Transcriptomic, proteomic and metabolomic analysis of UV-B signaling in maize

<p>Abstract</p> <p>Background</p> <p>Under normal solar fluence, UV-B damages macromolecules, but it also elicits physiological acclimation and developmental changes in plants. Excess UV-B decreases crop yield. Using a treatment twice solar fluence, we focus on discovering signals produced in UV-B-irradiated maize leaves that translate to systemic changes in shielded leaves and immature ears.</p> <p>Results</p> <p>Using transcriptome and proteomic profiling, we tracked the kinetics of transcript and protein alterations in exposed and shielded organs over 6 h. In parallel, metabolic profiling identified candidate signaling molecules based on rapid increase in irradiated leaves and increased levels in shielded organs; pathways associated with the synthesis, sequestration, or degradation of some of these potential signal molecules were UV-B-responsive. Exposure of just the top leaf substantially alters the transcriptomes of both irradiated and shielded organs, with greater changes as additional leaves are irradiated. Some phenylpropanoid pathway genes are expressed only in irradiated leaves, reflected in accumulation of pathway sunscreen molecules. Most protein changes detected occur quickly: approximately 92% of the proteins in leaves and 73% in immature ears changed after 4 h UV-B were altered by a 1 h UV-B treatment.</p> <p>Conclusions</p> <p>There were significant transcriptome, proteomic, and metabolomic changes under all conditions studied in both shielded and irradiated organs. A dramatic decrease in transcript diversity in irradiated and shielded leaves occurs between 0 h and 1 h, demonstrating the susceptibility of plants to short term UV-B spikes as during ozone depletion. Immature maize ears are highly responsive to canopy leaf exposure to UV-B.</p

Cross-talk between high light stress and plant defence to the two-spotted spider mite in Arabidopsis thaliana

Little is known about how plants deal with arthropod herbivores under the fluctuating light intensity and spectra which occur in natural environments. Moreover, the role of simultaneous stress such as excess light (EL) in the regulation of plant responses to herbivores is poorly characterized. In the current study, we focused on a mite-herbivore, specifically, the two-spotted spider mite (TSSM), which is one of the major agricultural pests worldwide. Our results showed that TSSM-induced leaf damage (visualized by trypan blue staining) and oviposition rate (measured as daily female fecundity) decreased after EL pre-treatment in wild-type Arabidopsis plants, but the observed responses were not wavelength specific. Thus, we established that EL pre-treatment reduced Arabidopsis susceptibility to TSSM infestation. Due to the fact that a portion of EL energy is dissipated by plants as heat in the mechanism known as non-photochemical quenching (NPQ) of chlorophyll fluorescence, we tested an Arabidopsis npq4-1 mutant impaired in NPQ. We showed that npq4-1 plants are significantly less susceptible to TSSM feeding activity, and this result was not dependent on light pre-treatment. Therefore, our findings strongly support the role of light in plant defence against TSSM, pointing to a key role for a photo-protective mechanism such as NPQ in this regulation. We hypothesize that plants impaired in NPQ are constantly primed to mite attack, as this seems to be a universal evolutionarily conserved mechanism for herbivores

GmFT2a, a Soybean Homolog of FLOWERING LOCUS T, Is Involved in Flowering Transition and Maintenance

BACKGROUND: Flowering reversion can be induced in soybean (Glycine max L. Merr.), a typical short-day (SD) dicot, by switching from SD to long-day (LD) photoperiods. This process may involve florigen, putatively encoded by FLOWERING LOCUS T (FT) in Arabidopsis thaliana. However, little is known about the potential function of soybean FT homologs in flowering reversion. METHODS: A photoperiod-responsive FT homologue GmFT (renamed as GmFT2a hereafter) was cloned from the photoperiod-sensitive cultivar Zigongdongdou. GmFT2a gene expression under different photoperiods was analyzed by real-time quantitative PCR. In situ hybridization showed direct evidence for its expression during flowering-related processes. GmFT2a was shown to promote flowering using transgenic studies in Arabidopsis and soybean. The effects of photoperiod and temperature on GmFT2a expression were also analyzed in two cultivars with different photoperiod-sensitivities. RESULTS: GmFT2a expression is regulated by photoperiod. Analyses of GmFT2a transcripts revealed a strong correlation between GmFT2a expression and flowering maintenance. GmFT2a transcripts were observed continuously within the vascular tissue up to the shoot apex during flowering. By contrast, transcripts decreased to undetectable levels during flowering reversion. In grafting experiments, the early-flowering, photoperiod-insensitive stock Heihe27 promotes the appearance of GmFT2a transcripts in the shoot apex of scion Zigongdongdou under noninductive LD conditions. The photothermal effects of GmFT2a expression diversity in cultivars with different photoperiod-sensitivities and a hypothesis is proposed. CONCLUSION: GmFT2a expression is associated with flowering induction and maintenance. Therefore, GmFT2a is a potential target gene for soybean breeding, with the aim of increasing geographic adaptation of this crop

