Cerdán P D, Yanovsky M J, Reymundo F C, Nagatani A, Staneloni R J, Whitelam G C, Casal J J
Instituto de Investigaciones Bioquímicas Fundación Campomar, Buenos Aires, Argentina.
Plant J. 1999 Jun;18(5):499-507. doi: 10.1046/j.1365-313x.1999.00475.x.
Phytochrome A (phyA) and phytochrome B (phyB) share the control of many processes but little is known about mutual signaling regulation. Here, we report on the interactions between phyA and phyB in the control of the activity of an Lhcb1*2 gene fused to a reporter, hypocotyl growth and cotyledon unfolding in etiolated Arabidopsis thaliana. The very-low fluence responses (VLFR) induced by pulsed far-red light and the high-irradiance responses (HIR) observed under continuous far-red light were absent in the phyA and phyA phyB mutants, normal in the phyB mutant, and reduced in the fhy1 mutant that is defective in phyA signaling. VLFR were also impaired in Columbia compared to Landsberg erecta. The low-fluence responses (LFR) induced by red-light pulses and reversed by subsequent far-red light pulses were small in the wild type, absent in phyB and phyA phyB mutants but strong in the phyA and fhy1 mutants. This indicates a negative effect of phyA and FHY1 on phyB-mediated responses. However, a pre-treatment with continuous far-red light enhanced the LFR induced by a subsequent red-light pulse. This enhancement was absent in phyA, phyB, or phyA phyB and partial in fhy1. The levels of phyB were not affected by the phyA or fhy1 mutations or by far-red light pre-treatments. We conclude that phyA acting in the VLFR mode (i.e. under light pulses) is antagonistic to phyB signaling whereas phyA acting in the HIR mode (i.e. under continuous far-red light) operates synergistically with phyB signaling, and that both types of interaction require FHY1.
光敏色素A（phyA）和光敏色素B（phyB）共同调控许多生理过程，但二者之间的信号互作调控却鲜为人知。在此，我们报道了在拟南芥黄化苗中，phyA和phyB在调控与报告基因融合的Lhcb1*2基因活性、下胚轴生长及子叶展开过程中的相互作用。phyA和phyA phyB突变体缺失由脉冲远红光诱导的极低光强反应（VLFR）以及在持续远红光下观察到的高辐照度反应（HIR），phyB突变体中这些反应正常，而在phyA信号转导存在缺陷的fhy1突变体中这些反应减弱。与Landsberg erecta相比，Columbia中VLFR也受到损害。由红光脉冲诱导并被随后的远红光脉冲逆转的低光强反应（LFR）在野生型中较小，在phyB和phyA phyB突变体中缺失，但在phyA和fhy1突变体中较强。这表明phyA和FHY1对phyB介导的反应具有负面影响。然而，持续远红光预处理增强了随后红光脉冲诱导的LFR。这种增强在phyA、phyB或phyA phyB突变体中不存在，在fhy1突变体中部分存在。phyB的水平不受phyA或fhy1突变以及远红光预处理的影响。我们得出结论，以VLFR模式起作用（即在光脉冲下）的phyA与phyB信号传导拮抗，而以HIR模式起作用（即在持续远红光下）的phyA与phyB信号传导协同作用，并且这两种相互作用类型均需要FHY1。
