Diurnal dependence of growth responses to shade in Arabidopsis: role of hormone, clock, and light signaling.
We investigated the diurnal dependence of the hypocotyl-growth responses to shade under sunlight-night cycles in Arabidopsis thaliana. Afternoon shade events promoted hypocotyl growth, while morning shade was ineffective. The lhy-D, elf3, lux, pif4 pif5, toc1, and quadruple della mutants retained the response to afternoon shade and the lack of response to morning shade while the lhy cca1 mutant responded to both morning and afternoon shade. The phyB mutant, plants overexpressing the multidrug resistance-like membrane protein ABCB19, and the iaa17/axr3 loss-of-function mutant failed to respond to shade. Transient exposure of sunlight-grown seedlings to synthetic auxin in the afternoon caused a stronger promotion of hypocotyl growth than morning treatments. The promotion of hypocotyl growth by afternoon shade or afternoon auxin required light perceived by phytochrome A or cryptochromes during the previous hours of the photoperiod. Although the ELF4-ELF3-LUX complex, PIF4, PIF5, and DELLA are key players in the generation of diurnal hypocotyl-growth patterns, they exert a minor role in the control of the diurnal pattern of growth responses to shade. We conclude that the strong diurnal dependency of hypocotyl-growth responses to shade relates to the balance between the antagonistic actions of LHY-CCA1 and a light-derived signal.
IFEVA, Facultad de Agronomía, Universidad de Buenos Aires and Consejo Nacional de Investigaciones Científicas y Técnicas, Av. San Martín 4453, 1417 Buenos Aires, Argentina.
Romina
R
Sellaro
Manuel
M
Pacín
Jorge J
JJ
Casal
D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000254:growth & development* / Q000528:radiation effects*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D057906:Circadian Clocks / Q000187:drug effects / Q000528:radiation effects*; D002940:Circadian Rhythm / Q000187:drug effects / Q000235:genetics / Q000528:radiation effects*; D003624:Darkness; D018506:Gene Expression Regulation, Plant / Q000187:drug effects / Q000528:radiation effects; D018546:Hypocotyl / Q000187:drug effects / Q000254:growth & development / Q000528:radiation effects; D007210:Indoleacetic Acids / Q000378:metabolism / Q000494:pharmacology; D008027:Light; D009154:Mutation / Q000235:genetics; D017440:Photoperiod; D051939:Phytochrome B / Q000378:metabolism; D010846:Picloram / Q000494:pharmacology; D010937:Plant Growth Regulators / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics / Q000528:radiation effects*
D029681:Arabidopsis Proteins; D007210:Indoleacetic Acids; D010937:Plant Growth Regulators; D051939:Phytochrome B; D010846:Picloram