Sustained but Not Transient Phytochrome A Signaling Targets a Region of an Lhcb1*2 Promoter Not Necessary for Phytochrome B Action (original) (raw)
Related papers
Photochemistry and Photobiology, 2000
The plant receptor phytochrome A (phyA) mediates responses like hypocotyl growth inhibition and cotyledon unfolding that require continuous far-red (FR) light for maximum expression (high-irradiance responses, HIR), and responses like seed germination that can be induced by a single pulse of FR (very-low-fluence responses, VLFR). It is not known whether this duality results from either phyA interaction with different end-point processes or from the intrinsic properties of phyA activity. Etiolated seedlings of Arabidopsis thaliana were exposed to pulses of FR (3 min) separated by dark intervals of different duration. Hypocotyl-growth inhibition and cotyledon unfolding showed two phases. The first phase (VLFR) between 0.17 and 0.5 pulses•h Ϫ1 , a plateau between 0.5 and 2 pulses•h Ϫ1 and a second phase (HIR) at higher frequencies. Reciprocity between fluence rate and duration of FR was observed within phases, not between phases. The fluence rate for half the maximum effect was 0.1 and 3 mol•m Ϫ2 •s Ϫ1 for hourly pulses of FR (VLFR) and continuous FR (HIR), respectively. Overexpression of phytochrome B caused dominant negative suppression under continuous but not under hourly FR. We conclude that phyA is intrinsically able to initiate two discrete photoresponses even when a single end-point process is considered.
The Plant Journal, 1997
et al., 1995a; Malhotra et al.,1995), and overexpression of USA CRY1 protein in transgenic plants conferred a blue-light hypersensitive phenotype (Lin et al.,1995b), consistent with its role as photoreceptor. Blue-light-dependent phenotypes Summary shown to be under the control of CRY1 include inhibition Blue-light responses in higher plants are mediated by of hypocotyl elongation and anthocyanin production in specific photoreceptors, which are thought to be flavoseedlings (Ahmad et al., 1995; Jackson and Jenkins, 1995; proteins; one such flavin-type blue-light receptor, CRY1 Koornneef et al., 1980). In spite of its striking homology to (for cryptochrome), which mediates inhibition of hypocotyl the DNA photolyases, CRY1 shows no demonstrable DNA elongation and anthocyanin biosynthesis, has recently binding or photoreactivating activity (Lin et al., 1995a; been characterized. Prompted by classical photobiological Malhotra et al., 1995). The structure of CRY1 suggests a studies suggesting possible co-action of the red/far-red mechanism of action involving electron transfer; the reacabsorbing photoreceptor phytochrome with blue-light tion partners and downstream transduction apparatus photoreceptors in certain plant species, the role of phytoremain to be identified. chrome in CRY1 action in Arabidopsis was investigated. A recurring theme in plant blue-light research has been The activity of the CRY1 photoreceptor can be substantially an involvement of the red/far-red-absorbing photoreceptor altered by manipulating the levels of active phytochrome phytochrome in physiological responses to blue-light treat-(Pfr) with red or far-red light pulses subsequent to bluements. Experiments in a number of monocot and dicot light treatments. Furthermore, analysis of severely phytoplant species have shown that blue-light responses such chrome-deficient mutants showed that CRY1-mediated as inhibition of hypocotyl elongation or anthocyanin accublue-light responses were considerably reduced, even mulation can be partially reversed if the blue-light pulses though Western blots confirmed that levels of CRY1 photoare followed by, or given in the presence of, saturating receptor are unaffected in these phytochrome-deficient pulses of far-red light (Casal, 1994; Gaba et al., 1984; mutant backgrounds. It was concluded that CRY1-medi-Mancinelli et al., 1991; Mohr, 1994). Such far-red reversiated inhibition of hypocotyl elongation and anthocyanin bility had been taken as evidence that phytochrome, or the production requires active phytochrome for full expresphytochrome signal transduction pathway, was somehow sion, and that this requirement can be supplied by low implicated in blue-light responses. However, interpretation levels of either phyA or phyB. of these studies has been complicated by the fact that the phytochrome photoreceptor itself directly absorbs blue light. It is therefore difficult to unequivocally distinguish
Phytochromes B, D, and E act redundantly to control multiple physiological responses in Arabidopsis
Plant …, 2003
Phytochrome-mediated perception of the ratio of red to far-red wavelengths in the ambient light environment is fundamental to plant growth and development. Such monitoring enables plants to detect neighboring vegetation and initiate avoidance responses, thus conferring considerable selective advantage. The shade avoidance syndrome in plants is characterized by elongation growth and early flowering, responses that are fully induced by end-of-day far-red light treatments. Elucidating the roles of individual phytochromes in mediating responses to red to far-red has however always been confounded by synergistic and mutually antagonistic coactions between family members. The creation of triple and quadruple mutants in Arabidopsis, deficient in multiple phytochromes, has revealed functional redundancy between phyB, D, and E in controlling flowering time, leaf development, and regulation of the homeobox gene, ATHB-2. In addition, mutant analysis suggests a possible novel role for phyC in suppressing ATHB-2 transcription in the light. fax 44 -0116 -252-3330.
