Phytochrome B-mediated activation of lipoxygenase modulates an excess red light-induced defence response in Arabidopsis.

Yuanyuan Zhao,Da Xing,Jun Zhou

doi:10.1093/jxb/eru247

Abstract

Lipoxygenase (LOX), a non-haem-iron-containing dioxygenase, is activated under various biotic or abiotic stresses to trigger a series resistance response, but the molecular mechanism of LOX activation remains unclear. This work investigated the activation of LOX during the plant defence response induced by excess red light (RL). In conditions of RL-induced defence, Arabidopsis LOX activity and transcription levels of LOX2, LOX3, and LOX4 were both upregulated. Under RL, phytochrome B promoted the degradation of phytochrome-interacting factor 3 (PIF3), a factor that inhibited the expression levels of LOXs, and thus the transcription levels of LOX2, LOX3, and LOX4 were increased. Upon pathogen infection, the activity of mitogen-activated protein kinase 3 (MPK3) and MPK6 was increased in plants pre-treated with RL. Moreover, experiments with the inhibitor PD98059 and mutants mpk3 and mpk6-2 demonstrated that MPK3 and MPK6 were both responsible for LOX activation. Further results showed that, in response to RL, an increase in cytoplasmic calcium concentration and upregulation of calmodulin 3 (CaM3) transcript level occurred upstream of MPK3 and MPK6 activation. Collectively, these results suggested that activation of LOX both at the transcript level and in terms of activity modulates the defence response induced by RL, providing a new insight into the mechanistic study of LOX during plant defences.

Highlights

Plants, as sedentary organisms, have evolved a high flexibility in both metabolism and development to cope with the multiple environmental stimuli that they are exposed to (Genoud et al, 2002)
Arabidopsis ecotype Columbia-0 (Col-0) and seeds of mutants Phytochrome B (phyB), mpk3, and mpk6-2 were obtained from the European Arabidopsis Stock Centre. phyB-ox-YFP (Wang FF et al, 2010), pif3 and pif3-oxYFP (Soy et al, 2012) were sterilized and grown on solid Murashige and Skoog medium as described previously (Zhang and Xing, 2008). 4,′(2, 3-Dimethyltetramethylene)dipyrocatechol (NDGA) was Activation of LOX modulates excess red light-induced defence response | 4909 obtained from Merk, linoleic acid, 1,2-bis(2-aminophenoxy)ethaneN,N,N′,N′-tetra-acetic acid (BAPTA-AM), and PD98059 were purchased from Sigma-Aldrich
When Arabidopsis plants were inoculated with virulent Pseudomonas syringae pv. tomato (Pst)-DC3000, the WT plant leaves under normal light conditions turned yellow and wilted and died (Fig. 1A), whereas plants pre-irradiated with excess white light (EL) (1500 μmol m–2 s–1 for 1 h) or excess red light (RL) (120 μmol m–2 s–1 for 4 h; 660–680 nm) showed minute yellow disease lesions at 3 d post-inoculation

Summary

Introduction

As sedentary organisms, have evolved a high flexibility in both metabolism and development to cope with the multiple environmental stimuli that they are exposed to (Genoud et al, 2002). Light signalling is fundamental to the growth and development of plants. Certain irradiation with moderate EL can enhance the plant defence response, and red light (RL) plays a major role (Szechyńska-Hebda et al, 2010). Phytochrome B (phyB), as the main receptor of RL, is essential for this process. Szechyńska-Hebda et al (2010) found that photo-electrophysiological signalling is a component of signalling cascades that potentially regulates the defence response. The mechanisms mediating the defence response by phyB are still unclear. Plants monitor informational light signals from their surroundings using a range of sensory photoreceptors including phototrophin, crytochrome, and phytochrome (Leivar et al, 2012).

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