Improving temperature characteristics of GaN-based ultraviolet laser diodes by using InGaN/AlGaN quantum wells.

Temperature characteristics of GaN-based laser diodes are investigated. It is noted that the characteristic temperature of the threshold current (T0) decreases with decreasing lasing wavelength for GaN-based LDs. The performance deteriorates seriously for UV LDs at high temperature. It is ascribed to the increase of carriers escaping from quantum wells due to the lower potential barrier height. In this Letter, AlGaN is used as the barrier layer in UV LDs instead of GaN to improve the temperature characteristic of the threshold current and slope efficiency by increasing the potential barrier height of quantum wells. Based on this structure, a high output power of 4.6 W is obtained at the injection current of 3.8 A; its lasing wavelength is 386.8 nm.

Transcriptome analysis reveals the effect of acidic environment on adventitious root differentiation in Camellia sinensis.

The generation of adventitious roots (ARs) is the key to the success of cuttings. The appropriate environment for AR differentiation in tea plants is acidic. However, the mechanism is unclear. In this study, pH 4.5 was suitable condition for the differentiation of AR in tea plants. At the base of cuttings, the root primordia differentiated ARs more rapidly at pH 4.5 than pH 7.0, and nine AR differentiation-related genes were found to be differentially expressed in 30 days, the result was also validated by qRT-PCR. The promoter regions of these genes contained auxin and brassinosteroid response elements. The expression levels of several genes which were involved in auxin and brassinosteroid synthesis as well as signaling at pH 4.5 compared to pH 7.0 occurred differential expression. Brassinolide (BL) and indole-3-acetic acid (IAA) could affect the differentiation of ARs under pH 4.5 and pH 7.0. By qRT-PCR analysis of genes during ARs generation, BL and IAA inhibited and promoted the expression of CsIAA14 gene, respectively, to regulate auxin signal transduction. Meanwhile, the expression levels of CsKNAT4, CsNAC2, CsNAC100, CsWRKY30 and CsLBD18 genes were up-regulated upon auxin treatment and were positively correlated with ARs differentiation.This study showed that pH 4.5 was the most suitable environment for the root primordia differentiation of AR in tea plant. Proper acidic pH conditions promoted auxin synthesis and signal transduction. The auxin initiated the expression of AR differentiation-related genes, and promoted its differentiated. BL was involved in ARs formation and elongation by regulating auxin signal transduction.

Transcriptomic Analysis of Yunwu Tribute Tea Leaves under Cold Stress.

Background: Cold stress usually occurs in winter and is one of the most significant environmental factors restricting the growth of the tea plant as well as its geographical distribution. Objective: It is necessary to identify the physiological and molecular mechanisms of plants under cold stress so that cold-tolerant crop varieties can be cultivated to limit production losses. At the same time, this would allow the crop planting area to be expanded, hence improving the economic benefits. Methods: In this study, the transcriptome data of Yunwu Tribute Tea under cold conditions were obtained using the Illumina HiSeq platform. By analyzing changes in transcriptome data associated with the antioxidant enzyme system, plant hormone signal transduction, proline and tyrosine metabolism pathways, and transcription factors, the molecular mechanisms involved in Yunwu Tribute Tea under cold stress were investigated. Results: In this study, Illumina HiSeq technology was applied to investigate the cold-tolerance mechanism. For this purpose, cDNA libraries were obtained from two groups of samples, namely the cold-treated group (DW) and the control group (CK). A total of 185,973 unigenes were produced from 511,987 assembled transcripts; among these, 16,020 differentially expressed genes (DEGs) (corrected p-value < 0.01, |log2(fold change)| >3), including 9606 up-regulated and 6414 down-regulated genes, were obtained. Moreover, the antioxidant enzyme system, plant hormone signal transduction, proline and tyrosine metabolism pathways, and transcription factors were analyzed; based on these results, a series of candidate genes related to cold stress were screened out and discussed. The physiological indexes related to the low-temperature response were tested, along with five DEGs which were validated by quantitative real-time PCR. Conclusions: Differential gene expression analysis has confirmed that substantial cold-responsive genes are related to the antioxidant enzyme system, plant hormone signal transduction, proline metabolism pathway, tyrosine metabolism pathway, and transcription factors.

