Overexpression of ZmSTOP1-A Enhances Aluminum Tolerance in Arabidopsis by Stimulating Organic Acid Secretion and Reactive Oxygen Species Scavenging.

Aluminum (Al) toxicity and low pH are major factors limiting plant growth in acidic soils. Sensitive to Proton Rhizotoxicity 1 (STOP1) transcription factors respond to these stresses by regulating the expression of multiple Al- or low pH-responsive genes. ZmSTOP1-A, a STOP1-like protein from maize (Zea mays), was localized to the nucleus and showed transactivation activity. ZmSTOP1-A was expressed moderately in both roots and shoots of maize seedlings, but was not induced by Al stress or low pH. Overexpression of ZmSTOP1-A in Arabidopsis Atstop1 mutant partially restored Al tolerance and improved low pH tolerance with respect to root growth. Regarding Al tolerance, ZmSTOP1-A/Atstop1 plants showed clear upregulation of organic acid transporter genes, leading to increased organic acid secretion and reduced Al accumulation in roots. In addition, the antioxidant enzyme activity in roots and shoots of ZmSTOP1-A/Atstop1 plants was significantly enhanced, ultimately alleviating Al toxicity via scavenging reactive oxygen species. Similarly, ZmSTOP1-A could directly activate ZmMATE1 expression in maize, positively correlated with the number of Al-responsive GGNVS cis-elements in the ZmMATE1 promoter. Our results reveal that ZmSTOP1-A is an important transcription factor conferring Al tolerance by enhancing organic acid secretion and reactive oxygen species scavenging in Arabidopsis.

ZmNRAMP4 Enhances the Tolerance to Aluminum Stress in Arabidopsis thaliana.

Aluminum (Al) toxicity causes severe reduction in crop yields in acidic soil. The natural resistance-associated macrophage proteins (NRAMPs) play an important role in the transport of mineral elements in plants. Recently, OsNrat1 and SbNrat1 were reported specifically to transport trivalent Al ions. In this study, we functionally characterized ZmNRAMP4, a gene previously identified from RNA-Seq data from Al-treated maize roots, in response to Al exposure in maize. ZmNRAMP4 was predominantly expressed in root tips and was specifically induced by Al stress. Yeast cells expressing ZmNRAMP4 were hypersensitive to Al, which was associated with Al accumulation in yeast. Furthermore, overexpression of ZmNRAMP4 in Arabidopsis conferred transgenic plants with a significant increase in Al tolerance. However, expression of ZmNRAMP4, either in yeast or in Arabidopsis, had no effect on the response to cadmium stress. Taken together, these results underlined an internal tolerance mechanism involving ZmNRAMP4 to enhance Al tolerance via cytoplasmic sequestration of Al in maize.

Overexpression of the Aldehyde Dehydrogenase Gene ZmALDH Confers Aluminum Tolerance in Arabidopsis thaliana.

Aluminum (Al) toxicity is the main factor limiting plant growth and the yield of cereal crops in acidic soils. Al-induced oxidative stress could lead to the excessive accumulation of reactive oxygen species (ROS) and aldehydes in plants. Aldehyde dehydrogenase (ALDH) genes, which play an important role in detoxification of aldehydes when exposed to abiotic stress, have been identified in most species. However, little is known about the function of this gene family in the response to Al stress. Here, we identified an ALDH gene in maize, ZmALDH, involved in protection against Al-induced oxidative stress. Al stress up-regulated ZmALDH expression in both the roots and leaves. The expression of ZmALDH only responded to Al toxicity but not to other stresses including low pH and other metals. The heterologous overexpression of ZmALDH in Arabidopsis increased Al tolerance by promoting the ascorbate-glutathione cycle, increasing the transcript levels of antioxidant enzyme genes as well as the activities of their products, reducing MDA, and increasing free proline synthesis. The overexpression of ZmALDH also reduced Al accumulation in roots. Taken together, these findings suggest that ZmALDH participates in Al-induced oxidative stress and Al accumulation in roots, conferring Al tolerance in transgenic Arabidopsis.

