Metagenome-assembled genomes from sugarcane mill mud.

The genomes of 11 bacteria and 3 archaea were assembled from metagenomic DNA extracted from sugarcane mill mud. These metagenome-assembled genomes ranged from 1.79 to 6.45 Mb, with 2,263 to 5,551 predicted proteins, 80.65% to 100% genome completeness, and 43.19% to 68.02% G+C content.

Multiple roles of the Cox20 chaperone in assembly of Saccharomyces cerevisiae cytochrome c oxidase.

The Cox2 subunit of Saccharomyces cerevisiae cytochrome c oxidase is synthesized in the mitochondrial matrix as a precursor whose leader peptide is rapidly processed by the inner membrane protease following translocation to the intermembrane space. Processing is chaperoned by Cox20, an integral inner membrane protein whose hydrophilic domains are located in the intermembrane space, and Cox20 remains associated with mature, unassembled Cox2. The Cox2 C-tail domain is exported post-translationally by the highly conserved translocase Cox18 and associated proteins. We have found that Cox20 is required for efficient export of the Cox2 C-tail. Furthermore, Cox20 interacts by co-immune precipitation with Cox18, and this interaction requires the presence of Cox2. We therefore propose that Cox20 binding to Cox2 on the trans side of the inner membrane accelerates dissociation of newly exported Cox2 from the Cox18 translocase, promoting efficient cycling of the translocase. The requirement for Cox20 in cytochrome c oxidase assembly and respiratory growth is partially bypassed by yme1, mgr1 or mgr3 mutations, each of which reduce i-AAA protease activity in the intermembrane space. Thus, Cox20 also appears to stabilize unassembled Cox2 against degradation by the i-AAA protease. Pre-Cox2 leader peptide processing by Imp1 occurs in the absence of Cox20 and i-AAA protease activity, but is greatly reduced in efficiency. Under these conditions some mature Cox2 is assembled into cytochrome c oxidase allowing weak respiratory growth. Thus, the Cox20 chaperone has important roles in leader peptide processing, C-tail export, and stabilization of Cox2.

Genetic architecture of mitochondrial editing in Arabidopsis thaliana.

We have analyzed the mitochondrial editing behavior of two Arabidopsis thaliana accessions, Landsberg erecta (Ler) and Columbia (Col). A survey of 362 C-to-U editing sites in 33 mitochondrial genes was conducted on RNA extracted from rosette leaves. We detected 67 new editing events in A. thaliana rosette leaves that had not been observed in a prior study of mitochondrial editing in suspension cultures. Furthermore, 37 of the 441 C-to-U editing events reported in A. thaliana suspension cultures were not observed in rosette leaves. Forty editing sites that are polymorphic in extent of editing were detected between Col and Ler. Silent editing sites, which do not change the encoded amino acid, were found in a large excess compared to nonsilent sites among the editing events that differed between accessions and between tissue types. Dominance relationships were assessed for 15 of the most polymorphic sites by evaluating the editing values of the reciprocal hybrids. Dominance is more common in nonsilent sites than in silent sites, while additivity was observed only in silent sites. A maternal effect was detected for 8 sites. QTL mapping with recombinant inbred lines detected 12 major QTL for 11 of the 13 editing traits analyzed, demonstrating that efficiency of editing of individual mitochondrial C targets is generally governed by a major factor.