A FtsH-Like Zinc Metalloprotease, OsFtsH1, Coordinates Chloroplast Development and Photosystem II Homeostasis in Rice.

Abstract

Chloroplast development is a fundamental process underlying photosynthesis and plant growth, yet its molecular regulatory mechanisms remain to be fully elucidated. In this study, we identified an albino rice mutant, which exhibits drastically reduced chlorophyll content and defective chloroplast ultrastructure. Through map-based cloning, coupled with CRISPR/Cas9-mediated gene editing and complementation assays, we verified that the target gene encodes a zinc metalloprotease of the FtsH protein family, OsFtsH1. The expression of OsFtsH1 is light-inducible, and its encoded protein localizes specifically to chloroplasts. RNA-sequencing (RNA-seq) analysis revealed broad differential expression of photosynthesis-related genes in osftsh1 mutants. qRT-PCR further demonstrated that plastid-encoded genes involved in chloroplast biogenesis are markedly downregulated at the transcriptional level. Functional assays indicated that OsFtsH1 sustains the homeostasis of D1, D2 and CP43, core proteins of the photosystem II (PSII), and collaboratively regulates chloroplast development through interactions with three key proteins: the chloroplast signaling protein OsCPL1, the PSII oxygen-evolving complex component OsPsbO, and the photosynthetic electron transport protein OsFd1. Additionally, the expression of OsFtsH1 is induced by indole-3-acetic acid (IAA) and abscisic acid (ABA), and its overexpression markedly enhances rice sensitivity to these two phytohormones. Collectively, our findings unravel the multifaceted and crucial functions of OsFtsH1 in orchestrating chloroplast development, photosynthetic machinery homeostasis, and stress response in rice.