Variation in dynamics of phytochrome A in Arabidopsis ecotypes and mutants

Phytochromes are photoreceptors in plants which can exist in two different conformations: the red light-absorbing form (P-r) and the far-red light-absorbing form (P-fr), depending on the light quality. The P-fr form is the physiologically active conformation. To attenuate the P-fr signal for phytochrome A (phyA), at least two different mechanisms exist: destruction of the molecule and dark reversion. Destruction is an active process leading to the degradation of P-fr. Dark reversion is the light-independent conversion of physiologically active P-fr into inactive P-r. Here, we show that dark reversion is not only an intrinsic property of the phytochrome molecule but is modulated by cellular components. Furthermore, we demonstrate that dark reversion of phyA may be observed in Arabidopsis ecotype RLD but not in other Arabidopsis ecotypes. For the first time, we have identified mutants with altered dark reversion and destruction in a set of previously isolated loss of function PHYA alleles (Xu et al. Plant Cell 1995, 7, 1433-1443). Therefore, the dynamics of the phytochrome molecule itself need to be considered during the characterization of signal transduction mutants.