Knockdown of CaHSP60-6 confers enhanced sensitivity to heat stress in pepper (Capsicum annuum L.).

MAIN CONCLUSION: HSP60 gene family in pepper was analyzed through bioinformatics along with transcriptional regulation against multiple abiotic and hormonal stresses. Furthermore, the knockdown of CaHSP60-6 increased sensitivity to heat stress. The 60 kDa heat shock protein (HSP60) also known as chaperonin (cpn60) is encoded by multi-gene family that plays an important role in plant growth, development and in stress response as a molecular chaperone. However, little is known about the HSP60 gene family in pepper (Capsicum annuum L.). In this study, 16 putative pepper HSP60 genes were identified through bioinformatic tools. The phylogenetic tree revealed that eight of the pepper HSP60 genes (50%) clustered into group I, three (19%) into group II, and five (31%) into group III. Twelve (75%) CaHSP60 genes have more than 10 introns, while only a single gene contained no introns. Chromosomal mapping revealed that the tandem and segmental duplication events occurred in the process of evolution. Gene ontology enrichment analysis predicted that CaHSP60 genes were responsible for protein folding and refolding in an ATP-dependent manner in response to various stresses in the biological processes category. Multiple stress-related cis-regulatory elements were found in the promoter region of these CaHSP60 genes, which indicated that these genes were regulated in response to multiple stresses. Tissue-specific expression was studied under normal conditions and induced under 2 h of heat stress measured by RNA-Seq data and qRT-PCR in different tissues (roots, stems, leaves, and flowers). The data implied that HSP60 genes play a crucial role in pepper growth, development, and stress responses. Fifteen (93%) CaHSP60 genes were induced in both, thermo-sensitive B6 and thermo-tolerant R9 lines under heat treatment. The relative expression of nine representative CaHSP60 genes in response to other abiotic stresses (cold, NaCl, and mannitol) and hormonal applications [ABA, methyl jasmonate (MeJA), and salicylic acid (SA)] was also evaluated. Knockdown of CaHSP60-6 increased the sensitivity to heat shock treatment as documented by a higher relative electrolyte leakage, lipid peroxidation, and reactive oxygen species accumulation in silenced pepper plants along with a substantial lower chlorophyll content and antioxidant enzyme activity. These results suggested that HSP60 might act as a positive regulator in pepper defense against heat and other abiotic stresses. Our results provide a basis for further functional analysis of HSP60 genes in pepper.

UPLC-MS/MS Assay for Quantification of Wedelolactone and Demethylwedelolactone in Rat Plasma and the Application to a Preclinical Pharmacokinetic Study.

AIMS AND OBJECTIVE: Wedelolactone and demethylwedelolactone are the two major coumarin constituents of Herba Ecliptae. The objective of this work was to develop and validate a sensitive, rapid, and robust UPLC-MS/MS method for the simultaneous quantification of wedelolactone and demethylwedelolactone in rat plasma. MATERIALS AND METHODS: Wedelolactone and demethylwedelolactone were extracted from rat plasma by protein precipitation with acetonitrile. Electrospray ionization in negative mode and selected reaction monitoring (SRM) were used for wedelolactone and demethylwedelolactone at the transitions m/z 312.8→298.0 and m/z 299.1→270.6, respectively. Chromatographic separation was conducted on a Venusil C18 column (50 mm × 2.1 mm, 5 µm) with isocratic elution of acetonitrile-0.1% formic acid in water (55:45, v/v) at a flow rate of 0.3 mL/min. A linear range was observed over the concentration range of 0.25-100 ng/mL for wedelolactone and demethylwedelolactone. RESULTS: They reached their maximum plasma concentrations (Cmax, 74.9±13.4 ng/mL for wedelolactone and 41.3±9.57 ng/mL for demethylwedelolactone) at the peak time (Tmax) of 0.633 h and 0.800 h, respectively. The AUC0-t value of wedelolactone (260.8±141.8 ng h/mL) was higher than that of demethylwedelolactone (127.4±52.7 ng h/mL) by approximately 2-fold, whereas the terminal elimination half-life (t1/2) of wedelolactone (2.20±0.59 h) showed the approximately same as that of demethylwedelolactone (2.08±0.69 h). CONCLUSION: Based on full validation according to US FDA guidelines, this UPLC-MS/MS method was successfully applied to a pharmacokinetic study in rats.

CaHSP16.4, a small heat shock protein gene in pepper, is involved in heat and drought tolerance.

Environmental stress affects growth and development of crops, and reduces yield and quality of crops. To cope with environmental stressors, plants have sophisticated defense mechanisms, including the HSF/HSP pathway. Here, we identify the expression pattern of CaHSP16.4 in thermo-tolerant and thermo-sensitive pepper (Capsicum annuum L.) lines. Under heat stress, R9 thermo-tolerant line had higher CaHSP16.4 expression level than the B6 thermo-sensitive line. Under drought stress, expression pattern of CaHSP16.4 was dynamic. Initially, CaHSP16.4 was downregulated then CaHSP16.4 significantly increased. Subcellular localization assay showed that CaHSP16.4 localizes in cytoplasm and nucleus. In the R9 line, silencing of CaHSP16.4 resulted in a significant increase in malonaldehyde content and a significant reduction in total chlorophyll content, suggesting that silencing of CaHSP16.4 reduces heat and drought stresses tolerance. Overexpression of CaHSP16.4 enhances tolerance to heat stress in Arabidopsis. Under heat stress, the survival rate of CaHSP16.4 overexpression lines was significantly higher than wild type. Furthermore, under heat, drought, and combined stress conditions, the CaHSP16.4-overexpression lines had lower relative electrolytic leakage and malonaldehyde content, higher total chlorophyll content, and higher activity levels of superoxide dismutase, catalase, ascorbic acid peroxidase, and glutathione peroxidase compared to wild type. Furthermore, the expression levels of the stress response genes in the overexpression lines were higher than the wild type. These results indicate that the overexpression of CaHSP16.4 enhances the ability of reactive oxygen species scavenging under heat and drought stress.

A small heat shock protein CaHsp25.9 positively regulates heat, salt, and drought stress tolerance in pepper (Capsicum annuum L.).

Extreme environmental conditions seriously affect crop growth and development, resulting in a decrease in crop yield and quality. However, small heat shock proteins (Hsp20s) play an important role in helping plants to avoid these negative impacts. In this study, we identified the expression pattern of the CaHsp25.9 gene in a thermo-tolerance pepper line R9 and thermo-sensitive line B6. The transcription of CaHsp25.9 was strongly induced by heat stress in both R9 and B6. The expression of CaHsp25.9 was induced by salt and drought stress in R9. Additionally, the CaHsp25.9 protein was localized in the cell membrane and cytoplasm. When silencing the CaHsp25.9 gene in the R9 line, the accumulation of malonaldehyde (MDA), relative electrolytic leakage, hydrogen peroxide, superoxide anion were increased, while total chlorophyll decreased under heat, salt, and drought stress. Over-expression of CaHsp25.9 in Arabidopsis resulted in decreased MDA, while proline, superoxide dismutase activity, germination, and root length increased under heat, salt, and drought stress. However, peroxidase activity was higher in drought stress but lower in heat and salt stress in transgenic Arabidopsis compared to the wild type (WT). Furthermore, the transcription of stress related genes was more highly induced in transgenic lines than WT. Our results indicated that CaHsp25.9 confers heat, salt, and drought stress tolerance to plants by reducing the accumulation of reactive oxygen species, enhancing the activity of antioxidant enzymes, and regulating the expression of stress-related genes. Therefore, these results may provide insight into plant adaption mechanisms developed in variable environments.