The arabidopsis DNA polymerase δ has a role in the deposition of transcriptionally active epigenetic marks, development and flowering

DNA replication is a key process in living organisms. DNA polymerase α (Polα) initiates strand synthesis, which is performed by Polε and Polδ in leading and lagging strands, respectively. Whereas loss of DNA polymerase activity is incompatible with life, viable mutants of Polα and Polε were isolated, allowing the identification of their functions beyond DNA replication. In contrast, no viable mutants in the Polδ polymerase-domain were reported in multicellular organisms. Here we identify such a mutant which is also thermosensitive. Mutant plants were unable to complete development at 28°C, looked normal at 18°C, but displayed increased expression of DNA replication-stress marker genes, homologous recombination and lysine 4 histone 3 trimethylation at the SEPALLATA3 (SEP3) locus at 24°C, which correlated with ectopic expression of SEP3. Surprisingly, high expression of SEP3 in vascular tissue promoted FLOWERING LOCUS T (FT) expression, forming a positive feedback loop with SEP3 and leading to early flowering and curly leaves phenotypes. These results strongly suggest that the DNA polymerase δ is required for the proper establishment of transcriptionally active epigenetic marks and that its failure might affect development by affecting the epigenetic control of master genes.Fil: Iglesias, Francisco Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquimicas de Buenos Aires; Argentina. Fundación Instituto Leloir; ArgentinaFil: Bruera, Natalia Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquimicas de Buenos Aires; Argentina. Fundación Instituto Leloir; ArgentinaFil: Dergan Dylon, Leonardo Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquimicas de Buenos Aires; Argentina. Fundación Instituto Leloir; ArgentinaFil: Marino, Cristina Ester. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquimicas de Buenos Aires; Argentina. Fundación Instituto Leloir; ArgentinaFil: Lorenzi, Hernán. J. Craig Venter Institute; Estados UnidosFil: Mateos, Julieta Lisa. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquimicas de Buenos Aires; Argentina. Fundación Instituto Leloir; Argentina. Max Planck Institute for Plant Breeding Research; AlemaniaFil: Turck, Franziska. Max Planck Institute for Plant Breeding Research; AlemaniaFil: Coupland, George. Max Planck Institute for Plant Breeding Research; AlemaniaFil: Cerdan, Pablo Diego. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquimicas de Buenos Aires; Argentina. Fundación Instituto Leloir; Argentina. Universidad de Buenos Aires. Departamento de Ciencias Exactas; Argentin

Latent tuberculosis infection, tuberculin skin test and vitamin D status in contacts of tuberculosis patients: a cross-sectional and case-control study

<p>Abstract</p> <p>Background</p> <p>Deficient serum vitamin D levels have been associated with incidence of tuberculosis (TB), and latent tuberculosis infection (LTBI). However, to our knowledge, no studies on vitamin D status and tuberculin skin test (TST) conversion have been published to date. The aim of this study was to estimate the associations of serum 25-hydroxyvitamin D₃(25[OH]D) status with LTBI prevalence and TST conversion in contacts of active TB in Castellon (Spain).</p> <p>Methods</p> <p>The study was designed in two phases: cross-sectional and case-control. From November 2009 to October 2010, contacts of 42 TB patients (36 pulmonary, and 6 extra-pulmonary) were studied in order to screen for TB. LTBI and TST conversion cases were defined following TST, clinical, analytic and radiographic examinations. Serum 25(OH)D levels were measured by electrochemiluminescence immunoassay (ECLIA) on a COBAS^®410 ROCHE^®analyzer. Logistic regression models were used in the statistical analysis.</p> <p>Results</p> <p>The study comprised 202 people with a participation rate of 60.1%. Only 20.3% of the participants had a sufficient serum 25(OH)D (≥ 30 ng/ml) level. In the cross-sectional phase, 50 participants had LTBI and no association between LTBI status and serum 25(OH)D was found. After 2 months, 11 out of 93 negative LTBI participants, without primary prophylaxis, presented TST conversion with initial serum 25(OH)D levels: a:19.4% (7/36): < 20 ng/ml, b:12.5% (4/32):20-29 ng/ml, and c:0%(0/25) ≥ 30 ng/ml. A sufficient serum 25(OH)D level was a protector against TST conversion a: Odds Ratio (OR) = 1.00; b: OR = 0.49 (95% confidence interval (CI) 0.07-2.66); and c: OR = 0.10 (95% CI 0.00-0.76), trends p = 0.019, adjusted for high exposure and sputum acid-fast bacilli positive index cases. The mean of serum level 25(OH)D in TST conversion cases was lower than controls,17.5 ± 5.6 ng/ml versus 25.9 ± 13.7 ng/ml (p = 0.041).</p> <p>Conclusions</p> <p>The results suggest that sufficient serum 25(OH)D levels protect against TST conversion.</p

