Abstract

Key messageBrachypodium distachyonis a good model for studying chloropla st movements in the crop plants, wheat, rye and barley. The movements are activated only by blue light, similar to Arabidopsis.Chloroplast translocations are ubiquitous in photosynthetic organisms. On the one hand, they serve to optimize energy capture under limiting light, on the other hand, they minimize potential photodamage to the photosynthetic apparatus in excess light. In higher plants chloroplast movements are mediated by phototropins (phots), blue light receptors that also control other light acclimation responses. So far, Arabidopsis thaliana has been the main model for studying the mechanism of blue light signaling to chloroplast translocations in terrestrial plants. Here, we propose Brachypodium distachyon as a model in research into chloroplast movements in C3 cereals. Brachypodium chloroplasts respond to light in a similar way to those in Arabidopsis. The amino acid sequence of Brachypodium PHOT1 is 79.3% identical, and that of PHOT2 is 73.6% identical to the sequence of the corresponding phototropin in Arabidopsis. Both phototropin1 and 2 are expressed in Brachypodium, as shown using quantitative real-time PCR. Intriguingly, the light-expression pattern of BradiPHOT1 and BradiPHOT2 is the opposite of that for Arabidopsis phototropins, suggesting potential unique light signaling in C3 grasses. To investigate if Brachypodium is a good model for studying grass chloroplast movements we analyzed these movements in the leaves of three C3 crop grasses, namely wheat, rye and barley. Similarly to Brachypodium, chloroplasts only respond to blue light in all these species.

Highlights

  • It is a truism to say that the increasing demand for global food production is one of the challenges for plant molecular biology these days

  • In Arabidopsis thaliana the photoreceptors involved in the movements are phototropin1 and phototropin2

  • The results show that phytochromes alone do not activate directional chloroplast movements in the tested species

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Summary

Introduction

It is a truism to say that the increasing demand for global food production is one of the challenges for plant molecular biology these days. Chloroplast movements depend on the direction, wavelength and intensity of light. In Arabidopsis thaliana the photoreceptors involved in the movements are phototropin (phot1) and phototropin (phot2) Both phot and phot control the accumulation response (Sakai et al 2001), but only phot controls the avoidance response (Jarillo et al 2001). Phototropins are hydrophilic and contain no obvious membrane-spanning domains they are associated with the cell membrane. They have been observed to cycle in the cell and this trafficking is believed to participate in their function (Sakamoto and Briggs 2002; Aggarwal et al 2014). In addition to chloroplast redistribution, phototropins control other acclimation movements including phototropism (Sakai et al 2001), stomatal opening (Kinoshita et al 2001), nuclear avoidance movement (Iwabuchi et al 2007) and leaf flattening (Inoue et al 2008)

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