Regulatory roles of microRNA163 in responses to stresses in Arabidopsis.

MicroRNAs (miRNAs) are small regulatory RNAs that participate in various biological processes by silencing target genes. In Arabidopsis, microRNA163 (miR163) was found to be involved in seed germination, root development, and biotic resistance. However, the regulatory roles of miR163 remain unclear. In the current study, the mir163 mutant was investigated to comprehensively understand and characterize its functions in Arabidopsis. RNA-sequencing and Gene Ontology enrichment analyses revealed that miR163 might be involved in "response to stimulus" and "metabolic process". Interestingly, "response to stress", including heat, cold, and oxidative stress, was enriched under the subcategory of "response to stimulus". We observed that miR163 and PXMT were repressed and induced under heat stress, respectively. Furthermore, the study detected significant differences in seed germination rate, hypocotyl length, and survival rate, indicating a variation in the thermotolerance between WT and mir163 mutant. The results revealed that the mir163 mutant had a lesser degree of germination inhibition by heat treatment than WT. In addition, the mir163 mutant showed a better survival rate and longer hypocotyl length under heat treatment than the WT. The metabolomes of WT and mir163 mutant were further analyzed. The contents of benzene derivatives and flavonoids were affected by miR163, which could enhance plants' defense abilities. In conclusion, miR163/targets regulated the expression of stress-responsive genes and the accumulation of defense-related metabolites to alter stress tolerance.

Review: Defense responses in sweetpotato (Ipomoea batatas L.) against biotic stress.

Sweetpotato (Ipomoea batatas L.) is regarded as amongst the world's most important crops for food, vegetable, forage, and raw material for starch and alcohol production. Since pest attack and disease infection are the main limiting aspects frequently causing the yield loss and quality degradation of sweetpotato, it is a great demand to develop the effective defense strategies for maintaining productivity. In the past decade, many studies have focused on dynamic analysis at the physiological, biochemical, and molecular responses of sweetpotatoes to environmental challenges. This review offers an overview of the defense mechanisms against biotic stresses in sweetpotato observed so far, particularly insect herbivory and pathogen infections. The defenses of sweetpotato include the regulation of the toxic and anti-digestive proteins, plant-derived compounds, physical barrier formation, and sugar distribution. Ipomoelin and sporamin have been extensively researched for the defense against herbivore wounding. Herbivory-induced plant volatiles, chlorogenic acid, and latex phytochemicals play important roles in defenses for insect herbivory. Induction of IbSWEET10 reduces sugar content to mediate F. oxysporum resistance. Therefore, these researches provide the genetic strategies for improving resistance bioengineering and breeding of sweetpotato crops and future prospects for research in this field.

Involvement of microRNA164 in responses to heat stress in Arabidopsis.

MicroRNAs (miRNAs) are considered to be integral parts of plant stress regulatory networks. Under long-term heat stress, miR164 is induced. Conversely, its targets are repressed. Transgenic overexpressors (164OE) and mutants of MIR164 (mir164) were used to study miR164's functions during heat responses. Target gene expression decreased in 164OE transgenic plants and increased in mir164a-4 and mir164b mutants. Under heat stress, the mir164 mutants presented heat-sensitive phenotypes, while 164OE transgenic plants showed better thermotolerance than wild-type (WT) plants. Overexpression of miR164 decreased heat-inhibition of hypocotyl lengths. Under heat stress, miR164 target genes modulated the expression of chlorophyll b reductase and chlorophyll catabolic genes, reducing the chlorophyll a/b ratio. More H2O2 accumulated in the mir164 mutants under heat stress, which may have caused oxidative damage. In addition, expression of HSPs was altered in the experimental plants compared to that of the WT. Overall, miR164 influenced target gene expression, altering development, chlorophyll a/b ratio, H2O2-caused damage, and HSPs expression under long-term heat stress. These phenomena, in turn, likely influence the thermotolerance of plants.