Using Light to Improve Commercial Value

The plasticity of plant morphology has evolved to maximize reproductive fitness in response to prevailing environmental conditions. Leaf architecture elaborates to maximize light harvesting, while the transition to flowering can either be accelerated or delayed to improve an individual's fitness. One of the most important environmental signals is light, with plants using light for both photosynthesis and as an environmental signal. Plants perceive different wavelengths of light using distinct photoreceptors. Recent advances in LED technology now enable light quality to be manipulated at a commercial scale, and as such opportunities now exist to take advantage of plants' developmental plasticity to enhance crop yield and quality through precise manipulation of a crops' lighting regime. This review will discuss how plants perceive and respond to light, and consider how these specific signaling pathways can be manipulated to improve crop yield and quality

Pathogen and Circadian Controlled 1 (PCC1) Protein Is Anchored to the Plasma Membrane and Interacts with Subunit 5 of COP9 Signalosome in Arabidopsis

The Pathogen and Circadian Controlled 1 (PCC1) gene, previously identified and further characterized as involved in defense to pathogens and stress-induced flowering, codes for an 81-amino acid protein with a cysteine-rich C-terminal domain. This domain is essential for homodimerization and anchoring to the plasma membrane. Transgenic plants with the ß- glucuronidase (GUS) reporter gene under the control of 1.1 kb promoter sequence of PCC1 gene display a dual pattern of expression. At early post-germination, PCC1 is expressed only in the root vasculature and in the stomata guard cells of cotyledons. During the transition from vegetative to reproductive development, PCC1 is strongly expressed in the vascular tissue of petioles and basal part of the leaf, and it further spreads to the whole limb in fully expanded leaves. This developmental pattern of expression together with the late flowering phenotype of long-day grown RNA interference (iPCC1) plants with reduced PCC1 expression pointed to a regulatory role of PCC1 in the photoperiod-dependent flowering pathway. iPCC1 plants are defective in light perception and signaling but are not impaired in the function of the core CO-FT module of the photoperiod-dependent pathway. The regulatory effect exerted by PCC1 on the transition to flowering as well as on other reported phenotypes might be explained by a mechanism involving the interaction with the subunit 5 of the COP9 signalosome (CSN).This work was funded by grants BIO2008-00839, BIO2011-27526 and CSD2007-0057 from Ministerio de Ciencia e Innovacion of Spain to J.L. A fellowship/contract of the FPU program of the Ministerio de Educacion y Ciencia (Spain) funded R.M. work. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Mir Moreno, R.; Leon Ramos, J. (2014). Pathogen and Circadian Controlled 1 (PCC1) Protein Is Anchored to the Plasma Membrane and Interacts with Subunit 5 of COP9 Signalosome in Arabidopsis. PLoS ONE. 1(9):1-14. https://doi.org/10.1371/journal.pone.0087216S11419Sauerbrunn, N., & Schlaich, N. L. (2004). PCC1 : a merging point for pathogen defence and circadian signalling in Arabidopsis. Planta, 218(4), 552-561. doi:10.1007/s00425-003-1143-zSEGARRA, S., MIR, R., MARTÍNEZ, C., & LEÓN, J. (2009). Genome-wide analyses of the transcriptomes of salicylic acid-deficient versus wild-type plants uncover Pathogen and Circadian Controlled 1 (PCC1) as a regulator of flowering time in Arabidopsis. Plant, Cell & Environment, 33(1), 11-22. doi:10.1111/j.1365-3040.2009.02045.xVenancio, T. M., & Aravind, L. (2009). CYSTM, a novel cysteine-rich transmembrane module with a role in stress tolerance across eukaryotes. Bioinformatics, 26(2), 149-152. doi:10.1093/bioinformatics/btp647Lau, O. S., & Deng, X. W. (2010). Plant hormone signaling lightens up: integrators of light and hormones. Current Opinion in Plant Biology, 13(5), 571-577. doi:10.1016/j.pbi.2010.07.001Seo, M., Nambara, E., Choi, G., & Yamaguchi, S. (2008). Interaction of light and hormone signals in germinating seeds. Plant Molecular Biology, 69(4), 463-472. doi:10.1007/s11103-008-9429-yDe Lucas, M., Davière, J.