Identification and Characterisation of HIR Reaction Modules Involved in Phytochrome A Signalling
Final Report Abstract
Phytochromes are red/far-red light receptors in plants that play an important role in regulation of growth and development and the adaptation to the ambient environment. Gene duplication events during evolution of seed plants resulted in small gene families coding for phytochromes in today’s land plants. Phytochrome A (phyA) and B (phyB) are the primary phytochromes in seed plants. The absorption spectra of phyA and phyB are virtually identical and suggest a function as red light receptors. phyB behaves as expected and is activated by red light. In contrast, phyA has an action peak in far-red light, where phytochromes would be expected to be less active than in red light. We have previously shown that the mechanism by which lightactivated phyA is transported into the nucleus contributes to shaping its action spectrum. However, these studies have also shown that additional mechanisms exist that are essential to obtain the full red→far-red shift of the phyA action peak. This shift is important for induction of germination and seedling establishment in strong canopy shade. Here, we investigated potential mechanism that could shift the peak of the phyA action spectrum to far-red light. The key finding is that phytochrome dimers consisting of two active phytochromes (homodimers) and such consisting of one active and one inactive phytochrome (heterodimers) behave differently and that the different behaviour could account for the different action spectra of phyA and phyB. We measured different properties of phyA, such as degradation and dark reversion, under light conditions generating predominantly homo- or heterodimers. These data are currently being used to test a mathematical model to explain the shift of the phyA action peak from red to far-red light.
Publications
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(2015). High-level expression and phosphorylation of phytochrome B modulates flowering time in Arabidopsis. Plant J. 83: 794–805
Hajdu, A., Ádám, É., Sheerin, D.J., Dobos, O., Bernula, P., Hiltbrunner, A., Kozma- Bognár, L., and Nagy, F.
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(2015). Systematic analysis of how phytochrome B dimerization determines its specificity. Nat. Plants 1: 15090
Klose, C., Venezia, F., Hussong, A., Kircher, S., Schäfer, E., and Fleck, C.
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(2016). Characterization of photomorphogenic responses and signaling cascades controlled by phytochrome-A expressed in different tissues. New Phytol. 211: 584–598
Kirchenbauer, D., Viczián, A., Ádám, É., Hegedűs, Z., Klose, C., Leppert, M., Hiltbrunner, A., Kircher, S., Schäfer, E., and Nagy, F.
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(2016). Phytochrome B integrates light and temperature signals in Arabidopsis. Science 354: 897–900
Legris, M., Klose, C., Burgie, E.S., Rojas, C.C.R., Neme, M., Hiltbrunner, A., Wigge, P.A., Schäfer, E., Vierstra, R.D., and Casal, J.J.
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(2016). Phytochromes function as thermosensors in Arabidopsis. Science 354: 886–889
Jung, J.-H., Domijan, M., Klose, C., Biswas, S., Ezer, D., Gao, M., Khattak, A.K., Box, M.S., Charoensawan, V., Cortijo, S., Kumar, M., Grant, A., Locke, J.C.W., Schäfer, E., Jaeger, K.E., Wigge, P.A.
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(2016). Phytochromes: More than meets the eye. Trends Plant Sci. 21: 543–546
Rensing, S.A., Sheerin, D.J., and Hiltbrunner, A.
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(2016). SPA proteins: SPAnning the gap between visible light and gene expression. Planta 244: 297–312
Menon, C., Sheerin, D.J., and Hiltbrunner, A.
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(2017). Molecular mechanisms and ecological function of far-red light signalling. Plant Cell Environ.
Sheerin, D.J. and Hiltbrunner, A.