IbTLD modulates reactive oxygen species scavenging and DNA protection to confer salinity stress tolerance in tobacco.

Plants accumulate reactive oxygen species (ROS) that may damage the cells under prolonged stress conditions. Reduction of the excessive ROS production can alleviate oxidative damage and enhance the survival rates under stress. TLDc-containing protein (TLD) was reported to confer tolerance to oxidative stress, but the regulatory mechanism of TLD remains unclear. In this study, we ectopically overexpressed the Ipomoea batatas TLDc gene (IbTLD) in tobacco and characterized its functions. RNA-sequencing analysis and Gene Ontology term enrichment analysis revealed that IbTLD up-regulates auxin-responsive genes in response to oxidative stress. Under salinity stress, the IbTLD transgenic lines showed higher germination rates, chlorophyll contents, and root lengths than wild type (W38). In addition, the IbTLD transgenic lines showed higher expression of ROS scavenging genes, nudix hydrolases, ROS scavenging enzyme activity, and lesser DNA damage compared to W38 under salinity stress. Therefore, our results suggest that IbTLD activates the expression of ROS scavenging genes and confers tolerance to salinity stress in planta.

Large-scale data analysis for robotic yeast one-hybrid platforms and multi-disciplinary studies using GateMultiplex.

BACKGROUND: Yeast one-hybrid (Y1H) is a common technique for identifying DNA-protein interactions, and robotic platforms have been developed for high-throughput analyses to unravel the gene regulatory networks in many organisms. Use of these high-throughput techniques has led to the generation of increasingly large datasets, and several software packages have been developed to analyze such data. We previously established the currently most efficient Y1H system, meiosis-directed Y1H; however, the available software tools were not designed for processing the additional parameters suggested by meiosis-directed Y1H to avoid false positives and required programming skills for operation. RESULTS: We developed a new tool named GateMultiplex with high computing performance using C++. GateMultiplex incorporated a graphical user interface (GUI), which allows the operation without any programming skills. Flexible parameter options were designed for multiple experimental purposes to enable the application of GateMultiplex even beyond Y1H platforms. We further demonstrated the data analysis from other three fields using GateMultiplex, the identification of lead compounds in preclinical cancer drug discovery, the crop line selection in precision agriculture, and the ocean pollution detection from deep-sea fishery. CONCLUSIONS: The user-friendly GUI, fast C++ computing speed, flexible parameter setting, and applicability of GateMultiplex facilitate the feasibility of large-scale data analysis in life science fields.

Priming of Plant Resistance to Heat Stress and Tomato Yellow Leaf Curl Thailand Virus With Plant-Derived Materials.

Plants are often simultaneously exposed to diverse environmental stresses, and can tune suitable responses to them through hormones. Salicylic acid (SA) and jasmonic acid (JA) signaling pathways are known to enhance resistance against heat stress and tomato yellow leaf curl Thailand virus (TYLCTHV) infection. However, there is limited information regarding alternative natural priming agents against heat stress and viruses. In this study, two plant-derived priming agents, eugenol and anise oil, were tested for their roles in conferring thermotolerance and virus resistance in tomato plants. Under heat stress, the survival rates and average fresh weight were higher in plants treated with eugenol or anise oil than in control plants. These two priming agents were further tested for antiviral activities. After TYLCTHV infection, the disease incidence and relative abundance of TYLCTHV were lower in anise oil- and eugenol-treated plants than in control plants. Further analyses revealed that a few SA, JA, and RNA silencing genes were enhanced in the former. Moreover, SA, JA, and H2O2 contents increased considerably after eugenol and anise oil treatments. Our findings imply that anise oil and eugenol initiated SA- and JA-mediated defenses to promote thermotolerance and antiviral responses of tomato plants.

The p38-like MAP kinase modulated H2O2 accumulation in wounding signaling pathways of sweet potato.