-M., Rodríguez-Falcón, M., Pontin, M., Iglesias-Pedraz, J. M., Lorrain, S., … Prat, S. (2008). A molecular framework for light and gibberellin control of cell elongation. Nature, 451(7177), 480-484. doi:10.1038/nature06520Feng, S., Martinez, C., Gusmaroli, G., Wang, Y., Zhou, J., Wang, F., … Deng, X. W. (2008). Coordinated regulation of Arabidopsis thaliana development by light and gibberellins. Nature, 451(7177), 475-479. doi:10.1038/nature06448Mutasa-Gottgens, E., & Hedden, P. (2009). Gibberellin as a factor in floral regulatory networks. Journal of Experimental Botany, 60(7), 1979-1989. doi:10.1093/jxb/erp040Bastian, R., Dawe, A., Meier, S., Ludidi, N., Bajic, V. B., & Gehring, C. (2010). Gibberellic acid and cGMP-dependent transcriptional regulation inArabidopsis thaliana. Plant Signaling & Behavior, 5(3), 224-232. doi:10.4161/psb.5.3.10718Yu, S., Galvão, V. C., Zhang, Y.-C., Horrer, D., Zhang, T.-Q., Hao, Y.-H., … Wang, J.-W. (2012). Gibberellin Regulates the Arabidopsis Floral Transition through miR156-Targeted SQUAMOSA PROMOTER BINDING–LIKE Transcription Factors. The Plant Cell, 24(8), 3320-3332. doi:10.1105/tpc.112.101014Arc, E., Galland, M., Cueff, G., Godin, B., Lounifi, I., Job, D., & Rajjou, L. (2011). Reboot the system thanks to protein post-translational modifications and proteome diversity: How quiescent seeds restart their metabolism to prepare seedling establishment. PROTEOMICS, 11(9), 1606-1618. doi:10.1002/pmic.201000641Dill, A., Thomas, S. G., Hu, J., Steber, C. M., & Sun, T. (2004). The Arabidopsis F-Box Protein SLEEPY1 Targets Gibberellin Signaling Repressors for Gibberellin-Induced Degradation. The Plant Cell, 16(6), 1392-1405. doi:10.1105/tpc.020958Wang, F., & Deng, X. W. (2011). Plant ubiquitin-proteasome pathway and its role in gibberellin signaling. Cell Research, 21(9), 1286-1294. doi:10.1038/cr.2011.118Hotton, S. K., & Callis, J. (2008). Regulation of Cullin RING Ligases. Annual Review of Plant Biology, 59(1), 467-489. doi:10.1146/annurev.arplant.58.032806.104011Cope, G. A. (2002). Role of Predicted Metalloprotease Motif of Jab1/Csn5 in Cleavage of Nedd8 from Cul1. Science, 298(5593), 608-611. doi:10.1126/science.1075901Gusmaroli, G., Figueroa, P., Serino, G., & Deng, X. W. (2007). Role of the MPN Subunits in COP9 Signalosome Assembly and Activity, and Their Regulatory Interaction with Arabidopsis Cullin3-Based E3 Ligases. The Plant Cell, 19(2), 564-581. doi:10.1105/tpc.106.047571Serino, G., & Deng, X.-W. (2003). THECOP9 SIGNALOSOME: Regulating Plant Development Through the Control of Proteolysis. Annual Review of Plant Biology, 54(1), 165-182. doi:10.1146/annurev.arplant.54.031902.134847Stratmann, J. W., & Gusmaroli, G. (2012). Many jobs for one good cop – The COP9 signalosome guards development and defense. Plant Science, 185-186, 50-64. doi:10.1016/j.plantsci.2011.10.004Lozano-Juste, J., & León, J. (2011). Nitric Oxide Regulates DELLA Content and PIF Expression to Promote Photomorphogenesis in Arabidopsis. Plant Physiology, 156(3), 1410-1423. doi:10.1104/pp.111.177741Nakagawa, T., Kurose, T., Hino, T., Tanaka, K., Kawamukai, M., Niwa, Y., … Kimura, T. (2007). Development of series of gateway binary vectors, pGWBs, for realizing efficient construction of fusion genes for plant transformation. Journal of Bioscience and Bioengineering, 104(1), 34-41. doi:10.1263/jbb.104.34Fromont-Racine, M., Rain, J.-C., & Legrain, P. (1997). Toward a functional analysis of the yeast genome through exhaustive two-hybrid screens. Nature Genetics, 16(3), 277-282. doi:10.1038/ng0797-277Belda-Palazón B, Ruiz L, Martí E, Tárraga S, Tiburcio AF, et al.. (2012) Aminopropyltransferases involved in polyamine biosynthesis localize preferentially in the nucleus of plant cells. PLoS One 7(10), e46907.Simon, R., Igeño, M. I., & Coupland, G. (1996). Activation of floral meristem identity genes in Arabidopsis. Nature, 384(6604), 59-62. doi:10.1038/384059a0Martínez, C., Pons, E., Prats, G., & León, J. (2003). Salicylic acid regulates flowering time and links defence responses and reproductive development. The Plant Journal, 37(2), 209-217. doi:10.1046/j.1365-313x.2003.01954.xKyte, J., & Doolittle, R. F. (1982). A simple method for displaying the hydropathic character of a protein. Journal of Molecular Biology, 157(1), 105-132. doi:10.1016/0022-2836(82)90515-0Marmagne, A., Rouet, M.