Repeated sprint training in hypoxia induces specific skeletal muscle adaptations through S100A protein signaling

Athletes increasingly engage in repeated sprint training consisting in repeated short all-out efforts interspersed by short recoveries. When performed in hypoxia (RSH), it may lead to greater training effects than in normoxia (RSN); however, the underlying molecular mechanisms remain unclear. This study aimed at elucidating the effects of RSH on skeletal muscle metabolic adaptations as compared to RSN. Sixteen healthy young men performed nine repeated sprint training sessions in either normoxia (FIO2 = 0.209, RSN, n = 7) or normobaric hypoxia (FIO2 = 0.136, RSH, n = 9). Before and after the training period, exercise performance was assessed by using repeated sprint ability (RSA) and Wingate tests. Vastus lateralis muscle biopsies were performed to investigate muscle metabolic adaptations using proteomics combined with western blot analysis. Similar improvements were observed in RSA and Wingate tests in both RSN and RSH groups. At the muscle level, RSN and RSH reduced oxidative phosphorylation protein content but triggered an increase in mitochondrial biogenesis proteins. Proteomics showed an increase in several S100A family proteins in the RSH group, among which S100A13 most strongly. We confirmed a significant increase in S100A13 protein by western blot in RSH, which was associated with increased Akt phosphorylation and its downstream targets regulating protein synthesis. Altogether our data indicate that RSH may activate an S100A/Akt pathway to trigger specific adaptations as compared to RSN.

Effects of a 6-Week Repeated-Sprint Training With Voluntary Hypoventilation at Low and High Lung Volume on Repeated-Sprint Ability in Female Soccer Players

PURPOSE

To investigate the effects of repeated-sprint training with voluntary hypoventilation at low (RSH-VHL) and high (RS-VHH) lung volume on repeated-sprint ability (RSA) in female athletes.

METHODS

Over a 6-week period, 24 female soccer players completed 12 sessions of repeated 30-m running sprints with end-expiratory breath holding (RSH-VHL, n = 8), end-inspiratory breath holding (RS-VHH, n = 8), or unrestricted breathing (RS-URB, n = 8). Before and after training, a running RSA test consisting of performing 30-m all-out sprints until exhaustion was implemented.

RESULTS

From before to after training, the number of sprints completed during the RSA test was increased in both RSH-VHL (19.3 [0.9] vs 22.6 [0.9]; P < .01) and RS-VHH (19.3 [1.5] vs 20.5 [1.7]; P < .01) but not in RS-URB (19.4 [1.3] vs 19.5 [1.7]; P = .67). The mean velocity and the percentage decrement score calculated over sprints 1 to 17 were, respectively, higher (82.2% [1.8%] vs 84.6% [2.1%] of maximal velocity) and lower (23.7% [3.1%] vs 19.4% [3.2%]) in RSH-VHL (P < .01), whereas they remained unchanged in RS-VHH and RS-URB. The mean arterial oxygen saturation recorded during training at the end of the sprints was lower in RSH-VHL (92.1% [0.4%]) than in RS-VHH (97.3% [0.1%]) and RS-URB (97.8% [0.1%]).

CONCLUSIONS

This study shows that female athletes can benefit from the RSH-VHL intervention to improve RSA. The performance gains may have been limited by the short sprinting distance with end-expiratory breath holding, which provoked only moderate hypoxemia. The increase in the number of sprints in RS-VHH seems to show that factors other than hypoxia may have played a role in RSA improvement.

