Abstract
The chloroplast is a key organelle for photosynthesis and perceiving environmental information. GENOME UNCOUPLED 4 (GUN4) has been shown to be required for the regulation of both chlorophyll synthesis, reactive oxygen species (ROS) homeostasis and plastid retrograde signaling. In this study, we found that growth of the gun4 mutant was significantly improved under medium strong light (200 μmol photons m−2s−1) compared to normal light (100 μmol photons m−2s−1), in marked contrast to wild-type (WT). Further analysis revealed that GUN4 interacts with SIGNAL RECOGNITION PARTICLE 54 KDA SUBUNIT (SRP43) and SRP54. RNA-seq analysis indicated that the expression of genes for light signaling and the circadian clock is altered in gun4 compared with (WT). qPCR analysis confirmed that the expression of the clock genes CLOCK-RELATED 1 (CCA1), LATE ELONGATION HYPOCOTYL (LHY), TIMING OF CAB EXPRESSION 1 (TOC1) and PSEUDO RESPONSE REGULATOR 7 (PRR7) is significantly changed in the gun4 and srp54 mutants under normal and medium strong light conditions. These results suggest that GUN4 may coordinate the adaptation of plants to changing light conditions by regulating the biological clock, although it is not clear whether the effect is direct or indirect.
Highlights
Chloroplasts are essential organelles for both photosynthesis and metabolic reactions [1]
The chloroplast signal recognition particle composed of the SRP43 and SRP54 subunits is involved in LHCB protein assembly and plays a vital role in chloroplast stromal
The results revealed that SRP54 interacts with GENOME UNCOUPLED 4 (GUN4) and SRP43 (Figure 1A)
Summary
Chloroplasts are essential organelles for both photosynthesis and metabolic reactions [1]. To ensure the correct functioning of chloroplasts during development and under changing environmental conditions, it is necessary to coordinate the activity of the nucleus and chloroplast genome through intracellular signaling [3]. The production of a series of key metabolites and reactive oxygen species in chloroplasts, including singlet oxygen (1 O2 ), hydrogen peroxide (H2 O2 ), superoxide anion (O2 − ) and hydroxyl radical (OH·), leads to changes in chloroplast redox state and perturbs cellular metabolic functions [26] These effects are related to redox signals, ROS, light, stress, and regulation of photosynthetic electron transport [27]. Changes in redox homeostasis may regulate the biological clock through the signaling pathway mediated by GUN4 to maintain chloroplast development and metabolic function under medium-strong light conditions. Our results suggest that GUN4 plays an important role in regulating, directly or indirectly, chloroplast redox homeostasis, chloroplast development and circadian rhythm
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