-A., Ferro, M., Rolland, N., Alcon, C., Joyard, J., … Ephritikhine, G. (2004). Identification of New Intrinsic Proteins inArabidopsisPlasma Membrane Proteome. Molecular & Cellular Proteomics, 3(7), 675-691. doi:10.1074/mcp.m400001-mcp200Nühse, T. S., Stensballe, A., Jensen, O. N., & Peck, S. C. (2004). Phosphoproteomics of the Arabidopsis Plasma Membrane and a New Phosphorylation Site Database. The Plant Cell, 16(9), 2394-2405. doi:10.1105/tpc.104.023150Kobayashi, Y., & Weigel, D. (2007). Move on up, it’s time for change mobile signals controlling photoperiod-dependent flowering. Genes &amp; Development, 21(19), 2371-2384. doi:10.1101/gad.1589007Jaeger, K. E., & Wigge, P. A. (2007). FT Protein Acts as a Long-Range Signal in Arabidopsis. Current Biology, 17(12), 1050-1054. doi:10.1016/j.cub.2007.05.008Mathieu, J., Warthmann, N., Küttner, F., & Schmid, M. (2007). Export of FT Protein from Phloem Companion Cells Is Sufficient for Floral Induction in Arabidopsis. Current Biology, 17(12), 1055-1060. doi:10.1016/j.cub.2007.05.009Mir, R., Hernández, M. L., Abou-Mansour, E., Martínez-Rivas, J. M., Mauch, F., Métraux, J.-P., & León, J. (2013). Pathogen and Circadian Controlled 1 (PCC1) regulates polar lipid content, ABA-related responses, and pathogen defence in Arabidopsis thaliana. Journal of Experimental Botany, 64(11), 3385-3395. doi:10.1093/jxb/ert177Nordgård, O., Dahle, Ø., Andersen, T. Ø., & Gabrielsen, O. S. (2001). JAB1/CSN5 interacts with the GAL4 DNA binding domain: A note of caution about two-hybrid interactions. Biochimie, 83(10), 969-971. doi:10.1016/s0300-9084(01)01329-3Kwok, S. F., Staub, J. M., & Deng, X.-W. (1999). Characterization of two subunits of Arabidopsis 19S proteasome regulatory complex and its possible interaction with the COP9 complex 1 1Edited by J. Karn. Journal of Molecular Biology, 285(1), 85-95. doi:10.1006/jmbi.1998.2315Nezames, C. D., & Deng, X. W. (2012). The COP9 Signalosome: Its Regulation of Cullin-Based E3 Ubiquitin Ligases and Role in Photomorphogenesis. Plant Physiology, 160(1), 38-46. doi:10.1104/pp.112.198879Moon, J., Parry, G., & Estelle, M. (2004). The Ubiquitin-Proteasome Pathway and Plant Development. The Plant Cell, 16(12), 3181-3195. doi:10.1105/tpc.104.161220Dreher, K., & Callis, J. (2007). Ubiquitin, Hormones and Biotic Stress in Plants. Annals of Botany, 99(5), 787-822. doi:10.1093/aob/mcl255Parry, G., & Estelle, M. (2004). Regulation of cullin-based ubiquitin ligases by the Nedd8/RUB ubiquitin-like proteins. Seminars in Cell & Developmental Biology, 15(2), 221-229. doi:10.1016/j.semcdb.2003.12.003Wee, S., Geyer, R. K., Toda, T., & Wolf, D. A. (2005). CSN facilitates Cullin–RING ubiquitin ligase function by counteracting autocatalytic adapter instability. Nature Cell Biology, 7(4), 387-391. doi:10.1038/ncb1241Kuramata, M., Masuya, S., Takahashi, Y., Kitagawa, E., Inoue, C., Ishikawa, S., … Kusano, T. (2008). Novel Cysteine-Rich Peptides from Digitaria ciliaris and Oryza sativa Enhance Tolerance to Cadmium by Limiting its Cellular Accumulation. Plant and Cell Physiology, 50(1), 106-117. doi:10.1093/pcp/pcn175Zeng, W., Melotto, M., & He, S. Y. (2010). Plant stomata: a checkpoint of host immunity and pathogen virulence. Current Opinion in Biotechnology, 21(5), 599-603. doi:10.1016/j.copbio.2010.05.006Wigge, P. A. (2011). FT, A Mobile Developmental Signal in Plants. Current Biology, 21(9), R374-R378. doi:10.1016/j.cub.2011.03.038Kardailsky, I. (1999). Activation Tagging of the Floral Inducer FT. Science, 286(5446), 1962-1965. doi:10.1126/science.286.5446.1962Srikanth, A., & Schmid, M. (2011). Regulation of flowering time: all roads lead to Rome. Cellular and Molecular Life Sciences, 68(12), 2013-2037. doi:10.1007/s00018-011-0673-yGalvao, V. C., Horrer, D., Kuttner, F., & Schmid, M. (2012). Spatial control of flowering by DELLA proteins in Arabidopsis thaliana. Development, 139(21), 4072-4082. doi:10.1242/dev.080879Cerdán, P. D., & Chory, J. (2003). Regulation of flowering time by light quality. Nature, 423(6942), 881-885. doi:10.1038/nature01636Guo, H. (1998). Regulation of Flowering Time by Arabidopsis Photoreceptors. Science, 279(5355), 1360-1363. doi:10.1126/science.279.5355.1360Liu, B., Zuo, Z., Liu, H., Liu, X., & Lin, C. (2011). Arabidopsis cryptochrome 1 interacts with SPA1 to suppress COP1 activity in response to blue light. Genes & Development, 25(10), 1029-1034. doi:10.1101/gad.2025011Weidler, G., zur Oven-Krockhaus, S., Heunemann, M., Orth, C., Schleifenbaum, F., Harter, K., … Batschauer, A. (2012). Degradation of Arabidopsis CRY2 Is Regulated by SPA Proteins and Phytochrome A. The Plant Cell, 24(6), 2610-2623. doi:10.1105/tpc.112.09821