Transcriptomic Analysis Reveals Candidate Genes Responding Maize Gray Leaf Spot Caused by Cercospora zeina.

Gray leaf spot (GLS), caused by the fungal pathogen Cercospora zeina (C. zeina), is one of the most destructive soil-borne diseases in maize (Zea mays L.), and severely reduces maize production in Southwest China. However, the mechanism of resistance to GLS is not clear and few resistant alleles have been identified. Two maize inbred lines, which were shown to be resistant (R6) and susceptible (S8) to GLS, were injected by C. zeina spore suspensions. Transcriptome analysis was carried out with leaf tissue at 0, 6, 24, 144, and 240 h after inoculation. Compared with 0 h of inoculation, a total of 667 and 419 stable common differentially expressed genes (DEGs) were found in the resistant and susceptible lines across the four timepoints, respectively. The DEGs were usually enriched in 'response to stimulus' and 'response to stress' in GO term analysis, and 'plant-pathogen interaction', 'MAPK signaling pathways', and 'plant hormone signal transduction' pathways, which were related to maize's response to GLS, were enriched in KEGG analysis. Weighted-Genes Co-expression Network Analysis (WGCNA) identified two modules, while twenty hub genes identified from these indicated that plant hormone signaling, calcium signaling pathways, and transcription factors played a central role in GLS sensing and response. Combing DEGs and QTL mapping, five genes were identified as the consensus genes for the resistance of GLS. Two genes, were both putative Leucine-rich repeat protein kinase family proteins, specifically expressed in R6. In summary, our results can provide resources for gene mining and exploring the mechanism of resistance to GLS in maize.

ZmXTH, a xyloglucan endotransglucosylase/hydrolase gene of maize, conferred aluminum tolerance in Arabidopsis.

Aluminum (Al) toxicity is one of the primary factors limiting crop production in acid soils worldwide. The cell wall is the major target of Al toxicity owing to the presence of many Al binding sites. Previous studies have found that XTH, encoding xyloglucan endohydrolase (XEH) and xyloglucan endotransglucosylase (XET), could participate in cell wall extension and affect the binding ability of the cell wall to Al by impeding the activities of these two enzymes. In this study, we found that ZmXTH, an XTH gene in maize, was involved in Al detoxification. The Al-induced up-regulation of ZmXTH occurred in the roots, prominently in the root tips. Additionally, the expression of ZmXTH was specifically induced by Al3+ but no other divalent or trivalent cations. Compared with the wild-type Arabidopsis, ZmXTH overexpressing plants grew more healthy and had decreased Al content in their root and root cell wall after Al stress. Overall, the results suggest that ZmXTH could confer the Al tolerance of transgenic Arabidopsis plants by reducing the Al accumulation in their roots and cell walls.

ZmMATE6 from maize encodes a citrate transporter that enhances aluminum tolerance in transgenic Arabidopsis thaliana.

The yields of cereal crops grown on acidic soils are often reduced by aluminum (Al) toxicity because the prevalence of toxic Al3+ cations increases as pH falls below 5.0. The Al-dependent release of citrate from resistant lines of maize is controlled by ZmMATE1 which encodes a multidrug and toxic compound extrusion (MATE) transporter protein. ZmMATE6 is another member of this family in maize whose expression is also increased by Al treatment. We investigated the function of this gene in more detail to determine whether it also contributes to Al resistance. Quantitative RT-PCR measurements found that ZmMATE6 was expressed in the roots and leaves of Al-resistant and sensitive inbred lines. Treatment with Al induced ZmMATE6 expression in all tissues but several other divalent or trivalent cations tested had no effect on expression. This expression pattern and the induction by Al treatment was confirmed in ZmMATE6 promoter-ß-glucuronidase fusion lines. Heterogeneous expression of ZmMATE6 displayed a greater Al-activated release of citrate from the roots and was significantly resistant to Al toxicity than controls. This was associated with reduced accumulation of Al in the root tissues. Our results demonstrated that ZmMATE6 expression is induced by Al and functions as a citrate transporter.

