FUNCTIONAL-ANALYSIS OF YEAST-DERIVED PHYTOCHROME-A AND PHYTOCHROME-B PHYCOCYANOBILIN ADDUCTS

Investigations of phytochrome mutants of Arabidopsis suggested that th e expression of chalcone synthase (chs) and anthocyanin accumulation i s predominantly controlled by phytochrome A. To test the functionality of phytochrome A and B at the molecular level recombinant, yeast-deri ved phytochrome-phycocyanobilin adducts (phyA, phyB*) and oat phytoch rome A (phyA) were microinjected into etiolated aurea tomato seedlings . Subsequent to microinjection anthocyanin and chlorophyll accumulatio n was monitored as well as beta-glucuronidase (GUS) expression mediate d by light-regulated promoters (chs, chlorophyll a/b binding protein ( lhcb1] and ferredoxin NADP+ oxidoreductase (fnr)]. Microinjection of p hyA under white light conditions caused anthocyanin and chlorophyll a ccumulation and mediated chs-GUS, lhcb1-GUS and fnr-GUS expression. Mi croinjection of phyB under identical conditions induced chlorophyll a ccumulation and mediated lhcb1-GUS and fnr-GUS expression but neither anthocyanin accumulation nor chs-GUS expression were observed. The cha racterization of Arabidopsis phytochrome mutants and the microinjectio n experiments suggested that phyB cannot induce the accumulation of ju venile anthocyanin. Microinjections under far-red light conditions dem onstrated that phyA can act independently of other photoreceptors. By contrast, phyB injections under red light conditions indicated that p hyB needs interactions with other photoreceptors to mediate a rapid a nd efficient de-etiolation signal.