Inactivation of Mitochondrial Complex Ⅰ Induces the Expression of a Twin Cysteine Protein that Targets and Affects Cytosolic, Chloroplastidic and Mitochondrial Function

At12Cys-1 （At5g64400） and At12Cys-2 （At5g09570） are two closely related isogenes that encode small, twin cysteine proteins, typically located in mitochondria. At12Cys-2 transcript is induced in a variety of mutants with disrupted mitochondrial proteins, but an increase in At12Cys protein is only detected in mutants with reduced mitochondrial complex I abundance. Induction of At12Cys protein in mutants that lack mitochondrial complex I is accompanied by At12Cys protein located in mitochondria, chloroplasts, and the cytosoh Biochemical analyses revealed that even single gene deletions, i.e., At12cys-1 orAtl2cys-2, have an effect on mitochondrial and chloroplast functions. However, only double mutants, i.e., At12cys-1：At12cys.2, affect the abundance of protein and mRNA transcripts encoding translation elongation factors as well as rRNA abundance. Blue native PAGE showed that At12Cys co-migrated with mitochondrial supercomplex I ＋ lU. Likewise, deletion of both At12cys-1 and At12cys-2 genes, but not single gene deletions, results in enhanced tolerance to drought and light stress and increased anti-oxidant capacity. The induction and multiple localization of At12Cys upon a reduction in complex I abundance provides a mechanism to specifically signal mitochondrial dysfunction to the cytosol and then beyond to other organelles in the cell.

scCloudMine:A cloud-based app for visualization,comparison,and exploration of single-cell transcriptomic data

scCloudMine is a cloud-based application for visualization,comparison,and exploration of single-cell transcriptome data.It does not require an on-site,high-power computing server,installation,or associated expertise and expense.Users upload their own or publicly available scRNA-seq datasets after preprocessing for visualization using a web browser.The data can be viewed in two color modes—Cluster,representing cell identity,and Values,showing levels of expression—and data can be queried using keywords or gene identification number(s).Using the app to compare studies,we determined that some genes frequently used as cell-type markers are in fact study specific.The apparent cell-specific expression of PHO1;H3 differed between GFP-tagging and scRNA-seq studies.Some phosphate transporter genes were induced by protoplasting,but they retained cell specificity,suggesting that cell-specific responses to stress(i.e.,protoplasting)can occur.Examination of the cell specificity of hormone response genes revealed that 132 hormone-responsive genes display restricted expression and that the jasmonate response gene TIFY8 is expressed in endodermal cells,in contrast to previous reports.It also appears that JAZ repressors have cell-type-specific functions.These features identified using scCloudMine highlight the need for resources to enable biological researchers to compare their datasets of interest under a variety of parameters.scCloudMine enables researchers to form new hypotheses and perform comparative studies and allows for the easy re-use of data from this emerging technology by a wide variety of users who may not have access or funding for high-performance on-site computing and support.

Co-regulation of mitochondrial and chloroplast function: Molecular components and mechanisms

The metabolic interdependence,interactions,and coordination of functions between chloroplasts and mitochondria are established and intensively studied.However,less is known about the regulatory components that control these interactions and their responses to external stimuli.Here,we outline how chloroplastic and mitochondrial activities are coordinated via common components involved in signal transduction pathways,gene regulatory events,and post-transcriptional processes.The endoplasmic reticulum emerges as a point of convergence for both transcriptional and post-transcriptional pathways that coordinate chloroplast and mitochondrial functions.Although the identification of molecular components and mechanisms of chloroplast and mitochondrial signaling increasingly suggests common players,this raises the question of how these allow for distinct organelle-specific downstream pathways.Outstanding questions with respect to the regulation of post-transcriptional pathways and the cell and/or tissue specificity of organelle signaling are crucial for understanding how these pathways are integrated at a wholeplant level to optimize plant growth and its response to changing environmental conditions.

Coordinated regulation of the mitochondrial retrograde response by circadian clock regulators and ANAC017

Mitochondrial retrograde signaling(MRS)supports photosynthetic function under a variety of conditions.Induction of mitochondrial dysfunction with myxothiazol(a specific inhibitor of the mitochondrial bc1 complex)or antimycin A(an inhibitor of the mitochondrial bc1 complex and cyclic electron transport in the chloroplast under light conditions)in the light and dark revealed diurnal control of MRS.This was evidenced by(1)significantly enhanced binding of ANAC017 to promoters in the light compared with the dark in Arabidopsis plants treated with myxothiazol(but not antimycin A),(2)overlap in the experimentally determined binding sites for ANAC017 and circadian clock regulators in the promoters of ANAC013 and AOX1a,(3)a diurnal expression pattern for ANAC017 and transcription factors it regulates,(4)altered expression of ANAC017-regulated genes in circadian clock mutants with and without myxothiazol treatment,and(5)a decrease in the magnitude of LHY and CCA1 expression in an ANAC017-overexpressing line and protein–protein interaction between ANAC017 and PIF4.This study also shows a large difference in transcriptome responses to antimycin A and myxothiazol in the dark:these responses are ANAC017 independent,observed in shoots and roots,similar to biotic challenge and salicylic acid responses,and involve ERF and ZAT transcription factors.This suggests that antimycin A treatment stimulates a second MRS pathway that is mediated or converges with salicylic acid signaling and provides a merging point with chloroplast retrograde signaling.