gene. Other Lhcb genes, such as the pea Lhcb1*3 gene and the Arabidopsis Lhcb1*1 and 1*2 genes are unaffected by this blue-light treatment. Transgenic Arabidopsis bearing pea Lhcb1*3::Gus (beta-glucuronidase), pea Lhcb1*4::Gus or Arabidopsis Lhcb1*3::Gus constructs were used to determine if pea and Arabidopsis employ a similar mechanism to achieve blue-light induced Lhcb expression. Examination of the respective Gus expression patterns in white-light-grown seedlings indicates that the pea promoters are active and properly expressed in the Arabidopsis background. Irradiation of dark-grown Arabidopsis with a 20 s pulse of blue light with a total fluence of 100 mumol/m-2 results in expression of the pea Lhcb1*4::Gus (beta-glucuronidase) construct, but not of the pea Lhcb1*3::Gus construct indicating that the pea promoters respond correctly to blue light in the Arabidopsis background. Fluence-response, time-course and reciprocity characteristics for the blue-light-induced expression of the pea Lhcb1*4::Gus construct closely resemble those of the endogenous Arabidopsis Lhcb genes, confirming the proper interpretation of the Arabidopsis blue-light-signaling mechanism by the pea Lhcb1*4 promoter and suggesting that the signaling mechanisms in the two plants are very similar, if not identical. Fluence response data for the steady-state level of transcript derived from an Arabidopsis Lhcb1*3::Gus construct extending 200 bp upstream of the site of transcription indicate that the blue light responsive elements(s) are contained within this 200 bp region.