Blue-light mediated accumulation of nuclear-encoded transcripts coding for proteins of the thylakoid membrane is absent in the phytochrome-deficient aurea mutant of tomato

Abstract

Polyclonal antibodies against pea phytochrome detect 2 protein bands (about 116 and 120 kDa) on blots of crude protein extracts and protein of microsomal preparations of dark-grown tomato seedlings. Both protein bands are undetectable in Western blots of the aurea mutant extracts. Neither protein band is detectable after isogenic wild-type seedlings are illuminated with 3 h of red light, either in the crude extract or in the membrane fraction of the irradiated seedlings; this result is consistent with the hypothesis that both bands are phytochrome. When dark-grown wild-type seedlings are illuminated with 3 h of red light or blue light against a red light background, the transcript levels for chlorophyll a/b-binding proteins of photosystem I and II, plastocyanin, and the subunit II of photosystem I increase. In all cases, the same fluence rate of blue light is much more effective than red light alone, a result that indicates the involvement of a blue/UV-A light photoreceptor in addition to the involvement of the far-red-absorbing form of phytochrome, Pfr. The aurea mutant responds neither to red light nor to blue light. Thus, no Pfr-independent induction of the four transcripts by a blue/UV-A light photoreceptor can be measured in the aurea mutant.

Fluence and Wavelength Requirements for Arabidopsis CAB Gene Induction by Different Phytochromes

“…What is the receptor for blue-light induction of C A B expression? These studies have concluded that blue-light induction of C A B expression is regulated by the blue/UV-A photoreceptor system (Marrs and Kaufman, 1989;Oelmiiller et al, 1989;Wehmeyer et al, 1990;Gao and Kaufman, 1994) or that there is a co-action between the blue/UV-A receptor and phytochrome (Oelmüller et al, 1989). In this report we demonstrated that PhyA, PhyB, and PhyX also contribute to the blue-light regulation of C A B expression in etiolated seedlings of Arabidopsis.…”

Altered Phytochrome Regulation of Greening in an aurea Mutant of Tomato

“…The low level of protochlorophyllide in dark-grown au seedlings may result in part from a paucity of (pro)thylakoid membranes, and this can be checked with other plastid marker proteins and ultrastructural studies of the cotyledons of etiolated seedlings. The au etioplasts cannot be drastically defective, because greening was normal under low light (16). One might speculate that the mutant is defective in some aspects of the signal (3,9,15) postulated to coordinate plastid and nuclear gene expression.…”

“…Fbark-grown au seedlings contain less than 5% of the wildtype level of phytochrome, as shown by spectrophotometric and immunochemical methods (16,17). The phytochrome deficiency in au probably results from instability of the apoprotein.…”

“…Blue light promotes accumulation of several nuclear-encoded mRNAs encoding plastid proteins in wild-type seedlings, but is inactive in au seedlings (16 (4). The VLF threshold is near the theoretical limit of sensitivity (a few molecules of Pfr per cell), so that a significant reduction in phytochrome concentration should cause the VLF to vanish.…”

Photocontrol of the Accumulation of Plastid Polypeptides during Greening of Tomato Cotyledons

“…Light regulates several aspects of this greening process. In particular, continuous light is required for photoreduction of Pchlide, and a pulse of light acts through phytochrome to increase the levels of nuclear mRNAs encoding chloroplast proteins (1,9,16,18,20,21,23,24,29,30). Blue light receptors have also been implicated in the control of plastid (5) and nuclear-encoded mRNAs (20,30).…”