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Mitochondrial small heat shock protein mediates seed germination via thermal sensing.

ABSTRACT: Seed germination is an energy demanding process that requires functional mitochondria upon imbibition. However, how mitochondria fine tune seed germination, especially in response to the dynamics of environmental temperature, remains largely unknown at the molecular level. Here, we report a mitochondrial matrix-localized heat shock protein GhHSP24.7, that regulates seed germination in a temperature-dependent manner. Suppression of GhHSP24.7 renders the seed insensitive to temperature changes and delays germination. We show that GhHSP24.7 competes with GhCCMH to bind to the maturation subunit protein GhCcmF_c to form cytochrome C/C₁ (CytC/C₁) in the mitochondrial electron transport chain. GhHSP24.7 modulates CytC/C₁ production to induce reactive oxygen species (ROS) generation, which consequently accelerates endosperm rupture and promotes seed germination. Overexpression of GhHSP24.7's homologous genes can accelerate seed germination in Arabidopsis and tomato, indicating its conserved function across plant species. Therefore, HSP24.7 is a critical factor that positively controls seed germination via temperature-dependent ROS generation.

SUBMITTER: Ma W

PROVIDER: S-EPMC6410843 | biostudies-literature | 2019 Mar

REPOSITORIES: biostudies-literature

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Mitochondrial small heat shock protein mediates seed germination via thermal sensing.

Ma Wei W Guan Xueying X Li Jie J Pan Ronghui R Wang Luyao L Liu Fengjun F Ma Hongyu H Zhu Shuijin S Hu Jin J Ruan Yong-Ling YL Chen Xiaoya X Zhang Tianzhen T

Proceedings of the National Academy of Sciences of the United States of America 20190214 10

Seed germination is an energy demanding process that requires functional mitochondria upon imbibition. However, how mitochondria fine tune seed germination, especially in response to the dynamics of environmental temperature, remains largely unknown at the molecular level. Here, we report a mitochondrial matrix-localized heat shock protein GhHSP24.7, that regulates seed germination in a temperature-dependent manner. Suppression of <i>GhHSP24.7</i> renders the seed insensitive to temperature chan ...[more]

PMID: 30765516

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Project description:Seed germination is a critical phase during which plants are particularly sensitive to environmental stresses, especially heat stress, due to the high metabolic and physiological activities required for initial growth. Melatonin (MT), a key antioxidant, is crucial for assisting plants in managing abiotic stresses. While the impact of melatonin on heat stress has been explored in other developmental stages or species, this is the first study to specifically focus on its role during maize seed germination under heat stress. The treatment with 50 μM melatonin significantly enhanced seed germination under heat stress by improving antioxidant capacity, osmotic regulation, and hydrolytic enzyme activity, likely through the modulation of key signaling pathways, thus reducing oxidative damage and starch content. Furthermore, melatonin application promoted the accumulation of endogenous gibberellins (GAs) and significantly inhibited abscisic acid (ABA) content, thereby maintaining a dynamic equilibrium between these phytohormones. Principal component analysis and correlation analysis provided deeper insights into the overall effects of these physiological and biochemical parameters. Integrated transcriptomic and metabolomic analysis revealed that melatonin exerted its regulatory effects by modulating key genes and pathways associated with antioxidant defense, stress responses, and plant hormone signal transduction. Furthermore, melatonin significantly modulated the GA and ABA signaling pathways, starch and sucrose metabolism, and phenylpropanoid biosynthesis, thereby reducing oxidative damage induced by heat stress and strengthening the defense mechanisms of maize seeds. The alignment between the qRT-PCR findings and transcriptomic data further validated the robustness of these underlying mechanisms. In conclusion, this study provides novel insights into the role of melatonin in enhancing maize seed germination under heat stress and offers a promising strategy for improving crop heat tolerance through melatonin application in agricultural practices.

Project description:The rapid increase in heat shock proteins upon exposure to damaging stresses and during plant development related to desiccation events reveal their dual importance in plant development and stress tolerance. Genome-wide sequence survey identified 20 non-redundant small heat shock proteins (sHsp) and 22 heat shock factor (Hsf) genes in barley. While all three major classes (A, B, C) of Hsfs are localized in nucleus, the 20 sHsp gene family members are localized in different cell organelles like cytoplasm, mitochondria, plastid and peroxisomes. Hsf and sHsp members are differentially regulated during drought and at different seed developmental stages suggesting the importance of chaperone role under drought as well as seed development. In silico cis-regulatory motif analysis of Hsf promoters showed an enrichment with abscisic acid responsive cis-elements (ABRE), implying regulatory role of ABA in mediating transcriptional response of HvsHsf genes. Gene regulatory network analysis identified HvHsfB2c as potential central regulator of the seed-specific expression of several HvsHsps including 17.5CI sHsp. These results indicate that HvHsfB2c is co-expressed in the central hub of small Hsps and therefore it may be regulating the expression of several HvsHsp subclasses HvHsp16.88-CI, HvHsp17.5-CI and HvHsp17.7-CI. The in vivo relevance of binding specificity of HvHsfB2C transcription factor to HSE-element present in the promoter of HvSHP17.5-CI under heat stress exposure is confirmed by gel shift and LUC-reporter assays. Further, we isolated 477 bp cDNA from barley encoding a 17.5 sHsp polypeptide, which was predominantly upregulated under drought stress treatments and also preferentially expressed in developing seeds. Recombinant HvsHsp17.5-CI protein was expressed in E. coli and purified to homogeneity, which displayed in vitro chaperone activity. The predicted structural model of HvsHsp-17.5-CI protein suggests that the α-crystallin domain is evolutionarily highly conserved.

Project description:Small heat shock proteins (sHsps) have multiple cellular functions. However, the biological function of sHsps in pathogenic microorganisms is largely unknown. In the present study we identified and characterized the novel sHsp Hsp21 of the human fungal pathogen Candida albicans. Using a reverse genetics approach we demonstrate the importance of Hsp21 for resistance of C. albicans to specific stresses, including thermal and oxidative stress. Furthermore, a hsp21?/? mutant was defective in invasive growth and formed significantly shorter filaments compared to the wild type under various filament-inducing conditions. Although adhesion to and invasion into human-derived endothelial and oral epithelial cells was unaltered, the hsp21?/? mutant exhibited a strongly reduced capacity to damage both cell lines. Furthermore, Hsp21 was required for resisting killing by human neutrophils. Measurements of intracellular levels of stress protective molecules demonstrated that Hsp21 is involved in both glycerol and glycogen regulation and plays a major role in trehalose homeostasis in response to elevated temperatures. Mutants defective in trehalose and, to a lesser extent, glycerol synthesis phenocopied HSP21 deletion in terms of increased susceptibility to environmental stress, strongly impaired capacity to damage epithelial cells and increased sensitivity to the killing activities of human primary neutrophils. Via systematic analysis of the three main C. albicans stress-responsive kinases (Mkc1, Cek1, Hog1) under a range of stressors, we demonstrate Hsp21-dependent phosphorylation of Cek1 in response to elevated temperatures. Finally, the hsp21?/? mutant displayed strongly attenuated virulence in two in vivo infection models. Taken together, Hsp21 mediates adaptation to specific stresses via fine-tuning homeostasis of compatible solutes and activation of the Cek1 pathway, and is crucial for multiple stages of C. albicans pathogenicity. Hsp21 therefore represents the first reported example of a small heat shock protein functioning as a virulence factor in a eukaryotic pathogen.

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Mitochondrial small heat shock protein mediates seed germination via thermal sensing.

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Mitochondrial small heat shock protein mediates seed germination via thermal sensing.

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