Cryo-EM structures of the plant plastid-encoded RNA polymerase.

Chloroplasts are green plastids in the cytoplasm of eukaryotic algae and plants responsible for photosynthesis. The plastid-encoded RNA polymerase (PEP) plays an essential role during chloroplast biogenesis from proplastids and functions as the predominant RNA polymerase in mature chloroplasts. The PEP-centered transcription apparatus comprises a bacterial-origin PEP core and more than a dozen eukaryotic-origin PEP-associated proteins (PAPs) encoded in the nucleus. Here, we determined the cryo-EM structures of Nicotiana tabacum (tobacco) PEP-PAP apoenzyme and PEP-PAP transcription elongation complexes at near-atomic resolutions. Our data show the PEP core adopts a typical fold as bacterial RNAP. Fifteen PAPs bind at the periphery of the PEP core, facilitate assembling the PEP-PAP supercomplex, protect the complex from oxidation damage, and likely couple gene transcription with RNA processing. Our results report the high-resolution architecture of the chloroplast transcription apparatus and provide the structural basis for the mechanistic and functional study of transcription regulation in chloroplasts.

Hierarchical regulatory module GENOMES UNCOUPLED1-GOLDEN2-LIKE1/2-WRKY18/40 modulates salicylic acid signaling.

Chloroplast-to-nucleus retrograde signaling (RS) pathways are critical in modulating plant development and stress adaptation. Among chloroplast proteins mediating RS pathways, GENOMES UNCOUPLED1 (GUN1) represses the transcription of the nuclear transcription factors GOLDEN2-LIKE1 (GLK1) and GLK2 that positively regulate chloroplast biogenesis. Given the extensive exploration of the function of GUN1 in biogenic RS carried out in previous years, our understanding of its role in plant stress responses remains scarce. Here, we revealed that GUN1 contributes to the expression of salicylic acid (SA)-responsive genes (SARGs) through transcriptional repression of GLK1/2 in Arabidopsis (Arabidopsis thaliana). Loss of GUN1 significantly compromised the SA responsiveness in plants, concomitant with the upregulation of GLK1/2 transcripts. In contrast, knockout of GLK1/2 potentiated the expression of SARGs and led to enhanced stress responses. Chromatin immunoprecipitation, coupled with quantitative PCR and related reverse genetic approaches, unveiled that in gun1, GLK1/2 might modulate SA-triggered stress responses by stimulating the expression of WRKY18 and WRKY40, transcriptional repressors of SARGs. In summary, we demonstrate that a hierarchical regulatory module, consisting of GUN1-GLK1/2-WRKY18/40, modulates SA signaling, opening a research avenue regarding a latent GUN1 function in plant-environment interactions.

Syngas Production via CO2 Reforming of Methane over Aluminum-Promoted NiO-10Al2O3-ZrO2 Catalyst.

CO2 reforming of methane was studied at medium temperature (700 °C) using a GSHV of 48,000 h-1 over nickel catalysts supported on ZrO2 promoted by alumina. The catalysts were prepared by a one-step synthesis method and characterized by BET, H2-TPR, XRD, XPS, TEM, Raman spectroscopy, and TGA. The NiO-10Al2O3-ZrO2 catalyst exhibited higher catalytic performance in comparison with the NiO-ZrO2 catalyst. The enhancement of catalytic activity in dry reforming could be associated with the alterations in surface properties due to Al promotion. First, the Al promoter could modify the structure of ZrO2, leading to an increase of its pore volume and pore diameter. Second, the NiO-10Al2O3-ZrO2 catalyst exhibited high resistance to sintering. Third, the NiO-10Al2O3-ZrO2 catalyst showed high suppression to the loss of nickel during a long-term catalytic test. Finally, the addition of Al could inhibit the reduction of ZrO2 during the reduction and reaction, endowing further the stability.

Simple and fast colorimetric and electrochemical methods for the ultrasensitive detection of glucose.

Developing ultrasensitive and user-friendly methods for the detection glucose has attracted more and more attention. By virtue of high selectivity and sensitivity, enzyme-based glucose sensor plays a key role in point-of-care sensing technology for detecting glucose concentration. In this study, Amplex Red (AR), as both indicator and mediator, was investigated to detect glucose in presence of glucose oxidase (GOx) enzymes using colorimetric and electrochemical methods. Without using any advanced techniques and sophisticated nanomaterials, 1 µM glucose can be easily detected through simply detecting the solution color with a visual colorimetric method. On the other hand, the electrochemical method can provide much higher sensitivity for the detection of glucose, which achieves a linear range spanning from 20 nM to 3.56 µM with a limit of 7.3 nM (signal-to-noise ratio SNR = 3). It is also found that the presence of other sugars such as fructose, lactose, and maltose have very limited interference effects on the detection of glucose. More importantly, a bare GC electrode was used in all these electrochemical measurements without any electrode surface modification, guaranteeing a simple and fast operation. The analytical platforms for the detection of glucose presented here not only provide simple, fast, and ultrasensitive methods, but also have the potential to advance the sensing technology in the application of other health diagnostic research areas. Amplex Red (AR) was reported as both an indicator and mediator for the sensitive and specific determination of glucose using the colorimetric and electrochemical methods. The detection limit was 1 µM glucose by the visual colorimetric methods. A bare glassy carbon electrode without any functional modification was employed for the detection as low as 20 nM glucose with LOD of 7.3 nm (SNR = 3) in the electrochemical method.

From Golden Rice to aSTARice: Bioengineering Astaxanthin Biosynthesis in Rice Endosperm.

Carotenoids are important phytonutrients with antioxidant properties, and are widely used in foods and feedstuffs as supplements. Astaxanthin, a red-colored ketocarotenoid, has strong antioxidant activity and thus can benefit human health. However, astaxanthin is not produced in most higher plants. Here we report the bioengineering of astaxanthin biosynthesis in rice endosperm by introducing four synthetic genes, sZmPSY1, sPaCrtI, sCrBKT, and sHpBHY, which encode the enzymes phytoene synthase, phytoene desaturase, ß-carotene ketolase, and ß-carotene hydroxylase, respectively. Transgneic overexpression of two (sZmPSY1 and sPaCrtI), three (sZmPSY1, sPaCrtI and sCrBKT), and all these four genes driven by rice endosperm-specific promoters established the carotenoid/ketocarotenoid/astaxanthin biosynthetic pathways in the endosperm and thus resulted in various types of germplasm, from the yellow-grained ß-carotene-enriched Golden Rice to orange-red-grained Canthaxanthin Rice and Astaxanthin Rice, respectively. Grains of Astaxanthin Rice were enriched with astaxanthin in the endosperm and had higher antioxidant activity. These results proved that introduction of a minimal set of four transgenes enables de novo biosynthesis of astaxanthin in the rice endosperm. This work provides a successful example for synthetic biology in plants and biofortification in crops; the biofortified rice products generated by this study could be consumed as health-promoting foods and processed to produce dietary supplements.