Trichoderma viride Colonizes the Roots of Brassica napus L., Alters the Expression of Stress-Responsive Genes, and Increases the Yield of Canola under Field Conditions during Drought

In this work, we present the results of the inoculation of canola seeds (Brassica napus L.) with Trichoderma viride strains that promote the growth of plants. Seven morphologically different strains of T. viride (TvI-VII) were shown to be capable of synthesizing auxins and exhibited cellulolytic and pectinolytic activities. To gain a deeper insight into the molecular mechanisms underlying canola-T. viride interactions, we analyzed the canola stress genes metallothioneins (BnMT1-3) and stringent response genes (BnRSH1-3 and BnCRSH). We demonstrated the presence of cis-regulatory elements responsive to fungal elicitors in the promoter regions of B. napus MT and RSH genes and observed changes in the levels of the transcripts of the above-mentioned genes in response to root colonization by the tested fungal strains. Of the seven tested strains, under laboratory conditions, T. viride VII stimulated the formation of roots and the growth of canola seedlings to the greatest extent. An experiment conducted under field conditions during drought showed that the inoculation of canola seeds with a suspension of T. viride VII spores increased yield by 16.7%. There was also a positive effect of the fungus on the height and branching of the plants, the number of siliques, and the mass of a thousand seeds. We suggest that the T. viride strain TvVII can be used in modern sustainable agriculture as a bioinoculant and seed coating to protect B. napus from drought.

Anaerobic RSH-dependent tellurite reduction contributes to Escherichia coli tolerance against tellurite

BACKGROUND

Tellurium is a rare metalloid that exerts high toxicity on cells, especially on bacteria, partly due to reactive oxygen species (ROS) generation. Moreover, it has also been observed that tellurite can target free cell thiols groups (RSH) (i.e. reduced glutathione (GSH)), enhancing the cellular redox imbalance. Additionally, in vitro experiments have suggested that several enzymes can reduce tellurite (IV) to its elemental form (0); where RSH present on their active sites may be responsible for the process. Nevertheless, the mechanisms implemented by bacteria for tellurite reduction and its role in resistance have not been evaluated in vivo.

RESULTS

This work shows that tellurite reduction to elemental tellurium is increased under anaerobic conditions in E. coli cells. The in vivo tellurite reduction is related to the intracellular concentration of total RSH, in the presence and absence of oxygen. This metabolization of tellurite directly contributes to the resistance of the bacteria to the oxyanion.

CONCLUSIONS

We demonstrated that in vivo tellurite reduction is related to the intracellular thiol concentration, i.e. large availability of cellular RSH groups, results in a more significant reduction of tellurite. Furthermore, we observed that, when the bacterium exhibits less resistance to the oxyanion, a decreased tellurite reduction was seen, affecting the growth fitness. Together, these results let us propose that tellurite reduction and the intracellular RSH content are related to the oxyanion bacterial resistance, this tripartite mechanism in an oxygen-independent anaerobic process.

Repeated sprint exercise in hypoxia stimulates HIF-1-dependent gene expression in skeletal muscle

PURPOSE

Our aim was to determine the effect of repeated sprint exercise in hypoxia on HIF-1 and HIF-1-regulated genes involved in glycolysis, mitochondrial turnover and oxygen transport. We also determined whether genes upregulated by exercise in hypoxia were dependent on the activation of HIF-1 in an in vitro model of exercise in hypoxia.

METHODS

Eight endurance athletes performed bouts of repeated sprint exercise in control and hypoxic conditions. Skeletal muscle was sampled pre, post and 3 h post-exercise. HIF-1α protein and HIF1A, PDK1, GLUT4, VEGFA, BNIP3, PINK1 and PGC1A mRNA were measured. C2C12 myotubes were exposed to hypoxia and muscle contraction following treatment with a HIF-1α inhibitor to determine whether hypoxia-sensitive gene expression was dependent on HIF-1α.

RESULTS

Sprint exercise in hypoxia increased HIF-1α protein expression immediately post-exercise [fold change (FC) = 3.5 ± 2.0]. Gene expression of PDK1 (FC = 2.1 ± 1.2), BNIP3 (FC = 2.4 ± 1.4) and VEGFA (FC = 2.7 ± 1.7) increased 3 h post-exercise in hypoxia but not control. PGC1A mRNA increased 3 h post-exercise in control (FC = 5.16) and hypoxia (FC = 5.7 ± 4.1) but there was no difference between the trials. Results from the in vitro experiment showed that hypoxia plus contraction also increased PDK1, BNIP3, and VEGFA gene expression. These responses were inhibited when HIF-1 protein activity was suppressed.