The serine-rich N-terminal region of Arabidopsis phytochrome A is required for protein stability.

Deletion or substitution of the serine-rich N-terminal stretch of grass phytochrome A (phyA) has repeatedly been shown to yield a hyperactive photoreceptor when expressed under the control of a constitutive promoter in transgenic tobacco or Arabidopsis seedlings retaining their native phyA. These observations have lead to the proposal that the serine-rich region is involved in negative regulation of phyA signaling. To re-evaluate this conclusion in a more physiological context we produced transgenic Arabidopsis seedlings of the phyA-null background expressing Arabidopsis PHYA deleted in the sequence corresponding to amino acids 6-12, under the control of the native PHYA promoter. Compared to the transgenic seedlings expressing wild-type phyA, the seedlings bearing the mutated phyA showed normal responses to pulses of far-red (FR) light and impaired responses to continuous FR light. In yeast two-hybrid experiments, deleted phyA interacted normally with FHY1 and FHL, which are required for phyA accumulation in the nucleus. Immunoblot analysis showed reduced stability of deleted phyA under continuous red or FR light. The reduced physiological activity can therefore be accounted for by the enhanced destruction of the mutated phyA. These findings do not support the involvement of the serine-rich region in negative regulation but they are consistent with a recent report suggesting that phyA turnover is regulated by phosphorylation