The MYB transcription factor SmMYB113 directly regulates ethylene-dependent flower abscission in eggplant.

Flower abscission is an important developmental process that can significantly reduce the yield of horticultural plants. We previously reported that SmMYB113 is a key transcription factor promoting anthocyanin biosynthesis and improve fruit quality. However, the overexpression of SmMYB113 in eggplant increased flower drop rate and reduced fruit yield. Here, we elucidate the regulatory mechanisms of SmMYB113 on flower abscission in eggplant. RNA-seq analysis indicated that the regulation of flower abscission by SmMYB113 was associated with altered expression of genes related to ethylene biosynthesis and signal transduction, including ethylene biosynthetic genes SmACS1, SmACS8 and SmACO4. Then, the ethylene content in flowers and the function of ethephon (ETH, which promotes fruit ripening) and 1-Methylcyclopropene (1-MCP, which acts as an ethylene perception inhibitor) were analyzed, which revealed that SmMYB113 directly regulates ethylene-dependent flower abscission. Yeast one-hybrid and dual-luciferase assays revealed that SmMYB113 could directly bind to the promoters of SmACS1, SmACS8, and SmACO4 to activate their expression. Through construction of a yeast two-hybrid (Y2H) screening library, the protein SmERF38 was found to interact with SmMYB113, and verified by Y2H, bimolecular fluorescence complementation (BiFC), and luciferase complementation assay. Furthermore, dual-luciferase assays showed that SmERF38 enhanced the role of SmMYB113 on the promoters of SmACS1. Our results provided new insight into the molecular mechanism of flower abscission in eggplant.

RNA-sequencing analysis reveals novel genes involved in the different peel color formation in eggplant.

Eggplant (Solanum melongena L.) is a highly nutritious vegetable. Here, the molecular mechanism of color formation in eggplants was determined using six eggplant cultivars with different peel colors and two SmMYB113-overexpressing transgenic eggplants with a purple peel and pulp. Significant differentially expressed genes (DEGs) were identified by RNA-sequencing analysis using the following criteria: log2(sample1/sample2) ≥ 0.75 and q-value ≤ 0.05. Two analytical strategies were used to identify genes related to the different peel color according to the peel color, flavonoids content, delphinidins/flavonoids ratio, and the content of anthocyanins. Finally, 27 novel genes were identified to be related to the color difference among eggplant peels and 32 novel genes were identified to be related to anthocyanin biosynthesis and regulated by SmMYB113. Venn analysis revealed that SmCytb5, SmGST, SmMATE, SmASAT3, and SmF3'5'M were shared among both sets of novel genes. Transient expression assay in tobacco suggested that these five genes were not sufficient for inducing anthocyanin biosynthesis alone, but they play important roles in anthocyanin accumulation in eggplant peels. Yeast one-hybrid, electrophoretic mobility shift assay and dual-luciferase assays indicated that the expression of the five genes could be directly activated by SmMYB113 protein. Finally, a regulatory model for the mechanism of color formation in eggplant was proposed. Overall, the results of this study provide useful information that enhances our understanding of the molecular mechanism underlying the different color formation in eggplant.

Sub-wavelength tight-focusing of terahertz waves by polarization-independent high-numerical-aperture dielectric metalens.

A focusing device is one of the key elements for terahertz applications, including homeland security, medicine, industrial inspection, and other fields. Sub-wavelength tight-focusing of terahertz waves is attractive for microscopy and spectroscopy. Flat optical lenses based on metasurfaces have shown potential in diffraction-limit focusing and advantages of ultrathin thickness and lightweight for large-aperture optics. However previously reported THz metalenses suffered from either polarization-dependency or small numerical aperture (NA), which greatly limits their focusing performance. In this paper, to achieve high-NA and polarization-free operation, we proposed a polarization-independent dielectric metasurface with a sub-wavelength period of 0.4λ. A planar terahertz lens based on such metasurface was designed for a wavelength of λ = 118.8 µm with a focal length of 100λ, a radius of 300λ, and a high NA of 0.95, which was fabricated with a silicon-on-insulator wafer. The experimental results demonstrate a tight focal spot with sub-wavelength full widths at half-maxima of 0.45λ and 0.61λ in the x and y directions, respectively, on the focal plane. In the x direction, the size of 0.45λ is even smaller than the diffraction limit 0.526λ (0.5λ/NA). Such a metalens is favorable for sub-wavelength tight-focusing terahertz waves with different polarizations, due to its polarization independence. The metalens has potential applications in THz imaging, spectroscopy, information processing, and communications, among others.

Numerical Study and Optimisation of a Novel Single-Element Dual-Frequency Ultrasound Transducer.