Phytochrome-mediated light signaling in plants: emerging trends
Physiology and Molecular Biology of Plants, 2008
Like other living organisms, plant development is also determined genetically but is modulated dramatically by diverse environmental signals. Among these, light plays a profound role and regulates virtually all aspects of plant life cycle, starting from seed germination through to senescence. Plants perceive changes in the ambient light environment by distinct sensory photoreceptors. The conventional photoreceptors include three major classes in plants, viz. the red/far-red (R/FR) light-sensing phytochromes and UV-A/blue light-perceiving cryptochromes and phototropins (Jiao et al., 2007). However, the molecular nature of the UV-B (280-320 nm) photoreceptor(s) is still elusive. Recently, additional blue light photoreceptors called ZEITLUPE have been characterized (
Phytochrome Regulation and Differential Expression of
2000
Despite extensive studies on the roles of phytochrome in photostimulated seed germination, the mechanisms downstream of the photoreceptor that promote germination are largely unknown. Previous studies have indicated that light-induced germination of Arabidopsis seeds is mediated by the hormone gibberellin (GA). Using RNA gel blot analyses, we studied the regulation of two Arabidopsis genes, GA4 and GA4H (for GA4 homolog), both of which encode GA 3  -hydroxylases that catalyze the final biosynthetic step to produce bioactive GAs. The newly isolated GA4H gene was expressed predominantly during seed germination. We show that expression of both GA4 and GA4H genes in imbibed seeds was induced within 1 hr after a brief red (R) light treatment. In the phytochrome B-deficient phyB-1 mutant, GA4H expression was not induced by R light, but GA4 expression still was, indicating that R light-induced GA4 and GA4H expression is mediated by different phytochromes. In contrast to the GA4 gene, the GA4H gene was not regulated by the feedback inhibition mechanism in germinating seeds. Our data demonstrate that expression of GA 3  -hydroxylase genes is elevated by R light, which may result in an increase in biosynthesis of active GAs to promote seed germination. Furthermore, our results suggest that each GA 3  -hydroxylase gene plays a unique physiological role during light-induced seed germination.
Overexpression of homologous phytochrome genes in tomato: exploring the limits in photoperception
Journal of Experimental Botany, 2007
Transgenic tomato [Lycopersicon esculentum (=Solanum lycopersicum)] lines overexpressing tomato PHYA, PHYB1, or PHYB2, under control of the constitutive double-35S promoter from cauliflower mosaic virus (CaMV) have been generated to test the level of saturation in individual phytochrome-signalling pathways in tomato. Western blot analysis confirmed the elevated phytochrome protein levels in dark-grown seedlings of the respective PHY overexpressing (PHYOE) lines. Exposure to 4 h of red light resulted in a decrease in phytochrome A protein level in the PHYAOE lines, indicating that the chromophore availability is not limiting for assembly into holoprotein and that the excess of phytochrome A protein is also targeted for light-regulated destruction. The elongation and anthocyanin accumulation responses of plants grown under white light, red light, far-red light, and end-of-day far-red light were used for characterization of selected PHYOE lines. In addition, the anthocyanin accumulation response to different fluence rates of red light of 4-d-old dark-grown seedlings was studied. The elevated levels of phyA in the PHYAOE lines had little effect on seedling and adult plant phenotype. Both PHYAOE in the phyA mutant background and PHYB2OE in the double-mutant background rescued the mutant phenotype, proving that expression of the transgene results in biologically active phytochrome. The PHYB1OE lines showed mild effects on the inhibition of stem elongation and anthocyanin accumulation and little or no effect on the red light high irradiance response. By contrast, the PHYB2OE lines showed a strong inhibition of elongation, enhancement of anthocyanin accumulation, and a strong amplification of the red light high irradiance response.
