The MYB transcription factors and plant hormone ABA have been suggested to play a role in fruit anthocyanin biosynthesis, but supporting genetic evidence has been lacking in sweet cherry. The present study describes the first functional characterization of an R2R3-MYB transcription factor, PacMYBA, from red-colored sweet cherry cv. Hong Deng (Prunus avium L.). Transient promoter assays demonstrated that PacMYBA physically interacted with several anthocyanin-related basic helix-loop-helix (bHLH) transcription factors to activate the promoters of PacDFR, PacANS and PacUFGT, which are thought to be involved in anthocyanin biosynthesis. Furthermore, the immature seeds of transgenic Arabidopsis plants overexpressing PacMYBA exhibited ectopic pigmentation. Silencing of PacMYBA, using a Tobacco rattle virus (TRV)-induced gene silencing technique, resulted in sweet cherry fruit that lacked red pigment. ABA treatment significantly induced anthocyanin accumulation, while treatment with the ABA biosynthesis inhibitor nordihydroguaiaretic acid (NDGA) blocked anthocyanin production. PacMYBA expression peaked after 2 h of pre-incubation in ABA and was 15.2-fold higher than that of sweet cherries treated with NDGA. The colorless phenotype was also observed in the fruits silenced in PacNCED1, which encodes a key enzyme in the ABA biosynthesis pathway. The endogenous ABA content as well as the transcript levels of six structural genes and PacMYBA in PacNCED1-RNAi (RNA interference) fruit were significantly lower than in the TRV vector control fruit. These results suggest that PacMYBA plays an important role in ABA-regulated anthocyanin biosynthesis and ABA is a signal molecule that promotes red-colored sweet cherry fruit accumulating anthocyanin.

A new spectrometric method ultra performance liquid chromatography-tandem mass spectrometric with high precision and rapid analysis was developed to separate 17 phenolic compounds. Different species of cherries, including 10 sweet cherry (Prunus avium L.) cultivars, a tart cherry (P. cerasus L.) rootstock (CAB), and a hybrid rootstock 'Colt' (P. avium × P. pseudocerasus), were analyzed for phenolics contents by this method. The results showed that significant differences were observed among the phenolic compound contents in different cherry species. In 10 sweet cherry cultivars, the contents of neochlorogenic acid and cyanidin-3O-rutinoside were much higher in red-colored fruits (for example, 64.60 and 44.50 mg/100 g fresh weight in Burlat, respectively) than those in bicolored ones. Principal component analysis revealed that cyanidin-3O-rutinoside was an effective index for grouping the cultivars with similar species and fruit colors. Moreover, there were strong positive correlations between phenolics content and antioxidant activity, which was higher in red-colored cherries.

SummarySweet cherry is a diploid tree species and its fruit skin has rich colours from yellow to blush to dark red. The colour is closely related to anthocyanin biosynthesis and is mainly regulated at the transcriptional level by transcription factors that regulate the expression of multiple structural genes. However, the genetic and molecular bases of how these genes ultimately determine the fruit skin colour traits remain poorly understood. Here, our genetic and molecular evidences identified the R2R3 MYB transcription factor PavMYB10.1 that is involved in anthocyanin biosynthesis pathway and determines fruit skin colour in sweet cherry. Interestingly, we identified three functional alleles of the gene causally leading to the different colours at mature stage. Meanwhile, our experimental results of yeast two‐hybrid assays and chromatin immunoprecipitation assays revealed that PavMYB10.1 might interact with proteins PavbHLH and PavWD40, and bind to the promoter regions of the anthocyanin biosynthesis genes PavANS and PavUFGT; these findings provided to a certain extent mechanistic insight into the gene's functions. Additionally, genetic and molecular evidences confirmed that PavMYB10.1 is a reliable DNA molecular marker to select fruit skin colour in sweet cherry.

A cross between the sweet cherry (Prunus avium) cultivars ‘Wanhongzhu’ and ‘Lapins’ was performed to create a mapping population suitable for the construction of a linkage map. The specific-locus amplified fragment (SLAF) sequencing technique used as a single nucleotide polymorphism (SNP) discovery platform and generated 701 informative genotypic assays; these, along with 16 microsatellites (SSRs) and the incompatibility (S) gene, were used to build a map which comprised 8 linkage groups (LGs) and covered a genetic distance of 849.0 cM. The mean inter-marker distance was 1.18 cM and there were few gaps > 5 cM in length. Marker collinearity was maintained with the established peach genomic sequence. The map was used to show that trunk diameter (TD) is under the control of 4 loci, mapping to 3 different LGs. Different locus influenced TD at a varying stage of the tree’s development. The high density ‘W×L’ genetic linkage map has the potential to enable high-resolution identification of QTLs of agronomically relevant traits, and accelerate sweet cherry breeding.

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The terahertz band is an increasingly important spectrum in a wide range of applications from bioimaging and medical diagnostics to security and wireless communications. We propose a tunable terahertz coherent radiation source based on graphene plasmon-induced transition radiation. The transition radiation in terahertz regime arises from the graphene plasmons, which are excited by a normally incident bunched electron beam. We analyze the field-intensities and spectral-angular distributions of the transition radiation with respect to Fermi energy, substrate dielectric permittivity, and electron bunch energy for both the coherent and incoherent radiation. The effect of electron bunching on the radiation pattern is discussed. The mechanism of plasmon frequency-selective transition radiation is discovered.

An extended interaction oscillator (EIO) generating Terahertz (THz) wave is presented by theoretical study and simulation study in this paper. A rectangular reentrant coupled-cavity is proposed as its slow-wave structure (SWS). The equivalent circuit method (ECM) is adopted to calculate the dispersion relation and circuit parameters of the SWS. The beam-wave interaction of the EIO is theoretically studied in detail, including the beam loading conductance, the conversion efficiency and the optimal gap number. The dependence is investigated of the beam loading conductance and the conversion efficiency on the gap number and the beam velocity. Some properties of the cold circuit are simulated by CST software, including the dispersion relation and the filed distribution. These simulation results agree well with those of ECM. The operating mode of EIO is chosen very close to the βL=2π point with corresponding frequency about 0.225 THz, when the beam voltage is 13 kV, the current 105 mA, the cavity was designed with the period 0.3 mm, 14-gap, the height 1.6 mm and the width 0.76 mm. Simulation results of beam-wave interaction with PIC codes show that the excited frequency is 0.225 THz and peak output power 44 W.

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