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  1. Free, publicly-accessible full text available February 15, 2025
  2. Abstract

    Heat shock protein 101 (HSP101) in plants, and bacterial and yeast orthologs, is essential for thermotolerance. To investigate thermotolerance mechanisms involving HSP101, we performed a suppressor screen in Arabidopsis thaliana of a missense HSP101 allele (hot1–4). hot1–4 plants are sensitive to acclimation heat treatments that are otherwise permissive for HSP101 null mutants, indicating that the hot1–4 protein is toxic. We report one suppressor (shot2, suppressor of hot1–4 2) has a missense mutation of a conserved residue in CLEAVAGE STIMULATION FACTOR77 (CstF77), a subunit of the polyadenylation complex critical for mRNA 3′ end maturation. We performed ribosomal RNA depletion RNA-Seq and captured transcriptional readthrough with a custom bioinformatics pipeline. Acclimation heat treatment caused transcriptional readthrough in hot1–4 shot2, with more readthrough in heat-induced genes, reducing the levels of toxic hot1–4 protein and suppressing hot1–4 heat sensitivity. Although shot2 mutants develop like the wild type in the absence of stress and survive mild heat stress, reduction of heat-induced genes and decreased HSP accumulation makes shot2 in HSP101 null and wild-type backgrounds sensitive to severe heat stress. Our study reveals the critical function of CstF77 for 3′ end formation of mRNA and the dominant role of HSP101 in dictating the outcome of severe heat stress.

     
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  3. Summary

    As rapid changes in climate threaten global crop yields, an understanding of plant heat stress tolerance is increasingly relevant. Heat stress tolerance involves the coordinated action of many cellular processes and is particularly energy demanding. We acquired a knockout mutant and generated knockdown lines inArabidopsis thalianaof the d subunit of mitochondrial ATP synthase (gene name:ATPQ, AT3G52300, referred to hereafter asATPd), a subunit of the peripheral stalk, and used these to investigate the phenotypic significance of this subunit in normal growth and heat stress tolerance. Homozygous knockout mutants forATPdcould not be obtained due to gametophytic defects, while heterozygotes possess no visible phenotype. Therefore, we used RNA interference to create knockdown plant lines for further studies. Proteomic analysis and blue native gels revealed thatATPddownregulation impairs only subunits of the mitochondrial ATP synthase (complex V). Knockdown plants were more sensitive to heat stress, had abnormal leaf morphology, and were severely slow growing compared to wild type. These results indicate that ATPd plays a crucial role in proper function of the mitochondrial ATP synthase holoenzyme, which, when reduced, leads to wide‐ranging defects in energy‐demanding cellular processes. In knockdown plants, more hydrogen peroxide accumulated and mitochondrial dysfunction stimulon (MDS) genes were activated. These data establish the essential structural role of ATPd and support the importance of complex V in normal plant growth, and provide new information about its requirement for heat stress tolerance.

     
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  4. Summary

    Mitochondria play critical roles in generating ATP through oxidative phosphorylation (OXPHOS) and produce both damaging and signaling reactive oxygen species (ROS). They have reduced genomes that encode essential subunits of the OXPHOS machinery. Mitochondrial Transcription tERmination Factor‐related (mTERF) proteins are involved in organelle gene expression, interacting with organellar DNA or RNA.

    We previously found that mutations inArabidopsis thaliana mTERF18/SHOT1enable plants to better tolerate heat and oxidative stresses, presumably due to low ROS production and reduced oxidative damage.

    Here we discover thatshot1mutants have greatly reduced OXPHOS complexes I and IV and reveal that suppressor ofhot1‐41 (SHOT1) binds DNA and localizes to mitochondrial nucleoids, which are disrupted inshot1. Furthermore, three homologues of animal ATPase family AAA domain‐containing protein 3 (ATAD3), which is involved in mitochondrial nucleoid organization, were identified as SHOT1‐interacting proteins. Importantly, disrupting ATAD3 function disrupts nucleoids, reduces accumulation of complex I, and enhances heat tolerance, as is seen inshot1mutants.

    Our data link nucleoid organization to OXPHOS biogenesis and suggest that the common defects inshot1mutants and ATAD3‐disrupted plants lead to critical changes in mitochondrial metabolism and signaling that result in plant heat tolerance.

     
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