High impact information on PHYB

• Functional interaction of phytochrome B and cryptochrome 2 [1].
• Here we show that full-length photoactive phytochrome B binds PIF3 in vitro only upon light-induced conversion to its active form, and that photoconversion back to its inactive form causes dissociation from PIF3 [2].
• We conclude that photosensory signalling by phytochrome B involves light-induced, conformer-specific recognition of the putative transcriptional regulator PIF3, providing a potential mechanism for direct photoregulation of gene expression [2].
• Interaction of the response regulator ARR4 with phytochrome B in modulating red light signaling [3].
• The Arabidopsis thaliana response regulator 4, expressed in response to phytochrome B action, specifically interacts with the extreme amino-terminus of the photoreceptor [3].

Biological context of PHYB

• It was concluded that the pef1 mutant is defective in both PHYA- and PHYB-mediated signaling pathways, and may represent a lesion in an early step of the phytochrome signal transduction pathway [4].
• One such mutant, pef1, was selectively insensitive to both red and far-red light in the inhibition of hypocotyl elongation response; a classic phytochrome phenotype mediated by both PHYA and PHYB [4].
• To determine whether differential temporal or spatial expression patterns of the PHYA and PHYB genes contribute to this phenomenon the expression of PHYA-GUS and PHYB-GUS reporter genes has been examined in transgenic Arabidopsis [5].
• Later in the life cycle of the plant, PHYB and GAs have opposite effects on flowering [6].
• Based on Southern analyses of five black cottonwood genotypes representing three photoperiodic ecotypes, substantial polymorphism was detected for at least one of the PHYB loci but not for the PHYA locus [7].

Anatomical context of PHYB

• Phytochrome B (phyB) acts as a photoreceptor for this response [8].
• The gradual swelling of protoplasts that prevails under background red light is shown to be a phytochrome-mediated response in which phytochrome A contributes more than phytochrome B [9].

Associations of PHYB with chemical compounds

• HYPERSENSITIVE TO RED AND BLUE 1, a ZZ-type zinc finger protein, regulates phytochrome B-mediated red and cryptochrome-mediated blue light responses [10].
• Expression of an ABA biosynthesis gene, AtNCED6, and the inactivation gene, CYP707A2, was regulated in a photoreversible manner, suggesting a key role for the genes in PHYB-mediated regulation of ABA metabolism [11].
• Overexpression of Arabidopsis phytochrome B inhibits phytochrome A function in the presence of sucrose [12].
• Mutations causing defects in the biosynthesis and response to gibberellins, abscisic acid and phytochrome B do not inhibit vernalization in Arabidopsis fca-1 [13].
• We genetically dissected one mechanism that integrates hormone signals into the clock, and showed that the hormone-activated ARABIDOPSIS RESPONSE REGULATOR 4 and the photoreceptor phytochrome B are elements in the input of the cytokinin signal to circadian phase [14].

Physical interactions of PHYB

• Furthermore, the ELF3 protein interacts with PHYB in the yeast two-hybrid assay and in vitro [15].
• Using MALDI-TOF MS analysis, 7 of these candidates were predicted to be putative phytochrome A-interacting proteins and the remaining ones to be phytochrome B-interacting proteins [16].
• The response regulator 4 stabilizes the active Pfr form of phytochrome B in yeast and in planta, thus elevates the level of the active photoreceptor in vivo [3].

Regulatory relationships of PHYB

• Phytochrome B in the mesophyll delays flowering by suppressing FLOWERING LOCUS T expression in Arabidopsis vascular bundles [8].
• PHYTOCHROME B (phyB) controls period length in red light as well as the phase of the clock in white light. phyB interacts with ARABIDOPSIS RESPONSE REGULATOR4 (ARR4) in a light-dependent manner [17].
• Phytochrome A negatively or positively regulates phytochrome B signaling, depending on light conditions [18].
• Recent work indicates that ELF3 encodes a novel nuclear protein that is expressed rhythmically and interacts with phytochrome B. How ELF3 mediates the circadian gating of light responses and regulates light input to the clock is the subject of discussion [19].

Other interactions of PHYB

• PIL5 preferentially interacts with the Pfr forms of Phytochrome A (PhyA) and Phytochrome B (PhyB) [20].
• Hence, the PHYB, PHYD, and PHYE genes differ in expression pattern but these patterns overlap and interaction of these receptor forms within individual cells is possible [21].
• We demonstrate that PIF3 is polyubiquitinated rapidly and subsequently degraded in PHYA and PHYB-mediated light signaling [22].
• Interaction with PHYB was unaffected by mutation of any ZTL domain [23].
• Since phyB did not change the GA responsiveness of the LFY promoter and suppressed the lack of flowering of severe GA-deficient mutants under short days, we propose that PHYB modulates flowering time at least partially through a GA-independent pathway [6].

Analytical, diagnostic and therapeutic context of PHYB

• Fragments of these two PHYB were cloned following amplification by the polymerase chain reaction of a portion of their relatively well conserved 5' coding regions [24].

References