Novel phytochrome sequences in Arabidopsis thaliana: structure, evolution, and differential expression of a plant regulatory photoreceptor family.

Abstract

Phytochrome is a plant regulatory photoreceptor that mediates red light effects on a wide variety of physiological and molecular responses. DNA blot analysis indicates that the Arabidopsis thaliana genome contains four to five phytochrome-related gene sequences. We have isolated and sequenced cDNA clones corresponding to three of these genes and have deduced the amino acid sequence of the full-length polypeptide encoded in each case. One of these proteins ipbyA) shows 65-80% amino acid sequence identity with the major, etiolated-tissue phytochrome apoproteins described previously in other plant species. The other two polypeptides {pbyB and pbyC) are unique in that they have low sequence identity (-50%) with each other, with pbyA, and with all previously described phytochromes. The pbyA, pbyB, and pbyC proteins are of similar molecular mass, have related hydropathic profiles, and contain a conserved chromophore attachment region. However, the sequence comparison data indicate that the three pby genes diverged early in plant evolution, well before the divergence of the two major groups of angiosperms, the monocots and dicots. The steady-state level of the pbyA transcript is high in dark-grown A. tbaliana seedlings and is down-regulated by light. In contrast, the pbyB and pbyC transcripts are present at lower levels and are not strongly light-regulated. These findings indicate that the red/far red light-responsive phytochrome photoreceptor system in A. tbaliana, and perhaps in all higher plants, consists of a family of chromoproteins that are heterogeneous in structure and regulation.

Photo and hormonal control of meristem identity in the Arabidopsis flower mutants apetala2 and apetala1.

“…To explore this hypothesis, we used a genetic approach to test whether phytochrome activity is required for SD axillary flower formation. There are at least five phytochrome genes in Arabidopsis (PHYA to PHYE; Sharrock and Quail, 1989;Clack et al, 1994). The activities of all five genes are strongly suppressed by the hy7 mutation that blocks phytochrome chromophore biosynthesis (Parks and Quail, 1991).…”

Light-Induced Nuclear Translocation of Endogenous Pea Phytochrome A Visualized by Immunocytochemical Procedures

“…Phytochromes are soluble chromoproteins that convert photoreversibly between two spectrally distinct forms when sequentially absorbing red (R) and far-red (FR) light, and this interconversion occurs immediately both in vivo and in vitro (Butler et al, 1959). Phytochromes are encoded by a small gene family (phytochrome genes PHYA to PHYE in Arabidopsis; Sharrock and Quail, 1989;Clack et al, 1994). Studies with mutants deficient in specific phytochromes have shown that phytochrome A (PhyA) and phytochrome B (PhyB) have distinct action spectra for the photoinduction of seed germination (Shinomura et al, 1996) and distinct fluence and wavelength requirements for expression of the chlorophyll a / b binding protein gene ( CAB ) (Hamazato et al, 1997).…”

Lysine 206 inArabidopsisphytochrome A is the major site for ubiquitin-dependent protein degradation

“…Active Pfr form can be converted back to the inactive Pr form by absorption of specific far-red light (9,10). The model plant, Arabidopsis thaliana, contains five genes (PHYA to PHYE) that encode phytochrome apoproteins (11,12). Phytochromes are classified as light labile phytochrome A (phyA) and light stable phytochromes B E (phyB-phyE) (13).…”