In sweet potato (Ipomoea batatas cv Tainung 57), MAPK cascades are involved in the regulation of Ipomoelin (IPO) expression upon wounding. p38 MAPK plays an important role in plant's responses to various environmental stresses. However, the role of p38-like MAPK in wounding response is still unknown. In this study, the levels of phosphorylated-p38-like MAPK (pp38-like MAPK) in sweet potato were noticeably reduced after wounding. In addition, SB203580 (SB), a specific inhibitor blocking p38 MAPK phosphorylation, considerably decreased the accumulation of pp38-like MAPK. Expression of a wound-inducible gene IPO was elevated by SB. Moreover, it stimulated hydrogen peroxide (H2O2) production rather than cytosolic Ca2+ elevation in sweet potato leaves. However, NADPH oxidase (NOX) inhibitor diphenyleneiodonium could not inhibit IPO induction stimulated by SB. These results indicated a p38-like MAPK mechanism was involved in the regulation of IPO expression through NOX-independent H2O2 generation. In addition, the presence of the protein phosphatase inhibitor okadaic acid or the MEK1/ERK inhibitor PD98059 repressed the H2O2- or SB-induced IPO expression, demonstrating phosphatase(s) and MEK1/ERK functioning in the downstream of H2O2 and pp38-like MAPK in the signal transduction pathway stimulating IPO. Conclusively, wounding decreased the amount of pp38-like MAPK, stimulated H2O2 production, and then induced IPO expression.

MicroR408 regulates defense response upon wounding in sweet potato.

MiRNAs play diverse roles in plant development and defense responses by binding to their mRNA targets based on sequence complementarity. Here, we investigated a wound-related miR408 and its target genes in sweet potato (Ipomoea batatas) by small RNA deep sequencing and transcriptome analysis. The expression patterns of miR408 and the miR408 precursor were significantly repressed by wounding and jasmonate (JA). In contrast, expression of the putative target genes IbKCS (3-ketoacyl-CoA synthase 4), IbPCL (plantacyanin), and IbGAUT (galacturonosyltransferase 7-like) of miR408 was increased following wounding, whereas only IbKCS was increased after JA treatment. Target cleavage site mapping and Agrobacterium-mediated transient assay demonstrated that IbKCS, IbPCL, and IbGAUT were the targets of miR408. The expression of miR408 target genes was repressed in transgenic sweet potatoes overexpressing miR408. These data indicated a relationship between miR408 and its target genes. Notably, miR408-overexpressing plants showed a semi-dwarf phenotype and attenuated resistance to insect feeding, while transgenic plants overexpressing IbKCS exhibited more insect resistance than plants overexpressing only the empty vector. Collectively, sweet potato reduces the abundance of miR408 upon wounding to elevate the expression of IbKCS, IbPCL, and IbGAUT. The expression of IbKCS enhances the defense system against herbivore wounding.

MicroRNA160 Modulates Plant Development and Heat Shock Protein Gene Expression to Mediate Heat Tolerance in Arabidopsis.

Global warming is causing a negative impact on plant growth and adversely impacts on crop yield. MicroRNAs (miRNAs) are critical in regulating the expression of genes involved in plant development as well as defense responses. The effects of miRNAs on heat-stressed Arabidopsis warrants further investigation. Heat stress increased the expression of miR160 and its precursors but considerably reduced that of its targets, ARF10, ARF16, and ARF17. To study the roles of miR160 during heat stress, transgenic Arabidopsis plants overexpressing miR160 precursor a (160OE) and artificial miR160 (MIM160), which mimics an inhibitor of miR160, were created. T-DNA insertion mutants of miR160 targets were also used to examine their tolerances to heat stress. Results presented that overexpressing miR160 improved seed germination and seedling survival under heat stress. The lengths of hypocotyl elongation and rachis were also longer in 160OE than the wild-type (WT) plants under heat stress. Interestingly, MIM160 plants showed worse adaption to heat. In addition, arf10, arf16, and arf17 mutants presented similar phenotypes to 160OE under heat stress to advance abilities of thermotolerance. Moreover, transcriptome and qRT-PCR analyses revealed that HSP17.6A, HSP17.6II, HSP21, and HSP70B expression levels were regulated by heat in 160OE, MIM160, arf10, arf16, and arf17 plants. Hence, miR160 altered the expression of the heat shock proteins and plant development to allow plants to survive heat stress.