Transcriptome analysis reveals the effect of grafting on gossypol biosynthesis and gland formation in cotton.

BACKGROUND: Gossypol is a unique secondary metabolite and sesquiterpene in cotton, which is mainly synthesized in the root system of cotton and exhibits many biological activities. Previous research found that grafting affected the density of pigment glands and the gossypol content in cotton. RESULTS: This study performed a transcriptome analysis on cotton rootstocks and scions of four grafting methods. The gene expression of mutual grafting and self-grafting was compared to explore the potential genes involved in gossypol biosynthesis. A total of six differentially expressed enzymes were found in the main pathway of gossypol synthesis-sesquiterpene and triterpene biosynthesis (map00909): lupeol synthase (LUP1, EC:5.4.99.41), beta-amyrin synthase (LUP2, EC:5.4.99.39), squalene monooxygenase (SQLE, EC:1.14.14.17), squalene synthase (FDFT1, EC:2.5.1.21), (-)-germacrene D synthase (GERD, EC:4.2.3.75), ( +)-delta-cadinene synthase (CADS, EC:4.2.3.13). By comparing the results of the gossypol content and the density of the pigment gland, we speculated that these six enzymes might affect the biosynthesis of gossypol. It was verified by qRT-PCR analysis that grafting could influence gene expression of scion and stock. After suppressing the expression of the LUP1, FDFT1, and CAD genes by VIGS technology, the gossypol content in plants was significantly down-regulated. CONCLUSIONS: These results indicate the potential molecular mechanism of gossypol synthesis during the grafting process and provide a theoretical foundation for further research on gossypol biosynthesis.

Low threshold current density and high power InGaN-based blue-violet laser diode with an asymmetric waveguide structure.

Performance of InGaN-based blue-violet laser diodes (LD) with different waveguide structure were investigated by simulation and experimental methods. Theoretical calculation demonstrated that threshold current (Ith) can be reduced and slope efficiency (SE) can be improved by using an asymmetric waveguide structure. Based on the simulation results, a LD with 80-nm-thick In0.03Ga0.97N lower waveguide (LWG) and 80-nm-thick GaN upper waveguide (UWG) is fabricated with flip chip package. Under continuous wave (CW) current injection at room temperature, its optical output power (OOP) reaches 4.5 W at an operating current of 3 A and the lasing wavelength of 403 nm. The threshold current density (Jth) is 0.97 kA/cm2 and the SE is about 1.9 W/A.

Influence of growth interruption on the morphology and luminescence properties of AlGaN/GaN ultraviolet multi-quantum wells.

The influence of growth interruption on the surface and luminescence properties of AlGaN/GaN ultraviolet multi-quantum wells (UV MQWs) is investigated. It is found that when the well and barrier layers of MQW samples are continuously grown at the same temperature, they have lower edge dislocation density and flatter surface of MQWs compared to samples with interrupted well and barrier growth. Moreover, continuous growth of well and barrier layers is more conducive to improving the luminescence efficiency of MQWs. This phenomenon is attributed to more impurity incorporation induced by the growth interruption, while a continuous growth of well and barrier can reduce surface diffusion and migration processes of atoms, reducing the defects and surface roughness of MQWs. In addition, the continuous growth of well and barrier can better control the reaction between Al and N atoms, avoiding the formation of excessively high Al content AlGaN at the well/barrier interface, thus improving the luminescence of UV MQWs.

Confirmation of 'Pollen- and Seed-Specific Gene Deletor' System Efficiency for Transgene Excision from Transgenic Nicotiana tabacum under Field Conditions.

