Regulation of transcript levels of a potato gibberellin 20-oxidase gene bylight and phytochrome B

Up to three gibberellin (GA) 20-oxidase genes have now been cloned from sev eral species including Arabidopsis, bean (Phaseolus vulgaris), and potato ( Solanum tuberosum). In each case the GA 20-oxidase genes exhibit different patterns of tissue expression We have performed extensive northern analysis on one of the potato GA 20-oxidase genes (StGA20ox1), which is the only on e that shows significant transcript levels in leaves. We show that levels o f StGA20ox1 transcript are elevated in transgenic antisense plants that hav e reduced levels of phytochrome B (PHYB) compared with wild-type plants, im plicating PHYB in the control of GA biosynthesis. We show that StGA20ox1 tr anscript levels vary in leaves of different age throughout the plant and cy cle throughout the day, furthermore they are up-regulated by light and down -regulated in the dark. The degree of the response to the light-on signal i s similar in potato plants deficient in phytochrome A or PHYB and wild-type plants. The induction of StGA20ox1 by blue light raises the possibility th at a blue light receptor may be involved in the control of this gene by lig ht.