Signal transduction and regulation of IbpreproHypSys in sweet potato.

Hydroxyproline-rich glycopeptides (HypSys) are small signalling peptides containing 18-20 amino acids. The expression of IbpreproHypSys, encoding the precursor of IbHypSys, was induced in sweet potato (Ipomoea batatas cv. Tainung 57) through wounding and IbHypSys treatments by using jasmonate and H2 O2 . Transgenic sweet potatoes overexpressing (OE) and silencing [RNA interference (RNAi)] IbpreproHypSys were created. The expression of the wound-inducible gene for ipomoelin (IPO) in the local and systemic leaves of OE plants was stronger than the expression in wild-type (WT) and RNAi plants after wounding. Furthermore, grafting experiments indicated that IPO expression was considerably higher in WT stocks receiving wounding signals from OE than from RNAi scions. However, wounding WT scions highly induced IPO expression in OE stocks. These results indicated that IbpreproHypSys expression contributed towards sending and receiving the systemic signals that induced IPO expression. Analysing the genes involved in the phenylpropanoid pathway demonstrated that lignin biosynthesis was activated after synthetic IbHypSys treatment. IbpreproHypSys expression in sweet potato suppressed Spodoptera litura growth. In conclusion, wounding induced the expression of IbpreproHypSys, whose protein product was processed into IbHypSys. IbHypSys stimulated IbpreproHypSys and IPO expression and enhanced lignin biosynthesis, thus protecting plants from insects.

Carbon monoxide regulates the expression of the wound-inducible gene ipomoelin through antioxidation and MAPK phosphorylation in sweet potato.

Carbon monoxide (CO), one of the haem oxygenase (HO) products, plays important roles in plant development and stress adaptation. However, the function of CO involved in wounding responses is seldom studied. A wound-inducible gene, ipomoelin (IPO), of sweet potato (Ipomoea batatas cv. Tainung 57) was used as a target to study the regulation of CO in wounding responses. After wounding for 1h, the endogenous CO content and IbHO expression level were significantly reduced in leaves. IPO expression upon wounding was prohibited by the HO activator hemin, whereas the HO inhibitor zinc protoporphyrin IX elevated IPO expression. The IPO expression induced by wounding, H2O2, or methyl jasmonate was inhibited by CO. CO also affected the activities of ascorbate peroxidase, catalase, and peroxidase, and largely decreased H2O2 content in leaves. CO inhibited the extracellular signal-regulated kinase (ERK) phosphorylation induced by wounding. IbMAPK, the ERK of sweet potato, was identified by immunoblotting, and the interaction with its upstream activator, IbMEK1, was further confirmed by bimolecular fluorescence complementation and co-immunoprecipitation. Conclusively, wounding in leaves repressed IbHO expression and CO production, induced H2O2 generation and ERK phosphorylation, and then stimulated IPO expression.

Expression of a gene encoding ß-ureidopropionase is critical for pollen germination in tomatoes.