The commercial application of genetically modified plants has been seriously impeded by public concern surrounding the potential risks posed by such plants to the ecosystem and human health. Previously, we have developed a 'pollen- and seed-specific Gene Deletor' system that automatically excised all transgenes from the pollen and seeds of greenhouse-grown transgenic Nicotiana tabacum. In this study, we conducted seven field experiments over three consecutive years to evaluate the stability of transgene excision under field conditions. Our results showed that transgenes were stably excised from transgenic Nicotiana tabacum under field conditions with 100% efficiency. The stability of transgene excision was confirmed based on PCR, as well as the GUS staining patterns of various organs (roots, leaves, petiole, stem, flower, fruit, and seeds) from transgenic N. tabacum. In six transgenic lines (D4, D10, D31, D56, and D43), the transgenes were stably deleted in the T0 and T1 generations. Thus, the 'Gene Deletor' system is an efficient and reliable method to reduce pollen- and seed-mediated unintentional gene flow. This system might help to alleviate the food safety concerns associated with transgenic crops.

Haploid induction in allotetraploid tobacco using DMPs mutation.

MAIN CONCLUSION: dmp1dmp2dmp3 mutants created by CRISPR/Cas9 could trigger maternal haploids in the allotetraploid model plant Nicotiana tabacum L. Double haploid (DH) technology is becoming increasingly important because it can significantly accelerate the breeding process. Haploid induction plays a fundamental role in the production of DH lines. Haploid induction has been realized and applied in diploid plants using DMP genes. However, it has yet to be elucidated whether haploid induction could be established in polyploid plants. In the current study, three homologues of the DMP genes (NtDMP1, 2, and 3) were identified in the allotetraploid plant Nicotiana tabacum, and the encoded proteins localized in the endoplasmic reticulum. Loss-of-function mutations in all three genes triggered maternal haploids with an induction rate of 1.52-1.75%. Compared with wild-type tobacco, the created haploid inducer exhibited differences in pollen vigor and seed germination rate. Furthermore, to rapidly and easily screen haploids, a visible haploid identification system was established based on a powdery mildew resistance phenotype. Findings from this study lay the foundation for the potential application of haploid inducers in allotetraploid plants such as tobacco.

Lower threshold current density of GaN-based blue laser diodes by suppressing the nonradiative recombination in a multiple quantum well.

The influence of the nonradiative recombination in a multiple quantum well of GaN-based blue laser diodes (LDs) has been are studied experimentally and theoretically by analyzing the optical and electrical properties of LDs with various thickness and indium content of quantum wells (QWs). It is found that when keeping the LD emission wavelength nearly unchanged, the LD device performance with thinner QW and higher indium content of InGaN QWs is much better than the LD with thicker QW and lower indium content, having smaller threshold current density, higher output optical power and larger slope efficiency. Typically, the threshold current density is as low as 0.69 kA/cm2, and the corresponding threshold current is only 250 mA. The lifetime is more than 10,000 hours at a fixed injection current of 1.2 A under a room-temperature continuous-wave operation. Characteristics of photoluminescence (PL) microscopy images, temperature dependent PL spectra, time-resolved PL and electroluminescence spectra demonstrate that a reduction of the nonradiative recombination centers and an improvement of homogeneity in QWs are the main reason for the performance improvement of GaN-based LD using thinner QW layers with a higher indium content in a certain range. Moreover, theoretical calculation results demonstrate that using a thinner quantum well is also helpful for improving the device performance if the change of alloy material quality is considered during the calculation.

Transient behavior of AlGaN photoluminescence induced by carbon-related defect reactions.

We have observed the transient behavior in the AlGaN photoluminescence. Under an excitation of 325 nm He-Cd laser beam, the blue luminescence (BL) bands and yellow luminescence (YL) bands of AlGaN vary with increasing illumination time. We propose that the chemical reactions between BL-related CNON-Hi (CN-Hi) and YL-related CN-Hi (CN) defect states are the cause of such a phenomenon. The BL transition temperature (Tt) is defined as the temperature at which the intensity of BL bands induced by CNON-Hi is equal to that originated from CN-Hi. Only at Tt, BL shows a peak energy variation due to the exposure. The Tt of AlGaN is higher than what is similarly detected in GaN because of the high reactivity of Al to O.