A dual-frequency ultrasound transducer (DFUT) is usually preferred for its numerous advantageous applications, especially in biomedical imaging and sensing. However, most of DFUTs are based on the combination of fundamental and harmonic operations, or integration of multiple different single-frequency ultrasound transducers, hindering perfect beam alignment and acoustic impedance matching. A novel single-element DFUT has been proposed in this paper. A small piezoelectric membrane is used as the high-frequency ultrasound transducer, which is stacked on a large non-piezoelectric elastic membrane with a groove used as the low-frequency capacitive ultrasound transducer. Such a capacitive-piezoelectric hybrid structure is theoretically analysed in details, based on the electrostatic attraction force and converse piezoelectric effect. Both the low and high resonance frequencies are independently derived, with a maximum deviation of less than 4% from the finite element simulations. Besides, a lumped-parameter equivalent circuit model of combining both the capacitive and piezoelectric ultrasound transducers was also described. Based on our dual-frequency structure design, a high-to-low frequency ratio of about 2 to more than 20 could be achieved, with easy and independent controllability of two frequencies, and the high-frequency operation shows at least an order-of-magnitude displacement sensitivity improvement compared with the conventional harmonic operations.

Planar binary-phase lens for super-oscillatory optical hollow needles.

Optical hollow beams are suitable for materials processing, optical micromanipulation, microscopy, and optical lithography. However, conventional optical hollow beams are diffraction-limited. The generation of sub-wavelength optical hollow beams using a high numerical aperture objective lens and pupil filters has been theoretically proposed. Although sub-diffraction hollow spot has been reported, nondiffracting hollow beams of sub-diffraction transverse dimensions have not yet been experimentally demonstrated. Here, a planar lens based on binary-phase modulation is proposed to overcome these constraints. The lens has an ultra-long focal length of 300λ. An azimuthally polarized optical hollow needle is experimentally demonstrated with a super-oscillatory transverse size (less than 0.38λ/NA) of 0.34λ to 0.42λ, where λ is the working wavelength and NA is the lens numerical aperture, and a large depth of focus of 6.5λ. For a sub-diffraction transverse size of 0.34λ to 0.52λ, the nondiffracting propagation distance of the proposed optical hollow needle is greater than 10λ. Numerical simulation also reveals a good penetrability of the proposed optical hollow needle at an air-water interface, where the needle propagates through water with a doubled propagation distance and without loss of its super-oscillatory property. The proposed lens is suitable for nanofabrication, optical nanomanipulation, super-resolution imaging, and nanolithography applications.

Creation of Sub-diffraction Longitudinally Polarized Spot by Focusing Radially Polarized Light with Binary Phase Lens.

The generation of a sub-diffraction longitudinally polarized spot is of great interest in various applications, such as optical tweezers, super-resolution microscopy, high-resolution Raman spectroscopy, and high-density optical data storage. Many theoretical investigations have been conducted into the tight focusing of a longitudinally polarized spot with high-numerical-aperture aplanatic lenses in combination with optical filters. Optical super-oscillation provides a new approach to focusing light beyond the diffraction limit. Here, we propose a planar binary phase lens and experimentally demonstrate the generation of a longitudinally polarized sub-diffraction focal spot by focusing radially polarized light. The lens has a numerical aperture of 0.93 and a long focal length of 200λ for wavelength λ = 632.8 nm, and the generated focal spot has a full-width-at-half-maximum of about 0.456λ, which is smaller than the diffraction limit, 0.54λ. A 5λ-long longitudinally polarized optical needle with sub-diffraction size is also observed near the designed focal point.

Generation of a sub-diffraction hollow ring by shaping an azimuthally polarized wave.

The generation of a sub-diffraction optical hollow ring is of great interest in various applications, such as optical microscopy, optical tweezers, and nanolithography. Azimuthally polarized light is a good candidate for creating an optical hollow ring structure. Various of methods have been proposed theoretically for generation of sub-wavelength hollow ring by focusing azimuthally polarized light, but without experimental demonstrations, especially for sub-diffraction focusing. Super-oscillation is a promising approach for shaping sub-diffraction optical focusing. In this paper, a planar sub-diffraction diffractive lens is proposed, which has an ultra-long focal length of 600 λ and small numerical aperture of 0.64. A sub-diffraction hollow ring is experimentally created by shaping an azimuthally polarized wave. The full-width-at-half-maximum of the hollow ring is 0.61 λ, which is smaller than the lens diffraction limit 0.78 λ, and the observed largest sidelobe intensity is only 10% of the peak intensity.

Super-oscillatory focusing of circularly polarized light by ultra-long focal length planar lens based on binary amplitude-phase modulation.

In traditional optics, the focal spot size of a conventional lens is restricted to the diffraction limit 0.5λ/NA, where λ is the wavelength in vacuum and NA is the numerical aperture of the lens. Recently, various sub-diffraction focusing optical devices have been demonstrated, but they usually have short focal length and high numerical aperture. Moreover, they always suffer the problem of huge sidelobes near the focal spot and small field of view, especially when the focal spot size is less than the super-oscillation criteria 0.38λ/NA. To address the problem, here, we reported a far-field sub-diffraction point-focusing lens based on binary phase and amplitude modulation with ultra-long focal length 252.8 µm (399.5λ) and small numerical aperture 0.78, and experimentally demonstrated a super-oscillatory focusing of circularly polarized light with spot size 287 nm (0.454λ), smaller than the diffraction limit 0.64λ and the super-oscillation criterion 0.487λ. What's more, on the focal plane, in the measured area within the radius of 142λ, the largest sidelobe intensity is less than 26% of the central lobe intensity. Such ultra-long distance super-oscillatory focusing with small sidelobes and large field of view has great potential applications in far-field super-resolution microscopy, ultra-high-density optical storage and nano-fabrication.