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Development and characterization of bathochromic phytochrome mutants
Phytochromes are red/far-red photoreceptors that mediate a variety of photomorphogenic processes in plants including germination, shade avoidance, and flowering. Phytochromes are dimeric chromopeptides and have two spectral photoisomers, the red-light absorbing Pr and far-red light absorbing Pfr forms. In nature, phytochromes recognize the ratio of red and far-red light (R: FR ratio) from incoming light, changing the photoequilibrium of the Pr and Pfr forms to induce light responses. The aim of this study was to develop and characterize the in vivo function of bathochromic mutant phytochromes whose Pr-absorption spectra move to longer wavelength so that they can be activated even at low R: FR ratios to suppress shade avoidance in plants. ^ Photochromism of phytochromes is based on an intimate interaction between the chromophore and the protein moiety. Thus, the bathochromic mutants were developed by changing highly conserved amino acid residues in the bilin lyase domain of oat (Avena) phytochrome A. From the photochemical characterization of purified phytochrome mutants, several absorption wavelength-shifted mutants were obtained, including the bathochromic mutants, F389A with a 6 nm shift, F307R/C371A with an 8 nm shift and F307W/Y385A/F389A with a 12 nm shift, as well as hypsochromic mutants including R317E with an 8 nm shift. These data indicate that absorption maxima of phytochromes could be modified by changing the interaction between the chromophore and the amino acid residues in the chromophore-binding region. ^ Selected bathochromic phytochrome genes were introduced into phyA-deficient Arabidopsis. Using Arabidopsis transgenic plants, tolerance to shade was examined in both seedlings and adult plants under different shaded conditions. The transgenic Arabidopsis with bathochromic phytochromes displayed a suppression of hypocotyl elongation in seedlings under shaded conditions, and exhibited leaf morphologies indicative of shade tolerance in adult plants. Furthermore, plants expressing the 8-nm bathochromic phytochrome showed a greater degree of shade tolerance than those expressing the 6-nm bathochromic phytochrome (270% vs. 220% compared to wild-type Col-0 plants). In addition, floral initiation mediated by shade avoidance responses under FR enriched white light was suppressed by the bathochromic phytochromes. In comparison, transgenic plants with a hypsochromic mutant displayed an increased sensitivity to shade. These results indicate that shade avoidance responses can be effectively suppressed by bathochromic phytochromes. Since shade avoidance is second only to disease as a cause of crop-yield losses, the bathochromic phytochromes will be used to develop shade tolerant plants providing increased crop yields. ^
Kim, Yunjeong H, "Development and characterization of bathochromic phytochrome mutants" (2005). ETD collection for University of Nebraska - Lincoln. AAI3163993.