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HsfA2 controls the activity of developmentally and stress-regulated heat stress protection mechanisms in tomato male reproductive tissues

ABSTRACT: Male reproductive tissues are more sensitive to heat stress compared to vegetative tissues, however the basis of this phenomenon is poorly understood. Heat stress transcription factors (Hsfs) regulate the transcriptional changes required for protection and recovery from heat stress. HsfA2 has been characterized as co-activator of HsfA1a in tomato and is considered as one of the major Hsfs accumulating in response to elevated temperatures. The role of HsfA2 in heat stress response of different tissues was examined by exploring the composition and structure of the tissue-specific regulatory networks in transgenic tomato plants with suppressed HsfA2 expression (A2AS). Transcriptome analysis revealed that HsfA2 acts in condition- and tissue-specific manner and that only a subset of heat stress induced genes require HsfA2 for higher expression. Remarkably, although HsfA2 is not essential for thermotolerance in seedlings and flowering plants, it is required for maintenance pollen viability under stress conditions. We show that the activation of Hsf networks is important for the developmentally regulated priming of heat stress response occurring at early stages of anther and pollen development. Thereby, HsfA2 is involved in pollen thermotolerance by directly regulating heat stress responsive genes but also by stimulating the synthesis of molecular chaperones under non-stress conditions.

ORGANISM(S): Solanum lycopersicum

PROVIDER: GSE68500 | GEO | 2016/02/22

SECONDARY ACCESSION(S): PRJNA282940

REPOSITORIES: GEO

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Project description:The expression of heat-shock proteins (Hsps) induced by a non-lethal heat treatment confers acquired thermotolerance (AT) to organisms against a subsequent challenge of otherwise lethal temperature. After stress signal lifted, AT gradually decayed with the decline of Hsps during recovery period. The duration of AT may be critical for sessile organisms, such as plants, to survive repeated heat stress in the environment. To identify heat-induced genes involved in duration of AT, we took a reverse-genetics approach by screening for Arabidopsis T-DNA insertion mutants that show decreased thermotolerance after a long recovery at non-stress condition following a conditioning treatment. Among the tested mutants corresponding to 47 genes, only the HsfA2 knockout mutant showed significant phenotype. The mutant plants were more sensitive to severe heat stress than the wild type after long but not short recovery following a pretreatment at 37oC, which can be complemented by introducing a wild-type copy of the gene. Quantitative hypocotyl elongation assay also revealed that AT decayed faster in the absence of HsfA2. Significant decline of the transcript levels of several highly heat-induced genes was observed in the HsfA2 knockout plants after a 4-h recovery or after 2 h of prolonged heat stress. Immunoblot anlysis showed that Hsa32 and class I small Hsp were lower in the mutant than in the wild type after a long recovery. Our results suggest that HsfA2 as a heat-induced transactivator sustains the post-stress expression of Hsp genes and extends the duration of AT in Arabidopsis. Experiment Overall Design: Total RNA was isolated from the seedlings of 5-d old wild-type and HsfA2 knockout mutant seedlings (a pool of about 100 plants per treatment in duplicates) harvested immediately after heat shock treatment. In this experiment, total 12 chips were used, 1 each for 2 biological replicates of the control and HS-treated samples for the wild type and mutant plants.

Project description:Heat stress is a major cause for yield loss in many crops, including vegetable crops. Even short waves of high temperature, becoming more frequent during recent years, can be detrimental. Pollen development is most heat-sensitive, being the main cause for reduced productivity under heat-stress across a wide range of crops. The molecular mechanisms involved in pollen heat-stress response and thermotolerance are however not fully understood. Recently, we have demonstrated that ethylene, a gaseous plant hormone, plays a role in tomato (Solanum lycopersicum) pollen thermotolerance. These results were substantiated in the current work showing that increasing ethylene levels by using an ethylene-releasing substance, ethephon, prior to heat-stress exposure, increased pollen quality. A proteomic approach was undertaken, to unravel the mechanisms underlying pollen heat-stress response and ethylene-mediated pollen thermotolerance in developing pollen grains. Proteins were extracted and analyzed by means of a gel LC-MS fractionation protocol, and a total of 1355 proteins were identified. A dataset of 721 proteins, detected in three biological replicates of at least one of the applied treatments, was used for all analyses. Quantitative analysis was performed based on peptide count. The analysis revealed that heat-stress affected the developmental program of pollen, including protein homeostasis (components of the translational and degradation machinery), carbohydrate and energy metabolism. Ethephon-pretreatment shifted the heat-stressed pollen proteome closer to the proteome under non-stressful conditions, namely, by showing higher abundance of proteins involved in protein synthesis, degradation, tricarboxylic acid cycle and RNA regulation. Furthermore, up-regulation of protective mechanisms against oxidative stress was observed following ethephon-treatment (including higher abundance of glutathione-disulfide reductase, glutaredoxin and protein disulfide isomerase). Taken together, the findings identified systemic and fundamental components of pollen thermotolerance, and serve as a valuable quantitative protein database for further research.

Project description:Global temperature increase poses a serious challenge for agricultural production worldwide, affecting yield in many crops including vegetable crops. While most crop plants can survive temperature increases during their vegetative growth periods, the reproduction phase is highly heat-stress (HS)-sensitive. Impaired pollen development and functioning under HS is implicated as the major cause for yield reduction. To better understand HS effect on pollen and identify pollen thermotolerance mechanisms, we established conditions that enable developing pollen grains to acquire thermotolerance (ATT conditions), using tomato as a model system. High-throughput sequencing at cDNA level was performed by Massive Analysis of 3’cDNA using Illumina HiSeq 2000 technology, generating a total of 6430 and 4660 transcripts differentially expressed (p ≤ 1e-05) during pollen development/maturation and following response of developing pollen to ATT, respectively. Gene Onthology functional analysis showed that transcripts related to maintenance of protein homeostasis (translation, proteolysis, protein folding) were enriched during pollen maturation and following the ATT treatment in our study, highlighting these processes as central for enabling pollen maturation and maintenance of pollen functioning under HS. The transcriptomic data was compared to available pollen proteomic data based on the same experimental setup and an overlap of 47% was detected between differentially expressed proteins and transcripts following ATT conditions, highlighting genes/proteins involved in protein folding, oxidation-reduction and translation, and validating transcriptomic results. Involvement of mitochondria and endoplasmic reticulum in pollen heat acclimation, and activation of several HSPs including sHSPs and HSP101, for protecting pollen cellular components including the translational machinery, are indicated. The results of this study can serve as a valuable resource of genes for future research on improving pollen thermotolerance.

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HsfA2 controls the activity of developmentally and stress-regulated heat stress protection mechanisms in tomato male reproductive tissues

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