It is well known that abscisic acid (ABA)-induced leaf senescence and premature leaf senescence negatively affect the yield of rice (Oryza sativa). However, the molecular mechanism underlying this relationship, especially the upstream transcriptional network that modulates ABA level during leaf senescence, remains largely unknown. Here, we demonstrate a rice NAC transcription factor, OsNAC2, that participates in ABA-induced leaf senescence. Overexpression of OsNAC2 dramatically accelerated leaf senescence, whereas its knockdown lines showed a delay in leaf senescence. Chromatin immunoprecipitation-quantitative PCR, dual-luciferase, and yeast one-hybrid assays demonstrated that OsNAC2 directly activates expression of chlorophyll degradation genes, OsSGR and OsNYC3. Moreover, ectopic expression of OsNAC2 leads to an increase in ABA levels via directly up-regulating expression of ABA biosynthetic genes (OsNCED3 and OsZEP1) as well as down-regulating the ABA catabolic gene (OsABA8ox1). Interestingly, OsNAC2 is upregulated by a lower level of ABA but downregulated by a higher level of ABA, indicating a feedback repression of OsNAC2 by ABA. Additionally, reduced OsNAC2 expression leads to about 10% increase in the grain yield of RNAi lines. The novel ABA-NAC-SAGs regulatory module might provide a new insight into the molecular action of ABA to enhance leaf senescence and elucidates the transcriptional network of ABA production during leaf senescence in rice.Senescence is the last stage of leaf development. During this period, various changes occur at the physiological, biochemical, and molecular levels. For example, macromolecules including lipids, proteins, and nucleic acids are hydrolyzed, which leads to disassembly of mitochondria and nuclei, and to cell death (Buchanan-Wollaston et al., 2005;Ulker et al., 2007). Although senescence is an active process to salvage nutrients from old tissues, precocious senescence will shorten the growth stage of crops and be unfavorable to agronomic production (Woo et al., 2013).The most distinguishing feature in leaf senescence is the yellowing phenotype, which is a visible marker of the degradation of macromolecules (Kim et al., 2006). The chlorophyll degradation pathway is one of the most characterized ones for macromolecule degradation in plants (Hörtensteiner, 2006). Overexpressing NON-YELLOW COLORING1 (NYC1) or NYC1-like genes in rice (Oryza sativa) can induce degradation of chlorophyll . A pph (encoding pheophytinase) mutant is abnormal in chlorophyll degradation during senescence and therefore exhibits a stay-green phenotype (Schelbert et al., 2009). Mutation of the PAO (Pheophorbide a oxygenase) gene leads to retention of chlorophyll in leaves during dark-induced senescence in Arabidopsis (Arabidopsis thaliana; Pruzinská et al., 2005). Recently, the highly conserved STAY-GREEN (SGR) in higher plants has been identified to be chloroplast-localized dechelatase (Shimoda et al., 2016).The senescence process is highly regulated by a range of important factors. It has been demon...
These authors contributed equally to the work. SUMMARYPlant height and flowering time are key agronomic traits affecting yield in rice (Oryza sativa). In this study, we investigated the functions in rice growth and development of OsNAC2, encoding a NAC transcription factor in rice. Transgenic plants that constitutively expressed OsNAC2 had shorter internodes, shorter spikelets, and were more insensitive to gibberellic acid (GA 3 ). In addition, the levels of GAs decreased in OsNAC2 overexpression plants, compared with the wild-type. Moreover, flowering was delayed for approximately 5 days in transgenic lines. The transcription of Hd3a, a flowering-time related gene, was suppressed in transgenic lines. In addition, transgenic Arabidopsis plants expressing OsNAC2 were also more insensitive to GA 3 . The expression levels of GA biosynthetic genes OsKO2 and OsKAO were repressed. The expression of OsSLRL, encoding a repressor in the GA signal pathway, and OsEATB, which encodes a repressor of GA biosynthesis, were both enhanced. Western blotting indicated that DELLA also accumulated at the protein level. Dual-luciferase reporter analyses, yeast one-hybrid assays and ChIP-qPCR suggested that OsNAC2 directly interacted with the promoter of OsEATB and OsKO2. Taken together, we proposed that OsNAC2 is a negative regulator of the plant height and flowering time, which acts by directly regulating key genes of the GA pathway in rice.
Plants can perceive environmental changes and respond to external stressors. Here, we show that OsNAC2, a member of the NAC transcription factor family, was strongly induced by ABA and osmotic stressors such as drought and high salt. With reduced yields under drought conditions at the flowering stage, OsNAC2 overexpression lines had lower resistance to high salt and drought conditions. RNAi plants showed enhanced tolerance to high salinity and drought stress at both the vegetative and flowering stages. Furthermore, RNAi plants had improved yields after drought stress. A microarray assay indicated that many ABA-dependent stress-related genes were down-regulated in OsNAC2 overexpression lines. We further confirmed that OsNAC2 directly binds the promoters of LATE EMBRYOGENESIS ABUNDANT 3 (OsLEA3) and Stress-Activated Protein Kinases 1 (OsSAPK1), two marker genes in the abiotic stress and ABA response pathways, respectively. Our results suggest that in rice OsNAC2 regulates both abiotic stress responses and ABA-mediated responses, and acts at the junction between the ABA and abiotic stress pathways.