A Maize ZmAT6 Gene Confers Aluminum Tolerance via Reactive Oxygen Species Scavenging.

Aluminum (Al) toxicity is the primary limiting factor that affects crop yields in acid soil. However, the genes that contribute to the Al tolerance process in maize are still poorly understood. Previous studies have predicted that ZmAT6 is a novel protein which could be upregulated under Al stress condition. Here, we found that ZmAT6 is expressed in many tissues and organs and can be dramatically induced by Al in both the roots and shoots but particularly in the shoots. The overexpression of ZmAT6 in maize and Arabidopsis plants increased their root growth and reduced the accumulation of Al, suggesting the contribution of ZmAT6 to Al tolerance. Moreover, the ZmAT6 transgenic maize plants had lower contents of malondialdehyde and reactive oxygen species (ROS), but much higher proline content and even lower Evans blue absorption in the roots compared with the wild type. Furthermore, the activity of several enzymes of the antioxidant system, such as peroxidase (POD), superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX), increased in ZmAT6 transgenic maize plants, particularly SOD. Consistently, the expression of ZmSOD in transgenic maize was predominant upregulated by Al stress. Taken together, these findings revealed that ZmAT6 could at least partially confer enhanced tolerance to Al toxicity by scavenging ROS in maize.

tRNA-derived fragment tRF-03357 promotes cell proliferation, migration and invasion in high-grade serous ovarian cancer.

BACKGROUND: High-grade serous ovarian cancer (HGSOC) is one of the most common ovarian epithelial malignancies. tRNA-derived fragments (tRFs) have been identified as novel potential biomarkers and targets for cancer therapy. Nevertheless, the influence of tRFs on HGSOC remains unknown. This study aimed to identify HGSOC-associated tRFs and to investigate the function and mechanism of key tRFs in SK-OV-3 ovarian cancer cells. METHODS: The tRF profiles in HGSOC patients and controls were investigated using small RNA sequencing. Differentially expressed tRFs were verified by real-time PCR, and a key tRF was evaluated in a function study. RESULTS: A total of 27 tRFs were differentially expressed between HGSOC patients and controls. Differentially expressed tRFs were mainly involved in the functions of protein phosphorylation, transcription and cell migration and the pathway of cancer, and the MAPK and Wnt signaling pathways. Real-time PCR verified that tRF-03357 and tRF-03358 were significantly increased in the HGSOC serum samples and SK-OV-3 cells compared to their expression levels in the controls. Importantly, tRF-03357 promoted SK-OV-3 cell proliferation, migration and invasion. Moreover, tRF-03357 was predictively targeted, and significantly downregulated HMBOX1. CONCLUSION: This study suggests that tRF-03357 might promote cell proliferation, migration and invasion, partly by modulating HMBOX1 in HGSOC.

Adaptive reduction of human myometrium contractile activity in response to prolonged uterine stretch during term and twin pregnancy. Role of TREK-1 channel.

Quiescence of myometrium contractile activity allows uterine expansion to accommodate the growing fetus and prevents preterm labor particularly during excessive uterine stretch in multiple pregnancy. However, the mechanisms regulating uterine response to stretch are unclear. We tested the hypothesis that prolonged uterine stretch is associated with decreased myometrium contractile activity via activation of TWIK-related K+ channel (TREK-1). Pregnant women at different gestational age (preterm and term) and uterine stretch (singleton and twin pregnancy) were studied, and uterine strips were isolated for measurement of contractile activity and TREK-1 channel expression/activity. Both oxytocin- and KCl-induced contraction were reduced in term vs preterm pregnancy and in twin vs singleton pregnancy. Oxytocin contraction was reduced in uterine segments exposed to 8 g stretch compared to control tissues under 2 g basal tension. TREK-1 mRNA expression and protein levels were augmented in Singleton-Term vs Singleton-Preterm, and in uterine strips exposed to 8 g stretch. The TREK-1 activator arachidonic acid reduced oxytocin contraction in preterm and term, singleton and twin pregnant uterus. The TREK-1 blocker l-methionine enhanced oxytocin contraction in Singleton-Term and twin pregnant uterus, and reversed the decreases in contraction in uterine strips exposed to prolonged stretch. Carboprost-induced uterine contraction was also reduced by arachidonic acid and enhanced by l-methionine. Thus, myometrium contraction decreases with gestational age and uterine expansion in twin pregnancy. The results suggest that prolonged stretch enhances the expression/activity of TREK-1 channel, leading to decreased myometrium contractile activity and maintained healthy term pregnancy particularly in multiple pregnancy.