CONCLUSION

Repeated sprint exercise in hypoxia upregulates some genes involved in glycolytic metabolism, mitochondrial turnover, and oxygen transport. HIF-1α is necessary for the expression of these genes in skeletal muscle cells.

In Silico Study of the RSH (RelA/SpoT Homologs) Gene Family and Expression Analysis in Response to PGPR Bacteria and Salinity in Brassica napus

Among several mechanisms involved in the plant stress response, synthesis of guanosine tetra and pentaphosphates (alarmones), homologous to the bacterial stringent response, is of crucial importance. Plant alarmones affect, among others, photosynthetic activity, metabolite accumulation, and nutrient remobilization, and thus regulate plant growth and development. The plant RSH (RelA/SpoT homolog) genes, that encode synthetases and/or hydrolases of alarmones, have been characterized in a limited number of plant species, e.g., Arabidopsis thaliana, Oryza sativa, and Ipomoea nil. Here, we used dry-to-wet laboratory research approaches to characterize RSH family genes in the polyploid plant Brassica napus. There are 12 RSH genes in the genome of rapeseed that belong to four types of RSH genes: 6 RSH1, 2 RSH2, 3 RSH3, and 1 CRSH. BnRSH genes contain 13-24 introns in RSH1, 2-6 introns in RSH2, 1-6 introns in RSH3, and 2-3 introns in the CRSH genes. In the promoter regions of the RSH genes, we showed the presence of regulatory elements of the response to light, plant hormones, plant development, and abiotic and biotic stresses. The wet-lab analysis showed that expression of BnRSH genes is generally not significantly affected by salt stress, but that the presence of PGPR bacteria, mostly of Serratia sp., increased the expression of BnRSH significantly. The obtained results show that BnRSH genes are differently affected by biotic and abiotic factors, which indicates their different functions in plants.

Estimates of RelSeq, Mesh1, and SAHMex Hydrolysis of (p)ppGpp and (p)ppApp by Thin Layer Chromatography and NADP/NADH Coupled Assays

The Mesh1 class of hydrolases found in bacteria, metazoans and humans was discovered as able to cleave an intact pyrophosphate residue esterified on the 3'hydroxyl of (p)ppGpp in a Mn²⁺ dependent reaction. Here, thin layer chromatography (TLC) qualitative evidence is presented indicating the substrate specificity of Mesh1 from Drosophila melanogaster and human MESH1 also extends to the (p)ppApp purine analogs. More importantly, we developed real time enzymatic assays, coupling ppNpp hydrolysis to NADH oxidation and pppNpp hydrolysis to NADP⁺ reduction, which facilitate estimation of kinetic constants. Furthermore, by using this assay technique we confirmed TLC observations and also revealed that purified small alarmone hydrolase (SAH_Mex) from Methylobacterium extorquens displays a strong hydrolase activity toward (p)ppApp but only negligible activity toward (p)ppGpp. In contrast, the substrate specificity of the hydrolase present in catalytically active N-terminal domain of the RSH protein from Streptococcus equisimilis (Rel_Seq) includes (p)ppGpp but not (p)ppApp. It is noteworthy that the RSH protein from M. extorquens (RSH_Mex) has been recently shown to synthesize both (p)ppApp and (p)ppGpp.

Effects of High-Intensity Interval Training in Hypoxia on Taekwondo Performance

PURPOSE

To evaluate the effects of a 6-week taekwondo-specific high-intensity interval training (HIIT) in simulated normobaric hypoxia on physical fitness and performance in taekwondoists.