Global warming has seriously decreased world crop yield. High temperatures affect development, growth and, particularly, reproductive tissues in plants. A gene encoding ß-ureidopropionase (SlUPB1, EC 3.5.1.6) was isolated from the stamens of a heat-tolerant tomato (CL5915) using suppression subtractive hybridization. SlUPB1 catalyzes the production of ß-alanine, the only ß-form amino acid in nature. In the anthesis stage, SlUPB1 expression in CL5915 stamens, growing at 35/30°C (day/night), was 2.16 and 2.93 times greater than that in a heat-sensitive tomato (L4783) cultivated at 30/25°C or 25/20°C, respectively. Transgenic tomatoes, upregulating SlUPB1 in L4783 and downregulating SlUPB1 in CL5915, were constructed, and the amount of ß-alanine measured by liquid chromatography-electrospray ionization-mass spectrometry in the transgenic overexpression of SlUPB1 was higher than that of L4783. However, the ß-alanine in the transgenics downregulating SlUPB1 was significantly lower than the ß-alanine of CL5915. Pollen germination rates of these transgenics were analyzed under different developmental and germinating temperatures. The results indicated that germination rates of transgenics overexpressing SlUPB1 were higher than germination rates of the background tomato L4783. Germination rates of transgenics downregulating SlUPB1 were significantly lower than germination rates of background tomato CL5915, indicating the necessity of functional SlUPB1 for pollen germination. Pollen germinating in the buffer with the addition of ß-alanine further indicated that ß-alanine effectively enhanced pollen germination in tomatoes with low SlUPB1 expression. Together, these results showed that the expression of SlUPB1 is important for pollen germination, and ß-alanine may play a role in pollen germination under both optimal and high temperatures.

Interaction of small RNA-8105 and the intron of IbMYB1 RNA regulates IbMYB1 family genes through secondary siRNAs and DNA methylation after wounding.

Small RNAs (sRNAs) play important roles in plants under stress conditions. However, limited research has been performed on the sRNAs involved in plant wound responses. In the present study, a novel wounding-induced sRNA, sRNA8105, was identified in sweet potato (Ipomoea batatas cv. Tainung 57) using microarray analysis. It was found that expression of sRNA8105 increased after mechanical wounding. Furthermore, Dicer-like 1 (DCL1) is required for the sRNA8105 precursor (pre-sRNA8105) to generate 22 and 24 nt mature sRNA8105. sRNA8105 targeted the first intron of IbMYB1 (MYB domain protein 1) before RNA splicing, and mediated RNA cleavage and DNA methylation of IbMYB1. The interaction between sRNA8105 and IbMYB1 was confirmed by cleavage site mapping, agro-infiltration analyses, and use of a transgenic sweet potato over-expressing pre-sRNA8105 gene. Induction of IbMYB1-siRNA was observed in the wild-type upon wounding and in transgenic sweet potato over-expressing pre-sRNA8105 gene without wounding, resulting in decreased expression of the whole IbMYB1 gene family, i.e. IbMYB1 and the IbMYB2 genes, and thus directing metabolic flux toward biosynthesis of lignin in the phenylpropanoid pathway. In conclusion, sRNA8105 induced by wounding binds to the first intron of IbMYB1 RNA to methylate IbMYB1, cleave IbMYB1 RNA, and trigger production of secondary siRNAs, further repressing the expression of the IbMYB1 family genes and regulating the phenylpropanoid pathway.

MicroR828 regulates lignin and H2O2 accumulation in sweet potato on wounding.

MicroRNAs (miRNAs) are small noncoding RNAs which post-transcriptionally regulate gene expression by directing mRNA cleavage or translational inhibition. miRNAs play multiple roles in the growth, development and stress responses in plants. However, little is known of the wounding-responsive miRNAs and their regulation. Here, we investigated the expression patterns of microR828 (miR828) on wounding in sweet potato (Ipomoea batatas cv Tainung 57). The expression of miR828 was only detected in leaves, and was induced by wounding rather than by ethylene, hydrogen peroxide (H2O2), methyl jasmonate or nitric oxide (NO). Moreover, cyclic guanosine monophosphate (cGMP) was necessary for miR828 accumulation in leaves on wounding. Two miR828 target candidates, named IbMYB and IbTLD, were obtained by cDNA cloning, and their mRNA cleavage caused by miR828 was confirmed by cleavage site mapping, agro-infiltration and transgenics studies. The reduction in IbMYB and IbTLD expression coincided with the induction of miR828, demonstrating that IbMYB and IbTLD might be miR828 targets. Furthermore, transgenic sweet potato overexpressing miR828 precursor affected lignin and H2O2 contents. These results showed that cGMP could regulate wounding-responsive miR828, which repressed the expression of IbMYB and IbTLD. Subsequently, lignin and H2O2 were accumulated to participate in defense mechanisms.