Single element switch Phase-change materials are attractive for computer memory and switching, in part due to their small size and fast switching speeds. However, competitive materials frequently have many elements, which decreases the switching reliability. Shen et al . built a pure tellurium device that is capable of fast switching through a phase transformation (see the Perspective by Calarco and Arciprete). Unlike many other phase-change materials, the change in resistance happens because the tellurium melts during the switching process. The resulting device can be switched 100 million times before failure and is an appealing route for avoiding the issues from multi-element phase-change materials. —BG
Doping is indispensable to tailor phase-change materials (PCM) in optical and electronic data storage. Very few experimental studies, however, have provided quantitative information on the distribution of dopants on the atomic-scale. Here, we present atom-resolved images of Ag and In dopants in Sb 2 Te-based (AIST) PCM using electron microscopy and atom-probe tomography. Combing these with DFT calculations and chemical-bonding analysis, we unambiguously determine the dopants’ role upon recrystallization. Composition profiles corroborate the substitution of Sb by In and Ag, and the segregation of excessive Ag into grain boundaries. While In is bonded covalently to neighboring Te, Ag binds ionically. Moreover, In doping accelerates the crystallization and hence operation while Ag doping limits the random diffusion of In atoms and enhances the thermal stability of the amorphous phase.
Phase change memory is widely considered as the most promising candidate as storage class memory (SCM), bridging the performance gaps between dynamic random access memory and flash. However, high required operation current remains the major limitation for the SCM application, even after using defect engineering materials, for example, Ti-doped Sb 2 Te 3 . Here, we demonstrate that ∼87% current can be reduced by spatially separating Sb 2 Te 3 and TiTe 2 layers, thanks to semimetallic TiTe 2 serving as a thermal barrier in the reset process. Moreover, the stable crystalline TiTe 2 layer provides an ordered interface to speed up the crystallization process of the amorphous Sb 2 Te 3 layer, enabling ∼10 ns ultrafast crystallization speed. An outstanding device lifetime, up to ∼2 × 10 7 cycles, has been obtained, which is twice as long as that of alloy-based cells. Correlative electron microscopy and atom probe tomography provide evidence that the TiTe 2 /Sb 2 Te 3 multilayer can keep a layer-stacked structure, avoiding phase segregation found in alloys and strong element intermixing in the GeTe/Sb 2 Te 3 superlattice, which enables excellent cyclability. This study suggests that adding a semimetallic layer in the phase change layer, such as TiTe 2 and TiSe 2 , can yield a phase change memory with superior properties. KEYWORDS: thermal barrier phase change material, atom probe tomography, Ti−Sb−Te, TiTe 2 , TiTe 2 /Sb 2 Te 3 , high endurance, low energy consumption
The search for ultrafast photonic memory devices is inspired by the ever‐increasing number of cloud‐computing, supercomputing, and artificial‐intelligence applications, together with the unique advantages of signal processing in the optical domain such as high speed, large bandwidth, and low energy consumption. By embracing silicon photonics with chalcogenide phase‐change materials (PCMs), non‐volatile integrated photonic memory is developed with promising potential in photonic integrated circuits and nanophotonic applications. While conventional PCMs suffer from slow crystallization speed, scandium‐doped antimony telluride (SST) has been recently developed for ultrafast phase‐change random‐access memory applications. An ultrafast non‐volatile photonic memory based on an SST thin film with a 2 ns write/erase speed is demonstrated, which is the fastest write/erase speed ever reported in integrated phase‐change photonic devices. SST‐based photonic memories exhibit multilevel capabilities and good stability at room temperature. By mapping the memory level to the biological synapse weight, an artificial neural network based on photonic memory devices is successfully established for image classification. Additionally, a reflective nanodisplay application using SST with optoelectronic modulation capabilities is demonstrated. Both the optical and electrical changes in SST during the phase transition and the fast‐switching speed demonstrate their potential for use in photonic computing, neuromorphic computing, nanophotonics, and optoelectronic applications.
The late embryogenesis abundant (LEA) protein family is a large protein family that is closely associated with resistance to abiotic stresses in many organisms, such as plants, bacteria and animals. In this study, we isolated a LEA gene, RcLEA, which was cytoplasm-localized, from Rosa chinensis. RcLEA was found to be induced by high temperature through RT-PCR. Overexpression of RcLEA in Escherichia coli improved its growth performance compared with the control under high temperature, low temperature, NaCl and oxidative stress conditions. RcLEA was also overexpressed in Arabidopsis thaliana. The transgenic Arabidopsis showed better growth after high and low temperature treatment and exhibited less peroxide according to 3, 3-diaminobenzidine staining. However, RcLEA did not improve the tolerance to NaCl or osmotic stress in Arabidopsis. In vitro analysis showed that RcLEA was able to prevent the freeze-thaw-induced inactivation or heat-induced aggregation of various substrates, such as lactate dehydrogenase and citrate synthase. It also protected the proteome of E. coli from denaturation when the proteins were heat-shocked or subjected to acidic conditions. Furthermore, bimolecular fluorescence complementation assays suggested that RcLEA proteins function in a complex manner by making the form of homodimers.
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