METHODS

Eighteen male and female black-belt taekwondoists trained twice a week for 6 weeks in normoxia or in hypoxia (FiO2 = 0.143 O2). The HIIT was composed of specific taekwondo movements and simulated fights. Body composition analyses and a frequency speed of kick test during 10 seconds (FSKT10s) and 5 × 10 seconds (FSKTmult), countermovement jump (CMJ) test, Wingate test, and an incremental treadmill test were performed before and after training. Blood lactate concentrations were measured after the FSKTmult and Wingate tests, and a fatigue index during the tests was calculated.

RESULTS

A training effect was found for FSKT10s (+35%, P < .001), FSKTmult (+32%, P < .001), and fatigue index (-48%, P = .002). A training effect was found for CMJ height (+5%, P = .003) during the CMJ test. After training, CMJ height increased in hypoxia only (+7%, P = .005). No effect was found for the parameters measured during Wingate test. For the incremental treadmill test, a training effect was found for peak oxygen consumption (P = .002), the latter being 10% lower after than before training in normoxia only (P = .002).

CONCLUSIONS

In black-belt taekwondoists, hypoxic HIIT twice a week for 6 weeks provides tiny additional gains on key performance parameters compared with normoxic HIIT. Whether the trivial effects reported here might be of physiological relevance to improve performance remains debatable and should be tested individually.

Triggering the stringent response: signals responsible for activating (p)ppGpp synthesis in bacteria

The stringent response is a conserved bacterial stress response mechanism that allows bacteria to respond to nutritional challenges. It is mediated by the alarmones pppGpp and ppGpp, nucleotides that are synthesized and hydrolyzed by members of the RSH superfamily. Whilst there are key differences in the binding targets for (p)ppGpp between Gram-negative and Gram-positive bacterial species, the transient accumulation of (p)ppGpp caused by nutritional stresses results in a global change in gene expression in all species. The RSH superfamily of enzymes is ubiquitous throughout the bacterial kingdom, and can be split into three main groups: the long-RSH enzymes; the small alarmone synthetases (SAS); and the small alarmone hydrolases (SAH). Despite the prevalence of these enzymes, there are important differences in the way in which they are regulated on a transcriptional and post-translational level. Here we provide an overview of the diverse regulatory mechanisms that are involved in governing this crucial signalling network. Understanding how the RSH superfamily members are regulated gives insights into the varied important biological roles for this signalling pathway across the bacteria.

Intramolecular Interactions Dominate the Autoregulation of Escherichia coli Stringent Factor RelA

Amino acid starvation in Escherichia coli activates the enzymatic activity of the stringent factor RelA, leading to accumulation of the alarmone nucleotide (p)ppGpp. The alarmone acts as an intercellular messenger to regulate transcription, translation and metabolism to mediate bacterial stress adaptation. The enzymatic activity of RelA is subject to multi-layered allosteric control executed both by ligands - such as "starved" ribosomal complexes, deacylated tRNA and pppGpp - and by individual RelA domains. The auto-regulation of RelA is proposed to act either in cis (inhibition of the enzymatic activity of the N-terminal region, NTD, by regulatory C-terminal region, CTD) or in trans (CTD-mediated dimerization leading to enzyme inhibition). In this report, we probed the regulatory roles of the individual domains of E. coli RelA and our results are not indicative of RelA dimerization being the key regulatory mechanism. First, at growth-permitting levels, ectopic expression of RelA CTD does not interfere with activation of native RelA, indicating lack of regulation via inhibitory complex formation in the cell. Second, in our biochemical assays, increasing RelA concentration does not decrease the enzyme activity, as would be expected in the case of efficient auto-inhibition via dimerization. Third, while high-level CTD expression efficiently inhibits the growth, the effect is independent of native RelA and is mediated by direct inhibition of protein synthesis, likely via direct interaction with the ribosomal A-site. Finally, deletion of the RRM domain of the CTD region leads to growth inhibition mediated by accumulation of (p)ppGpp, suggesting de-regulation of the synthetic activity in this mutant.

