To obtain a global overview of how mitochondria respond to stress, we aimed to define the plant mitochondrial stress response (MSR). By combining a set of 1196 Arabidopsis thaliana genes that putatively encode mitochondrial proteins with 16 microarray experiments on stress-related conditions, 45 nuclear encoded genes were defined as widely stress-responsive. Using green fluorescent protein (GFP) fusion assays, the mitochondrial targeting of a large number of these proteins was tested, confirming in total 26 proteins as mitochondrially targeted. Several of these proteins were observed to be dual targeted to mitochondria and plastids, including the small heat shock proteins sHSP23.5 and sHSP23.6. In addition to the well defined stress components of mitochondria, such as alternative oxidases, nicotinamide adenine dinucleotide (NAD(P)H) dehydrogenases, and heat shock proteins, a variety of other proteins, many with unknown function, were identified. The mitochondrial carrier protein family was over-represented in the stress-responsive genes, suggesting that stress induces altered needs for metabolite transport across the mitochondrial inner membrane. Although the genes encoding many of these proteins contain common cis-acting regulatory elements, it was apparent that a number of distinct regulatory processes or signals likely triggered the MSR. Therefore, these genes provide new model systems to study mitochondrial retrograde regulation, in addition to the widely used alternative oxidase model. Additionally, as changes in proteins responsive to stress did not correlate well with changes at a transcript level, it suggests that post-transcriptional mechanisms also play an important role in defining the MSR.

SUMMARYWe have identified a mitochondrial protein (RUG3) that is required for accumulation of mitochondrial respiratory chain complex I. RUG3 is related to human REGULATOR OF CHROMOSOME CONDENSATION 1 (RCC1) and Arabidopsis UV-B RESISTANCE 8 (UVR8). Although the family of RCC1-like proteins in Arabidopsis has over 20 members, UVR8 is the sole plant representative of this family to have been functionally characterized. Mitochondria from Arabidopsis plants lacking a functional RUG3 gene showed greatly reduced complex I abundance and activity. In contrast, accumulation of complexes III, IV and V of the oxidative phosphorylation system and the capacity for succinate-dependent respiration were unaffected. A comprehensive study of processes contributing to complex I biogenesis in rug3 mutants revealed that RUG3 is required for efficient splicing of the nad2 mRNA, which encodes a complex I subunit. A comparison of the formation of complex I assembly intermediates between rug3 and wild type mitochondria indicated that NAD2 enters the assembly pathway at an early stage. Remarkably, rug3 mutants displayed increased capacities for import of nucleus-encoded mitochondrial proteins into the organelle and showed moderately increased mitochondrial transcript levels. This observation is consistent with global transcript changes indicating enhanced mitochondrial biogenesis in the rug3 mutant in response to the complex I defect.

The expression of a variety of nuclear genes encoding mitochondrial proteins is known to adapt to changes in environmental conditions and retrograde signaling. The presence of putative WRKY transcription factor binding sites (W-boxes) in the promoters of many of these genes prompted a screen of 72 annotated WRKY factors in the Arabidopsis (Arabidopsis thaliana) genome for regulators of transcripts encoding mitochondrial proteins. A large-scale yeast one-hybrid screen was used to identify WRKY factors that bind the promoters of marker genes (Alternative oxidase1a, NADH dehydrogenaseB2, and the AAA ATPase Ubiquinol-cytochrome c reductase synthesis1), and interactions were confirmed using electromobility shift assays. Transgenic overexpression and knockout lines for 12 binding WRKY factors were generated and tested for altered expression of the marker genes during normal and stress conditions. AtWRKY40 was found to be a repressor of antimycin A-induced mitochondrial retrograde expression and high-light-induced signaling, while AtWRKY63 was identified as an activator. Genome-wide expression analysis following high-light stress in transgenic lines with perturbed AtWRKY40 and AtWRKY63 function revealed that these factors are involved in regulating stress-responsive genes encoding mitochondrial and chloroplast proteins but have little effect on more constitutively expressed genes encoding organellar proteins. Furthermore, it appears that AtWRKY40 and AtWRKY63 are particularly involved in regulating the expression of genes responding commonly to both mitochondrial and chloroplast dysfunction but not of genes responding to either mitochondrial or chloroplast perturbation. In conclusion, this study establishes the role of WRKY transcription factors in the coordination of stress-responsive genes encoding mitochondrial and chloroplast proteins.

The perception and integration of stress stimuli with that of mitochondrion function are important during periods of perturbed cellular homeostasis. In a continuous effort to delineate these mitochondrial/stress-interacting networks, forward genetic screens using the mitochondrial stress response marker alternative oxidase 1a (AOX1a) provide a useful molecular tool to identify and characterize regulators of mitochondrial stress signaling (referred to as regulators of alternative oxidase 1a [RAOs] components). In this study, we reveal that mutations in genes coding for proteins associated with auxin transport and distribution resulted in a greater induction of AOX1a in terms of magnitude and longevity. Three independent mutants for polarized auxin transport, rao3/big, rao4/pin-formed1, and rao5/multidrug-resistance1/abcb19, as well as the Myb transcription factor rao6/asymmetric leaves1 (that displays altered auxin patterns) were identified and resulted in an acute sensitivity toward mitochondrial dysfunction.

