Blue-light induced biosynthesis of ROS contributes to the signaling mechanism of Arabidopsis cryptochrome

Mohamed El-Esawi,Louis-David Arthaut,Justin Link,Carlos F Martino,Nathalie Jourdan,Margaret Ahmad,Alain D’Harlingue

doi:10.1038/s41598-017-13832-z

Abstract

Cryptochromes are evolutionarily conserved blue light receptors with many roles throughout plant growth and development. They undergo conformational changes in response to light enabling interaction with multiple downstream signaling partners. Recently, it has been shown that cryptochromes also synthesize reactive oxygen species (ROS) in response to light, suggesting the possibility of an alternate signaling mechanism. Here we show by fluorescence imaging and microscopy that H202 and ROS accumulate in the plant nucleus after cryptochrome activation. They induce ROS-regulated transcripts including for genes implicated in pathogen defense, biotic and abiotic stress. Mutant cryptochrome alleles that are non-functional in photomorphogenesis retain the capacity to induce ROS-responsive phenotypes. We conclude that nuclear biosynthesis of ROS by cryptochromes represents a new signaling paradigm that complements currently known mechanisms. This may lead to novel applications using blue light induced oxidative bursts to prime crop plants against the deleterious effects of environmental stresses and toxins.

Highlights

Cryptochromes are blue light sensing receptors that regulate multiple processes of plant growth and development, including photomorphogenesis, de-etiolation, flowering initiation, stress response, and hormone signaling[1,2,3]
Prior studies have shown that an increase in levels of reactive oxygen species (ROS) can be observed within minutes of blue light illumination in the nuclei of Sf21 insect cell cultures expressing recombinant Arabidopsis cryptochromes[16,17]
We show that there is a visible accumulation of ROS in Arabidopsis seedlings as a result of cryptochrome activation by light (Fig. 2)

Summary

Introduction

Cryptochromes are blue light sensing receptors that regulate multiple processes of plant growth and development, including photomorphogenesis, de-etiolation, flowering initiation, stress response, and hormone signaling[1,2,3] They are localized in the nucleus and function both directly and indirectly as core regulators of more than 20% of total cellular transcripts[4,5,6]. Arabidopsis cryptochromes interact with protein partners including phytochromes (PhyA and PhyB), the WD-repeat protein SPA1, the E3 ubiquitin ligase COP1, and bHLH transcription factors CIB1,2, PIF3 and PIF48,9 which have a signaling role in photomorphogenesis or flowering initiation Most of these partners attach to the PHR domain and release the CCE domain from the protein surface[10,11].

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