Progesterone inhibits contraction and increases TREK-1 potassium channel expression in late pregnant rat uterus.

OBJECTIVE: The aim of this study was to investigate the effect and mechanism by which progesterone regulates uterine contraction in late pregnant rats. RESULTS: Progesterone caused concentration-dependent relaxation of uterine strips that was enhanced compared with control nontreated uterine strips. Uterine strips incubated with progesterone showed a significant increase in TREK-1 mRNA expression and protein level. TREK-1 inhibitor L-methionine partly reversed uterine relaxation caused by the progesterone, while TREK-1 activator arachidonic acid did not cause significant change in progesterone-induced relaxation. CONCLUSIONS: Progesterone inhibits uterine contraction and induces uterine relaxation in late pregnancy. The progesterone-induced inhibition of uterine contraction appears to partly involve increased potassium channel TREK-1 expression/activity. MATERIALS AND METHODS: Uterus from late-pregnant rats (gestational day 19) was isolated, and uterine strips were prepared for isometric contraction measurement. Oxytocin-induced contraction was compared in uterine strips pretreated with different concentration of progesterone. TREK-1 potassium channel inhibitor L-methionine and TREK-1 agonist arachidonic acid were used to determine whether the changes caused by progesterone involve changes in TREK-1 activity. The mRNA and protein expression of TREK-1 in uterine tissues were measured using qPCR and Western blot.

The role of TRPP2 in agonist-induced gallbladder smooth muscle contraction.

TRPP2 channel protein belongs to the superfamily of transient receptor potential (TRP) channels and is widely expressed in various tissues, including smooth muscle in digestive gut. Accumulating evidence has demonstrated that TRPP2 can mediate Ca(2+) release from Ca(2+) stores. However, the functional role of TRPP2 in gallbladder smooth muscle contraction still remains unclear. In this study, we used Ca(2+) imaging and tension measurements to test agonist-induced intracellular Ca(2+) concentration increase and smooth muscle contraction of guinea pig gallbladder, respectively. When TRPP2 protein was knocked down in gallbladder muscle strips from guinea pig, carbachol (CCh)-evoked Ca(2+) release and extracellular Ca(2+) influx were reduced significantly, and gallbladder contractions induced by endothelin 1 and cholecystokinin were suppressed markedly as well. CCh-induced gallbladder contraction was markedly suppressed by pretreatment with U73122, which inhibits phospholipase C to terminate inositol 1,4,5-trisphosphate receptor (IP3) production, and 2-aminoethoxydiphenyl borate (2APB), which inhibits IP3 recepor (IP3R) to abolish IP3R-mediated Ca(2+) release. To confirm the role of Ca(2+) release in CCh-induced gallbladder contraction, we used thapsigargin (TG)-to deplete Ca(2+) stores via inhibiting sarco/endoplasmic reticulum Ca(2+)-ATPase and eliminate the role of store-operated Ca(2+) entry on the CCh-induced gallbladder contraction. Preincubation with 2 µmol L(-1) TG significantly decreased the CCh-induced gallbladder contraction. In addition, pretreatments with U73122, 2APB or TG abolished the difference of the CCh-induced gallbladder contraction between TRPP2 knockdown and control groups. We conclude that TRPP2 mediates Ca(2+) release from intracellular Ca(2+) stores, and has an essential role in agonist-induced gallbladder muscle contraction.