Phytochrome A and B Regulate Primary Metabolism in Arabidopsis Leaves in Response to Light.

Xiaozhen Han,Takayuki Tohge,Ronan Sulpice,Pierce Lalor,Nicholas Devaney,Alberto A Esteves-Ferreira,Alisdair R Fernie,Peter Dockery

doi:10.3389/fpls.2017.01394

Abstract

Primary metabolism is closely linked to plant productivity and quality. Thus, a better understanding of the regulation of primary metabolism by photoreceptors has profound implications for agricultural practices and management. This study aims at identifying the role of light signaling in the regulation of primary metabolism, with an emphasis on starch. We first screened seven cryptochromes and phytochromes mutants for starch phenotype. The phyAB mutant showed impairment in starch accumulation while its biomass, chlorophyll fluorescence parameters, and leaf anatomy were unaffected, this deficiency being present over the whole vegetative growth period. Mutation of plastidial nucleoside diphosphate kinase-2 (NDPK2), acting downstream of phytochromes, also caused a deficit in starch accumulation. Besides, the glucose-1-phosphate adenylyltransferase small subunit (APS1) was down-regulated in phyAB. Those results suggest that PHYAB affect starch accumulation through NDPK2 and APS1. Then, we determined changes in starch and primary metabolites in single phyA, single phyB, double phyAB grown in light conditions differing in light intensity and/or light spectral content. PHYA is involved in starch accumulation in all the examined light conditions, whereas PHYB only exhibits a role under low light intensity (44 ± 1 μmol m-2 s-1) or low R:FR (11.8 ± 0.6). PCA analysis of the metabolic profiles in the mutants and wild type (WT) suggested that PHYB acts as a major regulator of the leaf metabolic status in response to light intensity. Overall, we propose that PHYA and PHYB signaling play essential roles in the control of primary metabolism in Arabidopsis leaves in response to light.

Highlights

Plants possess a number of photoreceptor proteins which perceive light signals and modify a myriad of physiological processes in plants (Briggs and Olney, 2001; Fankhauser and Staiger, 2002; Moglich et al, 2010)
Hy1/cry1 and hy1/cry1/cry2 mutants were significantly higher for Y(NPQ), which means more energy was dissipated by regulated heat dissipation in those mutants compared to their respective wild type (WT) (Supplementary Table 3)
We investigated the role of photoreceptors in the regulation of primary metabolism, with a particular emphasis on starch accumulation. cry1 and cry2 single mutants did not show any significant difference in starch accumulation from WT (Figure 1), and did not show impaired photosystem II (Supplementary Table 3) and retarded growth phenotype (Supplementary Figure 1)

Summary

Introduction

Plants possess a number of photoreceptor proteins which perceive light signals and modify a myriad of physiological processes in plants (Briggs and Olney, 2001; Fankhauser and Staiger, 2002; Moglich et al, 2010). Phytochromes (PHYs) and cryptochromes (CRYs) are two major classes of photoreceptors which control over similar aspects of plant development such as de-etiolation, Phytochromes Regulate Primary Metabolism plant architecture and flowering (Franklin and Quail, 2010; Yu et al, 2010). Phytochromes are formed of a chromophore and an apoprotein (Jones et al, 1986) They have two photoconvertible forms: the red absorbing form Pr and the far-red form Pfr (Lagarias and Rapoport, 1980). PHYA protein accumulates to a high level in etiolated seedlings and acts primarily as a far-red sensor at the stages of early seedling development (Parks and Quail, 1993), whereas PHYB is the predominant red sensor (Reed et al, 1993; Franklin et al, 2003). Hypocotyl 1 (HY1) encodes a plastid heme oxygenase necessary for PHY chromophore biosynthesis, and deletion of HY1 leads to lowered levels of photoreversible PHY A, B, C, D, E, reduced sensitivity to far-red and red light (Chory et al, 1989; Muramoto et al, 1999)

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