PLANT PHYSIOLOGY, 2002
Phytochrome (phy) A mediates two distinct photobiological responses in plants: the very-low-fluence response (VLFR), which can be saturated by short pulses of very-low-fluence light, and the high-irradiance response (HIR), which requires prolonged irradiation with higher fluences of far-red light (FR). To investigate whether the VLFR and HIR involve different domains within the phyA molecule, transgenic tobacco (Nicotiana tabacum cv Xanthi) and Arabidopsis seedlings expressing full-length (FL) and various deletion mutants of oat (Avena sativa) phyA were examined for their light sensitivity. Although most mutants were either partially active or inactive, a strong differential effect was observed for the ⌬6-12 phyA mutant missing the serine-rich domain between amino acids 6 and 12. ⌬6-12 phyA was as active as FL phyA for the VLFR of hypocotyl growth and cotyledon unfolding in Arabidopsis, and was hyperactive in the VLFR of hypocotyl growth and cotyledon unfolding in tobacco, and the VLFR blocking subsequent greening under white light in Arabidopsis. In contrast, ⌬6-12 phyA showed a dominant-negative suppression of HIR in both species. In hypocotyl cells of Arabidopsis irradiated with FR phyA:green fluorescent protein (GFP) and ⌬6-12 phyA:GFP fusions localized to the nucleus and coalesced into foci. The proportion of nuclei with abundant foci was enhanced by continuous compared with hourly FR provided at equal total fluence in FL phyA:GFP, and by ⌬6-12 phyA mutation under hourly FR. We propose that the N-terminal serine-rich domain of phyA is involved in channeling downstream signaling via the VLFR or HIR pathways in different cellular contexts. fax 5411-45148730.
Phytochrome Control of the Arabidopsis Transcriptome Anticipates Seedling Exposure to Light
The Plant Cell …, 2005
María Agustina Mazzella a, 1, María Verónica Arana b, 1, Roberto J. Staneloni c, Susana Perelman b, María J. Rodriguez Batiller c, Jorge Muschietti a, Pablo D. Cerdán d, Kunhua Chen d, Rodolfo A. Sánchez b, Tong Zhu e, Joanne Chory d and Jorge J. Casal b, 2
Overexpression of Phytochrome B Induces a Short Hypocotyl Phenotype in Transgenic Arabidopsis
The Plant Cell, 1991
The photoreceptor phytochrome is encoded by a small multigene family in higher plants. phyA encodes the wellcharacterized etiolated-tissue phytochrome. The product of the phyB gene, which has properties resembling those of "green tissue" phytochrome, is as yet poorly characterized. We have developed a phytochrome B overexpression system for analysis of the structure and function of this protein. Using newly generated polyclonal and monoclonal antibodies that are selective for phytochrome B, we have demonstrated high levels of expression of full-length rice and Arabidopsis phytochrome B under the control of the cauliflower mosaic virus 35s promoter in transgenic Arabidopsis. The overexpressed phytochrome is spectrally active, undergoes red/far-red-light-dependent conformational changes, is synthesized in its inactive red light-absorbing form, and is stable in the light. Overexpression of phytochrome 6 is tightly correlated with a short hypocotyl phenotype in transgenic seedlings. This phenotype is strictly light dependent, thus providing direct evidence that phytochrome B is a biologically functional photoreceptor. Based on similarities to phenotypes obtained by overexpression of phytochrome A, it appears that phytochromes A and B can control similar responses in the plant.
Arabidopsis Contains at Least Four Independent Blue-Light-Activated Signal Transduction Pathways
PLANT PHYSIOLOGY, 1999
sis. The stomatal responses of light-grown mutant plants (cry1, cry2, nph1, nph3, nph4, cry1cry2, and nph1cry1) did not differ significantly from those of their wild-type counterparts. Second positive phototropic responses of etiolated mutant seedlings, cry1, cry2, cry1cry2, and npq1-2, were also similar to those of their wild-type counterparts. Although npq1 and single and double cry1cry2 mutants showed somewhat reduced amplitude for first positive phototropism, threshold, peak, and saturation fluence values for first positive phototropic responses of etiolated seedlings did not differ from those of wild-type seedlings. Similar to the cry1cry2 double mutants and to npq1-2, a phyAphyB mutant showed reduced curvature but no change in the position or shape of the fluenceresponse curve. By contrast, the phototropism mutant nph1-5 failed to show phototropic curvature under any of the irradiation conditions used in the present study. We conclude that the chromoproteins cry1, cry2, nph1, and the blue-light photoreceptor for the stomatal response are genetically separable. Moreover, these photoreceptors appear to activate separate signal transduction pathways.