Expression of functional oat phytochrome A in transgenic rice.
To investigate the biological functions of phytochromes in monocots, we generated, by electric discharge particle bombardment, transgenic rice (Oryza sativa cv Gulfmont) that constitutively expresses the oat phytochrome A apoprotein. The introduced 124-kD polypeptide bound chromophore and assembled into a red- and far-red-light-photoreversible chromoprotein with absorbance spectra indistinguishable from those of phytochrome purified from etiolated oats. Transgenic lines expressed up to 3 and 4 times more spectrophotometrically detectable phytochrome than wild-type plants in etiolated and green seedlings, respectively. Upon photo-conversion to the far-red-absorbing form of phytochrome, oat phytochrome A was degraded in etiolated seedlings with kinetics similar to those of endogenous rice phytochromes (half-life approximately 20 min). Although plants overexpressing phytochrome A were phenotypically indistinguishable from wild-type plants when grown under high-fluence white light, they were more sensitive as etiolated seedlings to light pulses that established very low phytochrome equilibria. This indicates that the introduced oat phytochrome A was biologically active. Thus, rice ectopically expressing PHY genes may offer a useful model to help understand the physiological functions of the various phytochrome isoforms in monocotyledonous plants.
Clough
R C
RC
Department of Horticulature, University of Wisconsin-Madison 53706, USA.
Casal
J J
JJ
Jordan
E T
ET
Christou
P
P
Vierstra
R D
RD
D018554:Avena / Q000235:genetics*; D018548:Cotyledon / Q000528:radiation effects; D017343:Genes, Plant; D015151:Immunoblotting; D007700:Kinetics; D008027:Light; D012275:Oryza / Q000235:genetics / Q000254:growth & development / Q000378:metabolism* / Q000528:radiation effects; D010641:Phenotype; D010834:Phytochrome / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D051942:Phytochrome A; D018547:Plant Stems / Q000528:radiation effects; D030821:Plants, Genetically Modified / Q000378:metabolism; D013053:Spectrophotometry
D051942:Phytochrome A; D010834:Phytochrome