Improved performance of GaN-based blue laser diodes using asymmetric multiple quantum wells without the first quantum barrier layer.

An asymmetric multiple quantum well (MQW) without the first quantum barrier layer is designed, and its effect on the device performance of GaN-based blue LDs has been studied experimentally and theoretically. It is found that compared with LD using symmetrical multiple quantum well, device performance is improved significantly by using asymmetric MQW, i.e. having a smaller threshold current density, a higher output optical power and a larger slope efficiency. The threshold current density decreases from 1.28 kA/cm2 to 0.86 kA/cm2, meanwhile, the optical power increases from 1.77 W to 2.52 W, and the slope efficiency increases from 1.15 W/A to 1.49 W/A. The electroluminescence characteristics below the threshold current demonstrate that asymmetric MQW is more homogeneous due to the suppressed strain and piezoelectric field. Furthermore, theoretical calculation demonstrates that the enhancement of electron injection ratio and reduction in optical loss are another reason for the improvement of device performance, which is attributed to a smaller electron potential barrier and a more concentrated optical field distribution in the asymmetric structure, respectively. The new structure design with asymmetric MQW is concise for epitaxial growth, and it would also be a good possible choice for GaN-based LDs with other lasing wavelengths.

Intermedial annealing process applied during the growth of quantum wells and its influence on the performance of GaN-based laser diodes.

An intermedial annealing treatment is adopted during epitaxial growth of InGaN/GaN multiple quantum well (MQW) by the metal-organic chemical vapor deposition (MOCVD), which is employed after each GaN cap layer growth is finished. Optical power, threshold current and slope efficiency of GaN-based laser diodes is improved through an appropriate intermedial annealing process. A further investigation about the influence of annealing duration on the luminescence characteristics of light-emitting diodes and the surface topography evolution of single quantum well layers is conducted through the study of electroluminescence, temperature dependent photoluminescence and atomic force microscopy. It is found that the improvement of GaN-based laser diode is attributed to reduction of nonradiative recombination centers in MQW, which is due to a better interface quality between well and barrier layers after an intermedial annealing process.

Room temperature continuous-wave operated 2.0-W GaN-based ultraviolet laser diodes.

Temperature characteristics of near-UV laser diodes (LDs) with a lasing wavelength of 384 nm are investigated. The characteristic temperature of threshold current (T0) of the UV LDs is low. Thus, the performance of the UV LDs under continuous wave (CW) operation is not as good as under pulsed operation especially at a high injection current. In addition, it is found that self-heating is a key factor for CW characteristics of the UV LDs, where suppression of the self-heating by using thick waveguide layers can increase the critical current of thermal rollover of the UV LD's operation. A high CW output power of 2.0 W is achieved for an InGaN near-UV LD with the n-side down on a sub-mount, whose threshold current density is 1.27 kA/cm2 and the highest wall plug efficiency (WPE) is approximately 15.9% at an injection current of 1.2 A.

Identification of a novel laccase gene EuLAC1 and its potential resistance against Botrytis cinerea.

In this study, a novel laccase gene, EuLAC1, was cloned from Eucommia ulmoides Oliver (E. ulmoides). An overexpression vector harboring the EuLAC1 was constructed and introduced into the tobacco (Nicotiana tabacum cv. Xanthi). The laccase activity, resistance to Botrytis cinerea (B. cinerea) and lignin level in wild-type and transgenic plants were thereafter investigated. Interestingly, the transgenic tobacco displayed a significantly higher laccase activity and resistance to gray mold as compared to the wild-type tobacco. Additionally, the lignin contents in the leaves and stems of the transgenic tobacco were significantly higher in comparison to the wild-type tobacco. Scanning electron microscopy was used to observe the cross sections of wild-type and transgenic tobacco stems and it was noted that the cell wall near the xylem catheter of the transgenic tobacco was substantially thicker and the outline clearer than that of the wild-type. Thus, the EuLAC1 gene can significantly increase laccase activity and lignin content in tobacco, leading to an increase in the physical defenses, thereby increasing tobacco resistance to gray mold.

