Function of Phytochrome A in Potato Plants as Revealed through the Study of Transgenic Plants

Abstract

We have generated transgenic potato plants (Solanum fuberosum) containing the potato phytochrome protein encoded by the PHYA gene cDNA (phyA) in sense or antisense orientation under the control of the 35s cauliflower mosaic virus promoter. Plants with increased and decreased phyA levels were analyzed. When grown under white light, development and growth of sprouts and plants were barely distinguishable from wild type. Under continuous far-red light, stem extension, leaf expansion, and hook opening of sprouts were accelerated in phyA overexpressors and delayed in antisense plants. Sprouts with reduced phyA levels were less sensitive to red light with regard to stem extension and expression of the small subunit genes for ribulose bisphosphate carboxylase. Under low red 1ight:far-red light ratios, increased phyA levels reduced the stem extension component of the shade-avoidance response, whereas decreased levels led to an increase in the response.

The function of phytochrome A

“…At least in Arabidopsis, hypocotyl growth inhibition by FR is a HIR because it shows reciprocity failure (Mazzella et al 1997). Overexpression of oat phyA in transgenic tobacco (McCormac et al 1991), Arabidopsis (Whitelam et al 1992) and rice (Casal, Clough & Vierstra 1996), rice phyA in transgenic tobacco (Emmler et al 1995) and potato phyA in transgenic potato (Heyer et al 1995) enhances the response to continuous FR. Neither Arabidopsis nor rice phyB overexpressed in transgenic Arabidopsis appears to enhance HIR (McCormac era/.…”

“…The phyA mutants of Arabidopsis thaliana (Dehesh et al 1993; Nagatani, Reed & Chory 1993b; Whitelam et al 1993) or tomato (van Tuinen et al 1995) and transgenic potato plants expressing an anti-sense PHYA gene (Heyer et al 1995) fail to de-etiolate under continuous FR. At least in Arabidopsis, hypocotyl growth inhibition by FR is a HIR because it shows reciprocity failure (Mazzella et al 1997).…”

Regulation of Transcript Levels of a Potato Gibberellin 20-Oxidase Gene by Light and Phytochrome B

“…To assess the potential involvement of PHYA, we used potato plants (cv Désirée) that are antisensed for the PHYA gene (Heyer et al, 1995). We grew these antisense PHYA plants (line Ap9) and WT cv Désirée plants in the same conditions as before and looked at the StGA20ox1 transcript levels in these plants during the first couple of hours after lights on.…”

“…These antisense lines are deficient in PHYB1, however they may also have reduced levels of PHYB2 and therefore are referred to as antisense PHYB lines. The antisense PHYA transgenic lines were produced as described in Heyer et al (1995). Plants were derived from in vitro grown plants that had been planted out into soil and then subsequently propagated through stem cuttings.…”

Photoreceptor Biotechnology

“…Additional copies of the potato PHYA and Arabidopsis PHYB genes have been introduced into potato under the control of the 35S promoter (Heyer et al, 1995, Thiele et al, 1999. Overexpression of PHYA leads to dwarfing and a reduced response to R:FR (Heyer et al, 1995).…”