Mutations of the Genomes Uncoupled 4 Gene Cause ROS Accumulation and Repress Expression of Peroxidase Genes in Rice

Rui-Qing Li; Meng Jiang; Jian-Zhong Huang; Ian Max Møller; Qing-Yao Shu

doi:10.3389/fpls.2021.682453

Mutations of the Genomes Uncoupled 4 Gene Cause ROS Accumulation and Repress Expression of Peroxidase Genes in Rice

Front Plant Sci. 2021 Jun 11:12:682453. doi: 10.3389/fpls.2021.682453. eCollection 2021.

Authors

Rui-Qing Li^{1

2}, Meng Jiang¹, Jian-Zhong Huang^{1

3}, Ian Max Møller⁴, Qing-Yao Shu^{1

3}

Affiliations

¹ Hainan Institute of Zhejiang University, Yazhou Bay Science and Technology City, Sanya, China.
² College of Agronomy, Anhui Agricultural University, Hefei, China.
³ National Key Laboratory of Rice Biology, Institute of Crop Sciences, Zhejiang University, Hangzhou, China.
⁴ Department of Molecular Biology and Genetics, Aarhus University, Slagelse, Denmark.

Abstract

The Genomes Uncoupled 4 (GUN4) is one of the retrograde signaling genes in Arabidopsis and its orthologs have been identified in oxygenic phototrophic organisms from cyanobacterium to higher plants. GUN4 is involved in tetrapyrrole biosynthesis and its mutation often causes chlorophyll-deficient phenotypes with increased levels of reactive oxygen species (ROS), hence it has been speculated that GUN4 may also play a role in photoprotection. However, the biological mechanism leading to the increased ROS accumulation in gun4 mutants remains largely unknown. In our previous studies, we generated an epi-mutant allele of OsGUN4 (gun4 ^epi ), which downregulated its expression to ∼0.5% that of its wild-type (WT), and a complete knockout allele gun4-1 due to abolishment of its translation start site. In the present study, three types of F₂ plant derived from a gun4-1/gun4 ^epi cross, i.e., gun4-1/gun4-1, gun4-1/gun4 ^epi and gun4 ^epi /gun4 ^epi were developed and used for further investigation by growing them under photoperiodic condition (16 h/8 h light/dark) with low light (LL, 100 μmol photons m^-2 s^-1) or high light (HL, 1000 μmol photons m^-2 s^-1). The expression of OsGUN4 was light responsive and had two peaks in the daytime. gun4-1/gun4-1-F₂ seeds showed defective germination and died within 7 days. Significantly higher levels of ROS accumulated in all types of OsGUN4 mutants than in WT plants under both the LL and HL conditions. A comparative RNA-seq analysis of WT variety LTB and its gun4 ^epi mutant HYB led to the identification of eight peroxidase (PRX)-encoding genes that were significantly downregulated in HYB. The transcription of these eight PRX genes was restored in transgenic HYB protoplasts overexpressing OsGUN4, while their expression was repressed in LTB protoplasts transformed with an OsGUN4 silencing vector. We conclude that OsGUN4 is indispensable for rice, its expression is light- and oxidative-stress responsive, and it plays a role in ROS accumulation via its involvement in the transcriptional regulation of PRX genes.

Keywords: GUN4; anti-oxidative response; peroxidase; reactive oxygen species; rice.