Make and break the alarmone: regulation of (p)ppGpp synthetase/hydrolase enzymes in bacteria

Bacteria use dedicated mechanisms to respond adequately to fluctuating environments and to optimize their chances of survival in harsh conditions. One of the major stress responses used by virtually all bacteria relies on the sharp accumulation of an alarmone, the guanosine penta- or tetra-phosphate commonly referred to as (p)ppGpp. Under stressful conditions, essentially nutrient starvation, these second messengers completely reshape the metabolism and physiology by coordinately modulating growth, transcription, translation and cell cycle. As a central regulator of bacterial stress response, the alarmone is also involved in biofilm formation, virulence, antibiotics tolerance and resistance in many pathogenic bacteria. Intracellular concentrations of (p)ppGpp are determined by a highly conserved and widely distributed family of proteins called RelA-SpoT Homologs (RSH). Recently, several studies uncovering mechanisms that regulate RSH activities have renewed a strong interest in this field. In this review, we outline the diversity of the RSH protein family as well as the molecular devices used by bacteria to integrate and transform environmental cues into intracellular (p)ppGpp levels.

Repeated Treadmill Sprints Impair Cognitive Performance in Amateur Team-Sport Athletes When Performed in Normobaric Hypoxia

This study determined if a single bout of repeated-sprint running under hypoxic (RSH) conditions was associated with impaired cognitive function when compared with repeated-sprint running under normoxic (RSN) conditions. Eleven amateur team-sport athletes performed a repeated-sprint running protocol (4 sets of 4, 4-s all-out sprints; i.e., RSR₄₄₄) under both conditions (14.5% and 20.9% O₂) on a non-motorized treadmill. Changes in S_pO₂, pre-frontal cortex total haemoglobin (Δ[THb]), oxyhaemoglobin (Δ[O₂Hb]), deoxyhaemoglobin (Δ[HHb]) and cognitive function (detection task: DET; identification task: IDN; one card learning task: OCL; performed pre and 20 min post RSR₄₄₄) were examined. During RSH, S_pO₂ was lower following each set (p ≤ 0.05), while [HHb] was higher after each set (p ≤ 0.05) compared with RSN. In addition, while there was no effect of condition on DET (p = 0.20) or IDN (p = 0.14), OCL accuracy was lower after, compared with before, RSH (p=0.04), but not RSN (p = 0.52). A significant relationship was observed between Δ[HHB] and ΔOCL accuracy (r = -0.68, p = 0.01). Performance of a single bout of RSH with 14.5% O₂ resulted in impaired cognitive function in amateur team-sport athletes. Coaches should be mindful of timing of RSH prescription with regard to other training sessions that challenge speed and movement accuracy.

Activation of the Stringent Response by Loading of RelA-tRNA Complexes at the Ribosomal A-Site

RelA/SpoT homologs (RSHs) are ubiquitous bacterial enzymes that synthesize and hydrolyze (p)ppGpp in response to environmental challenges. Bacteria cannot survive in hosts and produce infection without activating the (p)ppGpp-mediated stringent response, but it is not yet understood how the enzymatic activities of RSHs are controlled. Using UV crosslinking and deep sequencing, we show that Escherichia coli RelA ((p)ppGpp synthetase I) interacts with uncharged tRNA without being activated. Amino acid starvation leads to loading of cognate tRNA⋅RelA complexes at vacant ribosomal A-sites. In turn, RelA is activated and synthesizes (p)ppGpp. Mutation of a single, conserved residue in RelA simultaneously prevents tRNA binding, ribosome binding, and activation of RelA, showing that all three processes are interdependent. Our results support a model in which (p)ppGpp synthesis occurs by ribosome-bound RelA interacting with the Sarcin-Ricin loop of 23S rRNA.