Effect of Shading on the Morphological, Physiological, and Biochemical Characteristics as Well as the Transcriptome of Matcha Green Tea.

High-quality tea leaves are required for matcha production. Shading is one of the key agronomic practices that can increase the quality of green tea. The objectives among matcha tea producers include increasing the ammonia and chlorophyll contents of tea buds, decreasing tea polyphenol contents, and enhancing tea aroma formation. In this study, Fuding white tea plants were cultivated under open-air conditions (control) as well as under 85% (S85) and 95% (S95) shade. The chlorophyll contents were highest for the S85 treatment, followed by the S95 and control treatments. Moreover, shading increased the theanine and caffeine contents, while decreasing the polyphenol (epicatechin and epigallocatechin) contents, thereby optimizing matcha tea flavors. A total of 2788 differentially expressed genes (DEGs) were identified, of which 1151 and 1637 were respectively upregulated and downregulated in response to shading. The GO and KEGG enrichment analyses indicated that most of the DEGs were associated with metabolic processes (e.g., MAPK signaling, plant-pathogen interactions, and phenylpropanoid biosynthesis). Therefore, shading may modulate tea plant metabolism, signaling, biosynthetic activities, and environment-related changes to gene transcription. The expression of amino acid permeases (APP) encoding genes was downregulated in tea plants. Thus, shading influences theanine biosynthesis and the AAP-mediated distribution of theanine in tea plants.

Overexpression of the Eucommia~ulmoides Aquaporin, EuPIP1;1, Promotes Leaf Growth, Flowering and Bolting, and Stress Tolerance in Arabidopsis.

Plasma membrane intrinsic protein (PIP) is one of the largest subfamilies of Aquaporins (AQPs) and plays an important role in plant growth and development, and resistance to abiotic stress. In this study, the full length of the EuPIP1;1 cDNA was cloned from Eucommia ulmoides using the rapid amplification of cDNA ends (RACE) method. The EuPIP1;1 gene was induced by drought treatment and expressed in all tested tissues, with the highest expression level in fruit. The subcellular localization showed that EuPIP1;1 was located in the plasma membrane. Constitutive overexpression of EuPIP1;1 in Arabidopsisthaliana could promote leaf growth and development, and accelerate bolting and flowering. Six genes related to growth and flowering (AtPIF4, AtTCP14, AtCRY1, AtCRY2, AtFCA and AtFT) were significantly up-regulated in transgenic lines. Further, EuPIP1;1 gene improved resistance to drought and salt stress in transgenic Arabidopsis. Under drought and salt stress treatment, the transgenic lines had a higher germination rate and accumulation of osmotic substances, lower membrane damage, and could maintain ion homeostasis. Our results suggest that EuPIP1;1 plays an essential role in plant growth and development and in the response to drought and salt stress.

BRITTLE CULM17, a Novel Allele of TAC4, Affects the Mechanical Properties of Rice Plants.

Lodging resistance of rice (Oryza sativa L.) has always been a hot issue in agricultural production. A brittle stem mutant, osbc17, was identified by screening an EMS (Ethylmethane sulfonate) mutant library established in our laboratory. The stem segments and leaves of the mutant were obviously brittle and fragile, with low mechanical strength. Examination of paraffin sections of flag leaf and internode samples indicated that the number of cell layers in mechanical tissue of the mutant was decreased compared with the wild type, Pingtangheinuo, and scanning electron microscopy revealed that the mechanical tissue cell walls of the mutant were thinner. Lignin contents of the internodes of mature-stage rice were significantly lower in the mutant than in the wild type. By the MutMap method, we found candidate gene OsBC17, which was located on rice chromosome 2 and had a 2433 bp long coding sequence encoding a protein sequence of 810 amino acid residues with unknown function. According to LC-MS/MS analysis of intermediate products of the lignin synthesis pathway, the accumulation of caffeyl alcohol in the osbc17 mutant was significantly higher than in Pingtangheinuo. Caffeyl alcohol can be polymerized to the catechyl lignin monomer by laccase ChLAC8; however, ChLAC8 and OsBC17 are not homologous proteins, which suggests that the osbc17 gene is involved in this process by regulating laccase expression.

