Expression of Functional Oat Phytochrome A in Transgenic Rice

Abstract

To investigate the biological functions of phytochromes in monocots, we generated, by electric discharge particle bombardment, transgenic rice (Oryza sativa cv Culfmont) that constitutively expresses the oat phytochrome A apoprotein. l h e introduced 124-kD polypeptide bound chromophore and assembled into a red-and far-red-light-photoreversible chromoprotein with absorbance spectra índistinguishable 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 photoconversion 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. lhis 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.

Map-Based Cloning of the Gene Associated With the Soybean Maturity Locus E3

“…The phyA mutant in rice displayed insensitivity to FR light in etiolated seedlings, but showed no significant differences from the wild type when grown under natural daylength conditions (Takano et al 2001). Moreover, overexpression of oat PhyA in transgenic rice showed no differences from the wild-type rice plants (Clough et al 1995). Nevertheless, combinations of other phytochrome mutants could dramatically alter the flowering time.…”

Photoresponses of Transgenic Arabidopsis Overexpressing the Fern Adiantum capillus-veneris PHY1

“…This result is in contrast to those obtained with angiosperm phytochromes. Overexpression of either phyA (Boylan and Quail, 1991;Nagatani et al, 1991;Clough et al, 1995) or phyB (Wagner et al, 1991) results in a dwarf phenotype under continuous R and/or FR. Although Adiantum PHY1 shows equal similarity to a11 angiosperm phytochromes, it has two stretches of sequences, motif 1 and motif 2, that are conserved among different PHYB sequences but are not found in other angiosperm PHY sequences (Okamoto et al, 1993).…”

Photoreceptor Biotechnology

“…When extra copies of the native tobacco phyA gene are introduced into tobacco under the control of the same promoter, the phenotype generated is much more subtle (Hudson, 1997). The effect of oat phyA overexpression in rice or wheat is marginal (Clough et al, 1995, Schlumukhov et al, 2003. Conversely, the introduction of an Arabidopsis PHYA gene into rice causes significant dwarfing and the promise of substantial increase in yield (Garg et al, 2005).…”

“…However, improved transformation technologies have led to phytochrome overexpression being applied in rice (Clough et al, 1995, Garg et al, 2005 and wheat (Schlumukhov et al, 2003).…”

“…Significant alteration of yield or morphology has not yet been accomplished by means of Avena PHYA introduced into rice or wheat (Clough et al, 1995, Schlumukhov et al, 2003. However, Arabidopsis PHYA overexpression in aromatic rice (Oryza sativa L. Pusa Basmati-1) has been demonstrated to create a strong dwarfing phenotype, including reduction in plant height, reduction in internode length and diameter, and an increase in panicle number (Figure 1, Garg et al, 2005).…”