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Protein aggregation in plant mitochondria lacking Lon1 inhibits translation and induces unfolded protein responses

ABSTRACT: Loss of Lon1 led to stunted plant growth and accumulation of nuclear‐encoded mitochondrial proteins including Lon1 substrates. However, an in‐depth label‐free proteomics quantification of mitochondrial proteins in lon1 revealed that the majority of mitochondrial‐encoded proteins decreased in abundance. Additionally, we found that lon1 mutants contained protein aggregates in the mitochondrial that were enriched in metabolic enzymes, ribosomal subunits and PPR‐containing proteins of the translation apparatus. These mutants exhibited reduced general mitochondrial translation as well as deficiencies in RNA splicing and editing. These findings support the role of Lon1 in maintaining a functional translational apparatus for mitochondrial‐encoded gene translation. Transcriptome analysis of lon1 revealed a mitochondrial unfolded protein response reminiscent of the mitochondrial retrograde signalling dependent on the transcription factor ANAC017. Notably, lon1 mutants exhibited transiently elevated ethylene production, and the shortened hypocotyl observed in lon1 mutants during skotomorphogenesis was partially alleviated by ethylene inhibitors. Furthermore, the short root phenotype was partially ameliorated by introducing a mutation in the ethylene receptor ETR1. Interestingly, the upregulation of only a select few target genes was linked to ETR1‐mediated ethylene signalling. Together this provides multiple steps in the link between loss of Lon1 and signalling responses to restore mitochondrial protein homoeostasis in plants.

INSTRUMENT(S): Orbitrap Exploris 240

ORGANISM(S): Arabidopsis Thaliana (mouse-ear Cress)

TISSUE(S): Plant Cell, Seedling

DISEASE(S): Disease Free

SUBMITTER: Ce Song

LAB HEAD: Lei Li

PROVIDER: PXD038026 | Pride | 2024-07-08

REPOSITORIES: Pride

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Project description:Arabidopsis Lon1 serves dual roles as a mitochondrial protease and chaperone. Loss of Lon1 function reduced autophagy flux at transcriptional, protein and cellular levels. Meanwhile, changes occurred in the levels of cellular subunit proteins, especially a significant upregulation of mitochondrial proteins overall in lon1 mutants. Lon1 is a key enzyme in maintaining mitochondrial protein homeostasis. In lon1 mutants, other mitochondrial proteases including mitochondrial autophagy receptor proteins showed significant increases in abundance. Mitophagy is an important mechanism for cellular quality control. lon1-2atg5-1 double mutant were constructed to investigate how they cooperatively regulate mitochondrial protein homeostasis. Transcriptome sequencing results revealed that Lon1 inactivation led to widespread unfolded protein responses (UPRs) pathway activation in lon1-2atg5-1, consistent with lon1-2, while loss function of ATG5 inactivation did not affect mitochondrial homeostasis. The double mutant also exhibited independent plant phenotypes from single parents, yet more severe seed number and embryo development issues, suggesting an additive effect of lon1-2 and atg5-1. Protein Storage Vacuole (PSV) and oil body phenotypes also showed more severe developmental damage in the double mutants. Brassinosteroid (BR) acts as a key plant hormone controlling seed and embryo development. GO and KEGG analysis of genes simultaneously downregulated in lon1-2, atg5-1, and lon1-2atg5-1 revealed significant downregulation of genes involved in BR biosynthesis and its homeostasis, indicating that this may be one of the key factors leading to abnormal seed and embryo development in the mutants. In general, the loss function of Lon1 reduces autophagy flux and induces UPRs to regulate protein homeostasis. Meanwhile, the simultaneous absence of Lon1 and autophagy significantly down-regulates the expression of genes related to BR biosynthesis and homeostasis, thereby leading to pronounced blockage in the development of double mutant seeds and embryos.

			Action	DRS
	PD_Total_Protein.msf	Msf
	WT_Total_Protein_1.raw	Raw
	WT_Total_Protein_2.raw	Raw
	WT_Total_Protein_3.raw	Raw
	checksum.txt	Txt

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Protein aggregation in plant mitochondria lacking Lon1 inhibits translation and induces unfolded protein responses

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