Phytochromes, Cryptochromes, Phototropin: Photoreceptor Interactions in Plants

Abstract

In higher plants, natural radiation simultaneously activates more than one photoreceptor. Five phytochromes (phyA through phyD), two cryptochromes (cry1, cry2) and phototropin have been identified in the model species Arabidopsis thaliana. There is light-dependent epistasis among certain photoreceptor genes because the action of one pigment can be affected by the activity of others. Under red light, phyA and phyB are antagonistic, but under far-red light, followed by brief red light, phyA and phyB are synergistic in the control of seedling morphology and the expression of some genes during de-etiolation. Under short photoperiods of red and blue light, cry1 and phyB are synergistic, but under continuous exposure to the same light field the actions of phyB and cry1 become independent and additive. Phototropic bending of the shoot toward unilateral blue light is mediated by phototropin, but cry1, cry2, phyA and phyB positively regulate the response. Finally, cry2 and phyB are antagonistic in the induction of flowering. At least some of these interactions are likely to result from cross talk of the photoreceptor signaling pathways and uncover new avenues to approach signal transduction. Experiments under natural radiation are beginning to show that the interactions create a phototransduction network with emergent properties. This provides a more robust system for light perception in plants. PLANT PHOTORECEPTORSPlants are able to monitor the light environment and perceive signals that modulate growth and development. Seed germination, seedling de-etiolation (i.e. transition from skotomorphogenesis to photomorphogenesis), vegetative growth, organ orientation and the transition to reproductive development are some of the processes profoundly affected by the light environment via nonphotosynthetic light signals. These signals are perceived by a number of photoreceptors:

KIDARI, Encoding a Non-DNA Binding bHLH Protein, Represses Light Signal Transduction in Arabidopsis thaliana

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Light signaling and plant responses to blue and UV radiations—Perspectives for applications in horticulture

“…Downstream of crys and phots, COP1 regulates the stomatal response to blue light (Mao et al, 2005;Wang et al, 2010a), but how it participates in this regulation remains unknown . Phytochromes enhance cry and phot activity (Casal, 2000). In Arabidopsis, stomata of the triple mutants cry1 cry2 phyB, phot1 phot2 phyB or cry1 phyA phyB open less than those of the single or double mutants under white light.…”

Light based cellular interactions: hypotheses and perspectives

“…Since interacting pathways are something absolutely common in biology, the assumption that the pathways of two or more photoreceptors are interacting, is not unreasonable. We should not omit the fact that interacting pathways of photoreceptors have already been observed in plants [73].…”