Small Alarmone Synthetases as novel bacterial RNA-binding proteins

The alarmone nucleotides guanosine pentaphosphate (pppGpp) and tetraphosphate (ppGpp), collectively referred to as (p)ppGpp, are key regulators of bacterial growth, stress adaptation, antibiotic tolerance and pathogenicity. We have recently shown that the Small Alarmone Synthetase (SAS) RelQ from the Gram-positive pathogen Enterococcus faecalis has an RNA-binding activity (Beljantseva et al. 2017). RelQ's activities as an enzyme and as an RNA-binding protein are mutually incompatible: binding of single-stranded RNA potently inhibits (p)ppGpp synthesis in a sequence-specific manner, and RelQ's enzymatic activity destabilizes the RNA:RelQ complex. RelQ's allosteric regulator, pppGpp, destabilizes RNA binding and activates RelQ's enzymatic activity. Since SAS enzymes are widely distributed in bacteria, and, as has been discovered recently, are also mobilized by phages (Dedrick et al. 2017), RNA binding to SASs could be a widespread mechanism. The initial discovery raises numerous questions regarding RNA-binding function of the SAS enzymes: What is the molecular mechanism underlying the incompatibility of RNA:SAS complex formation with pppGpp binding and (p)ppGpp synthesis? What are the RNA targets in living cells? What is the regulatory output of the system - (p)ppGpp synthesis, modulation of RNA structure and function, or both?

Repeated-Sprint Training in Hypoxia Induced by Voluntary Hypoventilation in Swimming

PURPOSE

Repeated-sprint training in hypoxia (RSH) has been shown as an efficient method for improving repeated-sprint ability (RSA) in team-sport players but has not been investigated in swimming. We assessed whether RSH with arterial desaturation induced by voluntary hypoventilation at low lung volume (VHL) could improve RSA to a greater extent than the same training performed under normal breathing (NB) conditions.

METHODS

Sixteen competitive swimmers completed 6 sessions of repeated sprints (2 sets of 16 × 15 m with 30 s send-off) either with VHL (RSH-VHL, n = 8) or with NB (RSN, n = 8). Before and after training, performance was evaluated through an RSA test (25-m all-out sprints with 35 s send-off) until exhaustion.

RESULTS

From before to after training, the number of sprints was significantly increased in RSH-VHL (7.1 ± 2.1 vs 9.6 ± 2.5; P < .01) but not in RSN (8.0 ± 3.1 vs 8.7 ± 3.7; P = .38). Maximal blood lactate concentration ([La]max) was higher after than before in RSH-VHL (11.5 ± 3.9 vs 7.9 ± 3.7 mmol/L; P = .04) but was unchanged in RSN (10.2 ± 2.0 vs 9.0 ± 3.5 mmol/L; P = .34). There was a strong correlation between the increases in the number of sprints and in [La]max in RSH-VHL only (R = .93, P < .01).

CONCLUSIONS

RSH-VHL improved RSA in swimming, probably through enhanced anaerobic glycolysis. This innovative method allows inducing benefits normally associated with hypoxia during swim training in normoxia.

Cytosolic ppGpp accumulation induces retarded plant growth and development

In bacteria a second messenger, guanosine 5'-diphosphate 3'-diphosphate (ppGpp), synthesized upon nutrient starvation, controls many gene expressions and enzyme activities, which is necessary for growth under changeable environments. Recent studies have shown that ppGpp synthase and hydrolase are also conserved in eukaryotes, although their functions are not well understood. We recently showed that ppGpp-overaccumulation in Arabidopsis chloroplasts results in robust growth under nutrient-limited conditions, demonstrating that the bacterial-like stringent response at least functions in plastids. To test if ppGpp also functions in the cytosol, we constructed the transgenic Arabidopsis expressing Bacillus subtilis ppGpp synthase gene yjbM. Upon induction of the gene, the mutant synthesizes ∼10-20-fold higher levels of ppGpp, and its fresh weight was reduced to ˜80% that of the wild type. These results indicate that cytosolic ppGpp negatively regulates plant growth and development.