Transcriptome analysis of scions grafted to potato rootstock for improving late blight resistance.

BACKGROUND: Late blight seriously threatens potato cultivation worldwide. The severe and widespread damage caused by the fungal pathogen can lead to drastic decreases in potato yield. Although grafting technology has been widely used to improve crop resistance, the effects of grafting on potato late blight resistance as well as the associated molecular mechanisms remain unclear. Therefore, we performed RNA transcriptome sequencing analysis and the late blight resistance testing of the scion when the potato late blight-resistant variety Qingshu 9 and the susceptible variety Favorita were used as the rootstock and scion, respectively, and vice versa. The objective of this study was to evaluate the influence of the rootstock on scion disease resistance and to clarify the related molecular mechanisms. RESULTS: A Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis revealed that the expression levels of genes related to plant-pathogen interactions, plant mitogen-activated protein kinase (MAPK) signaling pathways, and plant hormone signal transduction pathways were significantly up-regulated in the scion when Qingshu 9 was used as the rootstock. Some of these genes encoded calcium-dependent protein kinases (CDPKs), chitin elicitor receptor kinases (CERKs), LRR receptor serine/threonine protein kinases (LRR-LRKs), NPR family proteins in the salicylic acid synthesis pathway, and MAPKs which were potato late blight response proteins. When Favorita was used as the rootstock, only a few genes of late blight response genes were upregulated in the scion of Qingshu 9. Grafted plants using resistant variety as rootstocks inoculated with P. infestans spores showed significant reductions in lesion size while no significant difference in lesion size was observed when susceptible variety was used as the rootstock. We also showed that this induction of disease resistance in scions, especially scions derived from susceptible potato varieties was mediated by the up-regulation of expression of genes involved in plant disease resistance in scions. CONCLUSIONS: Our results showed that potato grafting using late blight resistant varieties as rootstocks could render or enhance resistance to late blight in scions derived from susceptible varieties via up-regulating the expression of disease resistant genes in scions. The results provide the basis for exploring the molecular mechanism underlying the effects of rootstocks on scion disease resistance.

Stepped upper waveguide layer for higher hole injection efficiency in GaN-based laser diodes.

We propose a stepped upper waveguide layer (UWG) to improve the hole injection efficiency of GaN-based laser diodes (LDs), and investigate its effect on the performance of LDs from experiments and theoretical calculations. The experimental characterization of the LD with stepped UWG presents a decrease of 16.6% for the threshold current as well as an increase of 41.2% for the slope efficiency compared to the LD with conventional GaN UWG. Meanwhile, strong localized effects are found in the quantum wells of LD with stepped UWG and a large blue-shift in the electroluminescence (EL) spectra below the threshold by analyzing the differential efficiency and the EL spectra. The large blue shift implies a stronger polarization field in the LDs, which may affect the injection of holes. Additionally, the simulation results demonstrate that the LD with stepped UWG achieves higher hole injection efficiency by modulating the valence band, and the hole current density injected into the quantum wells reaches 6067 A/cm2.

Transient behaviours of yellow and blue luminescence bands in unintentionally doped GaN.

Yellow Luminescence (YL) band and blue luminescence (BL) band in a studied unintentionally doped GaN sample show a transient behaviour where the observed luminescence intensities change with the exposure time of the sample under 325 nm laser beam excitation at 10-300 K. Such an intensity variation is accompanied with a red-shift for YL peak at 10-140 K and one for BL peak at 140 K. We propose that such behaviours are related to the chemical transformations of YL-related CN and CNON defects, and BL-related CN-Hi and CNON-Hi defects during the exposure.