title: Phytochrome B Nuclear Bodies Respond to the Low Red to Far-Red Ratio and to the Reduced Irradiance of Canopy Shade in Arabidopsis.
abstract: The current consensus is that plant responses to canopy shade involve the perception of low red to far-red ratios (R:FRs) by phytochrome B (phyB), which leads to the direct activation of auxin synthesis genes by PHYTOCHROME INTERACTING FACTORs (PIFs). In addition to its effect on R:FRs, shade also reduces irradiance, but whether shade-induced drops in irradiance affect phyB activity has not been demonstrated. To address this issue, we investigated whether irradiance and R:FRs have similar effects on the nuclear distribution of phyB in petiole cells of light-grown plants. Under high-irradiance white light, phyB formed large nuclear bodies. Lowering irradiance without changing R:FRs or lowering R:FRs by adding far-red light led to the appearance of small nuclear bodies containing phyB. Large nuclear bodies remained but with some concomitant reduction in diameter. The appearance of small nuclear bodies was rapid, stable, and reversible upon the return to high irradiance and high R:FRs. High levels of red light but not of blue light were enough to restrain the formation of small phyB nuclear bodies. Irradiance was effective within the range found in natural canopies and even under relatively low R:FRs. The promotion of leaf hyponasty by lowering irradiance was impaired in phyB and pif mutants, as previously reported for the response to R:FRs. The expression of auxin-related genes showed a similar hierarchy of response to low R:FRs and low irradiance. We propose that phyB is able to perceive not only the low R:FRs, but also the low irradiance of shade.
authors.affiliation: Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura, Facultad de Agronomía, Universidad de Buenos Aires, and Consejo Nacional de Investigaciones Científicas y Técnicas, 1417 Buenos Aires, Argentina (S.A.T., A.S.B., M.B.T.R., J.J.C.); andFundación Instituto Leloir, Instituto de Investigaciones Bioquímicas de Buenos Aires-Consejo Nacional de Investigaciones Científicas y Técnicas, C1405BWE Buenos Aires, Argentina (M.L., J.J.C.).
authors.forename: Santiago Ariel
authors.initials: SA
authors.lastname: Trupkin
authors.affiliation: Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura, Facultad de Agronomía, Universidad de Buenos Aires, and Consejo Nacional de Investigaciones Científicas y Técnicas, 1417 Buenos Aires, Argentina (S.A.T., A.S.B., M.B.T.R., J.J.C.); andFundación Instituto Leloir, Instituto de Investigaciones Bioquímicas de Buenos Aires-Consejo Nacional de Investigaciones Científicas y Técnicas, C1405BWE Buenos Aires, Argentina (M.L., J.J.C.).
authors.forename: Martina
authors.initials: M
authors.lastname: Legris
authors.affiliation: Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura, Facultad de Agronomía, Universidad de Buenos Aires, and Consejo Nacional de Investigaciones Científicas y Técnicas, 1417 Buenos Aires, Argentina (S.A.T., A.S.B., M.B.T.R., J.J.C.); andFundación Instituto Leloir, Instituto de Investigaciones Bioquímicas de Buenos Aires-Consejo Nacional de Investigaciones Científicas y Técnicas, C1405BWE Buenos Aires, Argentina (M.L., J.J.C.).
authors.forename: Ana Sabrina
authors.initials: AS
authors.lastname: Buchovsky
authors.affiliation: Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura, Facultad de Agronomía, Universidad de Buenos Aires, and Consejo Nacional de Investigaciones Científicas y Técnicas, 1417 Buenos Aires, Argentina (S.A.T., A.S.B., M.B.T.R., J.J.C.); andFundación Instituto Leloir, Instituto de Investigaciones Bioquímicas de Buenos Aires-Consejo Nacional de Investigaciones Científicas y Técnicas, C1405BWE Buenos Aires, Argentina (M.L., J.J.C.).
authors.forename: María Belén
authors.initials: MB
authors.lastname: Tolava Rivero
authors.affiliation: Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura, Facultad de Agronomía, Universidad de Buenos Aires, and Consejo Nacional de Investigaciones Científicas y Técnicas, 1417 Buenos Aires, Argentina (S.A.T., A.S.B., M.B.T.R., J.J.C.); andFundación Instituto Leloir, Instituto de Investigaciones Bioquímicas de Buenos Aires-Consejo Nacional de Investigaciones Científicas y Técnicas, C1405BWE Buenos Aires, Argentina (M.L., J.J.C.) casal@ifeva.edu.ar.
authors.forename: Jorge José
authors.identifier: http://orcid.org/0000-0001-6525-8414
authors.initials: JJ
authors.lastname: Casal