Arabinosylation Plays a Crucial Role in Extensin Cross-linking In Vitro

Extensins (EXTs) are hydroxyproline-rich glycoproteins (HRGPs) that are structural components of the plant primary cell wall. They are basic proteins and are highly glycosylated with carbohydrate accounting for >50% of their dry weight. Carbohydrate occurs as monogalactosyl serine and arabinosyl hydroxyproline, with arabinosides ranging in size from ~1 to 4 or 5 residues. Proposed functions of EXT arabinosylation include stabilizing the polyproline II helix structure and facilitating EXT cross-linking. Here, the involvement of arabinosylation in EXT cross-linking was investigated by assaying the initial cross-linking rate and degree of cross-linking of partially or fully de-arabinosylated EXTs using an in vitro cross-linking assay followed by gel permeation chromatography. Our results indicate that EXT arabinosylation is required for EXT cross-linking in vitro and the fourth arabinosyl residue in the tetraarabinoside chain, which is uniquely α-linked, may determine the initial cross-linking rate. Our results also confirm the conserved structure of the oligoarabinosides across species, indicating an evolutionary significance for EXT arabinosylation.

Mechanistic investigations in sono-hybrid techniques for rice straw pretreatment

This paper reports comparative study of two chemical techniques (viz. dilute acid/alkali treatment) and two physical techniques (viz. hot water bath and autoclaving) coupled with sonication, termed as sono-hybrid techniques, for hydrolysis of rice straw. The efficacy of each sono-hybrid technique was assessed on the basis of total sugar and reducing sugar release. The system of biomass pretreatment is revealed to be mass transfer controlled. Higher sugar release is obtained during dilute acid treatment than dilute alkali treatment. Autoclaving alone was found to increase sugar release marginally as compared to hot water bath. Sonication of the biomass solution after autoclaving and stirring resulted in significant rise of sugar release, which is attributed to strong convection generated during sonication that assists effective transport of sugar molecules. Discrimination between individual contributions of ultrasound and cavitation to mass transfer enhancement reveals that contribution of ultrasound (through micro-streaming) is higher. Micro-turbulence as well as acoustic waves generated by cavitation did not contribute much to enhancing of mass transfer in the system.

AtObgC-AtRSH1 interaction may play a vital role in stress response signal transduction in Arabidopsis

The interaction of Obg (Spo0B-associated GTP-binding protein) GTPase and SpoT, which is a bifunctional ppGpp (guanosine 3',5'-bispyrophosphate) hydrolase/synthetase, is vital for the modulation of intracellular ppGpp levels during bacterial responses to environmental cues. It has been recently reported that the ppGpp level is also inducible by various stresses in the chloroplasts of plant cells. However, the function of the Obg-SpoT interaction in plants remains elusive. The results from the present and previous studies suggest that AtRSH1 is a putative bacterial SpoT homolog in Arabidopsis and that its transcription levels are responsive to wounding and salt stresses. In this study, we used a yeast two-hybrid analysis to map the regions required for the AtObgC-AtRSH1 interaction. Moreover, protein-protein docking simulations revealed reasonable geometric and electrostatic complementarity in the binding surfaces of the two proteins. The data support our experimental results, which suggest that the conserved domains in AtObgC and the N terminus of AtRSH1 containing the TGS domain contribute to their interaction. In addition, quantitative real-time PCR (qRT-PCR) analyses showed that the expression of AtObgC and AtRSH1 exhibit a similar inhibition pattern under wounding and salt-stress conditions, but the inhibition pattern was not greatly influenced by the presence or absence of light. Based on in vivo analyses, we further confirmed that the AtRSH1 and AtObgC proteins similarly localize in chloroplasts. Based on these results, we propose that the AtObgC-AtRSH1 interaction plays a vital role in ppGpp-mediated stress responses in chloroplasts.