Overexpression of rice phytochrome A in tobacco seedlings modifies responsiveness but not competence to phytochrome

Abstract

Abstract.To analyse the control of rice phytochrome A (phyA) overexpression (wild type or variously mutated) on gene regulation, transgenic tobacco lines overexpressing various rice phyA constructs were crossed with transgenic tobacco lines containing mustard Lhcbl or Chsl promoters fused to the uidA reporter gene (13-glucuronidase). It was demonstrated that the temporal pattern of competence to respond to phytochrome was not altered by rice phyA overexpression. Also, overexpression of rice phyA did not change the spatial pattern of gene expression. The responsiveness to red and far-red light, on the other hand, depended on the type of overexpressed rice phyA in a structure-function relation: the serine-to-alanine mutant mediated an enhanced response both under continuous red and far-red light, whereas the N-terminal deletion mutant showed a dominant negative effect under continuous far-red light and even after red light pulses. However, the effectiveness of rice phyA overexpression depended on the promoter construct and the developmental stage of the seedlings. The Lhcbl promoter also conferred 13-glucuronidase activity in etiolated seedlings. This dark expression could be decreased by a long-wavelength farred light pulse given early in development (24 h after sowing), indicating that this phenomenon is under the control of stable types of phytochrome.

Maternal Effect on Embryogenesis in Tobacco Overexpressing Rice Phytochrome A*

“…Hypocotyl elongation and reporter gene expression demonstrated that RW and S/A overexpression leads to enhancement, whereas NTD overexpression causes a suppression of phyA responses (Emmler et al. 1995(Emmler et al. , 1996Stockhaus et al, 1992).…”

“…Crossing experiments were performed with plants of the tobacco cultivar SRl bearing promoter GUS reporter genes. These crossings were initiated by a different study where the influence of rice PHYA overexpression on reporter gene expression had been analyzed (Emmler et al, 1996). For the production of seedlings with fused cotyledons, F1 plants from crossings between SR1 pollen acceptors and rice PHYA overexpressor pollen donors were grown to maturity.…”

“…Deletion of the amino-terminal end of the overexpressed phyA has inhibited the function of the endogenous phyA (Boylan et al. 1994: Emmler et al, 1995,1996.…”

“…On the other hand, substitution of the first ten serines by alanines in the amino acid sequence of the overexpressed phyA has led to hyperactivity (Stockhaus et al, 1992: Emmler et al, 1995,1996.…”

Fundamental and biotechnological applications of phytochrome transgenes

“…Endogenous tobacco phyA appears to play little if any role in hook opening and therefore in this instance, although heterologous phyA is able to function in hook opening, it is unlikely to reflect the activity of endogenous protein . Transgenically produced rice phyA does, however, induce the same temporal and spatial pattern of expression from Lhcbl and Chsl promoters as does endogenous phyA (Emmler et al 1996). Therefore, the activity of rice phyA in hook opening may reflect a true but relatively small activity of endogenous phyA, or reflect a fundamental difference between monocot and dicot phytochromes in regulating hook opening.…”