Nitric oxide activates superoxide dismutase and ascorbate peroxidase to repress the cell death induced by wounding.

Wounding caused by rain, wind, and pathogen may lead plants to onset defense response. Previous studies indicated that mechanical wounding stimulates plants to generate nitric oxide (NO) and hydrogen peroxide (H(2)O(2)). In this study, the functions of NO and H(2)O(2) after wounding in sweet potato (Ipomoea batatas cv. Tainung 57) was further analyzed. Mechanical wounding damaged cells and resulted in necrosis, but the presence of NO donors or NO scavenger might reduce or enhance the cell death caused by wounding, respectively. The amount of H(2)O(2) induced by wounding was also decreased or increased when plants were incubated with NO donors or NO scavenger, individually. These results indicate that NO may regulate H(2)O(2) generation to affect cell death. NO-induced proteins isolated from two-dimensional electrophoresis were identified to be Copper/Zinc superoxide dismutases (CuZnSODs). The activities of CuZnSODs and ascorbate peroxidase (APX) could be enhanced by NO. In addition, the expression of CuZnSOD and APX was induced by wounding via NO, and their expression was further stimulated by NO through the generation of cGMP. The influx of calcium ions and the activity of NADPH oxidase were also involved in the NO signal transduction pathway inducing APX expression. Collectively, the generation of H(2)O(2) in wounded plants might trigger cell death. Meanwhile, the production of NO induced by wounding stimulated signal transducers including cGMP, calcium ions, and H(2)O(2) to activate CuZnSOD and APX, which further decreased H(2)O(2) level and reduced the cell death caused by wounding.

Expression of an Oncidium gene encoding a patatin-like protein delays flowering in Arabidopsis by reducing gibberellin synthesis.

The involvement of lipase in flowering is seldom studied, and this research provides evidence that fatty acids produced by lipase affect flowering. OSAG78 encoding a patatin-like protein was isolated from Oncidium Gower Ramsey. OSAG78 fused with green fluorescent protein was found to localize at the cell membrane. Transgenic Arabidopsis overexpressing OSAG78 demonstrated higher lipase activity than the wild-type control. In addition, the amount of free linoleic acid and linolenic acid in transgenic Arabidopsis was found to be higher than that in the wild type. Transgenics overexpressing OSAG78 exhibited altered phenotypes, including smaller leaves and rounder flowers, and also demonstrated a late flowering phenotype that could be rescued by gibberellin A(3) (GA(3)) application. Several flowering-related genes were analyzed, indicating that the expression of gibberellin-stimulated genes was decreased in the plants overexpressing OSAG78. Also, the expression of AtGA2ox1, AtGA3ox1 and AtGA20ox1 genes encoding GA2-, GA3- and GA20-oxidases, respectively, which are mainly responsible for gibberellin metabolism, was decreased, and the level of GA(4), a bioactive gibberellin, measured by gas chromatography-mass spectrometry was also reduced in the overexpressing lines. Furthermore, the expression levels of AtGA3ox1 and AtGA20ox1 were significantly decreased in wild-type Arabidopsis treated with linoleic acid, linolenic acid or methyl jasmonate. The membrane-bound OSAG78 might hydrolyze phospholipids to release linoleic acid and linolenic acid, and then depress the expression of genes encoding GA3- and GA20-oxidase. These changes reduced the bioactive gibberellin level, and, finally, late flowering occurred. Our results indicate that a patatin-like membrane protein with lipase activity affects flowering through the regulation of gibberellin metabolism.