The composition of the mitochondrial outer membrane is notoriously difficult to deduce by orthology to other organisms, and biochemical enrichments are inevitably contaminated with the closely associated inner mitochondrial membrane and endoplasmic reticulum. In order to identify novel proteins of the outer mitochondrial membrane in Arabidopsis (Arabidopsis thaliana), we integrated a quantitative mass spectrometry analysis of highly enriched and prefractionated samples with a number of confirmatory biochemical and cell biology approaches. This approach identified 42 proteins, 27 of which were novel, more than doubling the number of confirmed outer membrane proteins in plant mitochondria and suggesting novel functions for the plant outer mitochondrial membrane. The novel components identified included proteins that affected mitochondrial morphology and/or segregation, a protein that suggests the presence of bacterial type lipid A in the outer membrane, highly stress-inducible proteins, as well as proteins necessary for embryo development and several of unknown function. Additionally, proteins previously inferred via orthology to be present in other compartments, such as an NADH: cytochrome B5 reductase required for hydroxyl fatty acid accumulation in developing seeds, were shown to be located in the outer membrane. These results also revealed novel proteins, which may have evolved to fulfill plant-specific requirements of the mitochondrial outer membrane, and provide a basis for the future functional characterization of these proteins in the context of mitochondrial intracellular interaction.

Bacterial adhesion and biofilm formation are ubiquitous undesirable phenomena in the marine industry and the medical industry, usually causing economic losses and serious health problems. Numerous efforts have been made to reduce bacterial adhesion and subsequent biofilm formation, most of which are based on the release of toxic biocides from coatings or substrates. In recent years, surface topography has been found to substantially influence the interaction between bacteria and surfaces. This review summarizes previous work dedicated in searching for the relationship between bacterial adhesion and surface topography in the last eight years, as well as the proposed mechanisms by which surface topographic features interact with bacterial cells. Next, various natural and artificial surfaces with bactericidal surface topography along with their bactericidal mechanisms and efficiency are introduced. Finally, the technologies for constructing antibacterial surfaces are briefly summarized.

A short root mutant was isolated from an EMS-generated rice mutant library. Under normal growth conditions, the mutant exhibited short root, delayed flowering, and partial sterility. Some sections of the roots revealed that the cell length along the longitudinal axis was reduced and the cell shape in the root elongation zone shrank. Genetic analysis indicated that the short root phenotype was controlled by a recessive gene. Map-based cloning revealed that a nucleotide substitution causing an amino acid change from Gly to Arg occurred in the predicted rice gene (Os02g0550600). It coded an alkaline/neutral invertase and was homologous to Arabidopsis gene AtCyt-inv1. This gene was designated as OsCyt-inv1. The results of carbohydrate analysis showed an accumulation of sucrose and reduction of hexose in the Oscyt-inv1 mutant. Exogenously supplying glucose could rescue the root growth defects of the Oscyt-inv1 mutant. These results indicated that OsCyt-inv1 played important roles in root cell development and reproductivity in rice.

SUMMARYOne of the most stress-responsive genes encoding a mitochondrial protein in Arabidopsis (At3g50930) has been annotated as AtBCS1 (cytochrome bc1 synthase 1), but was previously functionally uncharacterised. Here, we show that the protein encoded by At3g50930 is present as a homo-multimeric protein complex on the outer mitochondrial membrane and lacks the BCS1 domain present in yeast and mammalian BCS1 proteins, with the sequence similarity restricted to the AAA ATPase domain. Thus we propose to re-annotate this protein as AtOM66 (Outer Mitochondrial membrane protein of 66 kDa). While transgenic plants with reduced AtOM66 expression appear to be phenotypically normal, AtOM66 over-expression lines have a distinct phenotype, showing strong leaf curling and reduced starch content. Analysis of mitochondrial protein content demonstrated no detectable changes in mitochondrial respiratory complex protein abundance. Consistent with the stress inducible expression pattern, over-expression lines of AtOM66 are more tolerant to drought stress but undergo stress-induced senescence earlier than wild type. Genome-wide expression analysis revealed a constitutive induction of salicylic acid-related (SA) pathogen defence and cell death genes in over-expression lines. Conversely, expression of SA marker gene PR-1 was reduced in atom66 plants, while jasmonic acid response genes PDF1.2 and VSP2 have increased transcript abundance. In agreement with the expression profile, AtOM66 over-expression plants show increased SA content, accelerated cell death rates and are more tolerant to the biotrophic pathogen Pseudomonas syringae, but more susceptible to the necrotrophic fungus Botrytis cinerea. In conclusion, our results demonstrate a role for AtOM66 in cell death and amplifying SA signalling.