Demonstration of Ultra-High-Q Silicon Microring Resonators for Nonlinear Integrated Photonics.

A reflowing photoresist and oxidation smoothing process is used to fabricate ultra-high-Q silicon microring resonators based on multimode rib waveguides. Over a wide range of wavelengths near 1550 nm, the average Q-factor of a ring with 1.2-µm-wide waveguides reaches up to 1.17 × 106, with a waveguide loss of approximately 0.28 dB/cm. For a resonator with 1.5-µm-wide waveguides, the average Q-factor reaches 1.20 × 106, and the waveguide loss is 0.27 dB/cm. Moreover, we theoretically and experimentally show that a reduction in the waveguide loss significantly improves the conversion efficiency of four-wave mixing. A high four-wave mixing conversion efficiency of -17.0 dB is achieved at a pump power of 6.50 dBm.

Integrated photonic devices enabled by silicon traveling wave-like Fabry-Perot resonators.

Integrated photonic devices play a key role in modern optical communications, of which optical resonators are important fundamental structures. This work proposes and experimentally demonstrates compact integrated photonic devices based on a traveling wave-like Fabry-Perot (TW-like FP) resonator(s) coupled with waveguides. Add-drop filters based on a single TW-like FP resonator have been realized with a high drop efficiency and the same output direction for the through and drop ports. Particularly, their transmission response can be either symmetric Lorentzian or asymmetric Fano line shape, through adjusting the shift between the two bus waveguides and the waveguide widths. Fano resonance has been demonstrated in a TW-like FP resonator with a very high extinction ratio and large slope rate. The second-order optical filter exhibits low-loss flat-top passbands with small ripples. Owing to the compact size, easy scalability, and large flexibility, TW-like FP cavity-based devices using Fano and Lorentzian resonances will provide new potential applications in integrated photonics.

Light-Response Bric-A-Brack/Tramtrack/Broad proteins mediate cryptochrome 2 degradation in response to low ambient temperature.

Cryptochromes (crys) are photolyase-like blue-light receptors first discovered in Arabidopsis thaliana and later identified in all major evolutionary lineages. Crys are involved in not only blue light responses but also in temperature responses; however, whether and how cry protein stability is regulated by temperature remains unknown. Here, we show that cry2 protein abundance is modulated by ambient temperature and cry2 protein is degraded under low ambient temperature via the 26S proteasome. Consistent with this, cry2 shows high levels of ubiquitination under low ambient temperatures. Interestingly, cry2 degradation at low ambient temperatures occurs only under blue light and not under red light or dark conditions, indicating blue-light-dependent degradation of cry2 at low ambient temperature. Furthermore, low ambient temperature promotes physical interaction of Light-Response Bric-a-Brack/Tramtrack/Broad (LRB) proteins with cry2 to modulate its ubiquitination and protein stability in response to ambient temperature. LRBs promote high-temperature-induced hypocotyl elongation by modulating the protein stability of cry2 protein. These results indicate that cry2 accumulation is regulated by not only blue light but also ambient temperature, and LRBs are responsible for cry2 degradation at low ambient temperature. The stabilization of cry2 by high temperature makes cry2 a better negative regulator of temperature responses.

Truncation of a mannanase from Trichoderma harzianum improves its enzymatic properties and expression efficiency in Trichoderma reesei.

To obtain high expression efficiency of a mannanase gene, ThMan5A, cloned from Trichoderma harzianum MGQ2, both the full-length gene and a truncated gene (ThMan5AΔCBM) that contains only the catalytic domain, were expressed in Trichoderma reesei QM9414 using the strong constitutive promoter of the gene encoding pyruvate decarboxylase (pdc), and purified to homogeneity, respectively. We found that truncation of the gene improved its expression efficiency as well as the enzymatic properties of the encoded protein. The recombinant strain expressing ThMan5AΔCBM produced 2,460 ± 45.1 U/ml of mannanase activity in the culture supernatant; 2.3-fold higher than when expressing the full-length ThMan5A gene. In addition, the truncated mannanase had superior thermostability compared with the full-length enzyme and retained 100 % of its activity after incubation at 60 °C for 48 h. Our results clearly show that the truncated ThMan5A enzyme exhibited improved characteristics both in expression efficiency and in its thermal stability. These characteristics suggest that ThMan5AΔCBM has potential applications in the food, feed, paper, and pulp industries.

Homologous constitutive expression of Xyn III in Trichoderma reesei QM9414 and its characterization.

Xylanase III (Xyn III), a specific endoxylanase that belongs to family 10 of the glycoside hydrolases, was overexpressed in Trichoderma reesei QM9414 using a constitutive strong promoter of the gene encoding pyruvate decarboxylase (pdc). The maximum recombinant xylanase activity achieved was 817.2 ± 65.2 U/mL in the transformant fermentation liquid. The productivities of Xyn III accounted for approximately 53% of the total protein secreted by the recombinant. The enzyme was optimally active at 60 °C and pH 6. The recombinant Xyn III was stable at pH 5-8. This is the first report on the homologous expression of xyn3 in T. reesei QM9414. The properties of Xyn III make it promising in a variety of industrial use.