Low-Temperature-Mediated Promoter Methylation Relates to the Expression of TaPOR2D, Affecting the Level of Chlorophyll Accumulation in Albino Wheat (Triticum aestivum L.).

Chlorophyll is an indispensable photoreceptor in plant photosynthesis. Its anabolic imbalance is detrimental to individual growth and development. As an essential epigenetic modification, DNA methylation can induce phenotypic variations, such as leaf color transformation, by regulating gene expression. Albino line XN1376B is a natural mutation of winter wheat cultivar XN1376; however, the regulatory mechanism of its albinism is still unclear. In this study, we found that low temperatures induced albinism in XN1376B. The number of chloroplasts decreased as the phenomenon of bleaching intensified and the fence tissue and sponge tissue slowly dissolved. We identified six distinct TaPOR (protochlorophyllide oxidoreductase) genes in the wheat genome, and TaPOR2D was deemed to be related to the phenomenon of albinism based on the expression in different color leaves (green leaves, white leaves and returned green leaves) and the analysis of promoters' cis-acting elements. TaPOR2D was localized to chloroplasts. TaPOR2D overexpression (TaPOR2D-OE) enhanced the chlorophyll significantly in Arabidopsis, especially at two weeks; the amount of chlorophyll was 6.46 mg/L higher than in WT. The methylation rate of the TaPOR2D promoter in low-temperature albino leaves is as high as 93%, whereas there was no methylation in green leaves. Correspondingly, three DNA methyltransferase genes (TaMET1, TaDRM and TaCMT) were up-regulated in white leaves. Our study clarified that the expression of TaPOR2D is associated with its promoter methylation at a low temperature; it affects the level of chlorophyll accumulation, which probably causes the abnormal development of plant chloroplasts in albino wheat XN1376B. The results provide a theoretical basis for in-depth analysis of the regulation of development of plant chloroplasts and color variation in wheat XN1376B leaves.

Harnessing buckling to design tunable locally resonant acoustic metamaterials.

We report a new class of tunable and switchable acoustic metamaterials comprising resonating units dispersed into an elastic matrix. Each resonator consists of a metallic core connected to the elastomeric matrix through elastic beams, whose buckling is intentionally exploited as a novel and effective approach to control the propagation of elastic waves. We first use numerical analysis to show the evolution of the locally resonant band gap, fully accounting for the effect of nonlinear pre-deformation. Then, we experimentally measure the transmission of vibrations as a function of the applied loading in a finite-size sample and find excellent agreement with our numerical predictions. The proposed concept expands the ability of existing acoustic metamaterials by enabling tunability over a wide range of frequencies. Furthermore, we demonstrate that in our system the deformation can be exploited to turn on or off the band gap, opening avenues for the design of adaptive switches.

Complex ordered patterns in mechanical instability induced geometrically frustrated triangular cellular structures.

Geometrical frustration arises when a local order cannot propagate throughout the space because of geometrical constraints. This phenomenon plays a major role in many systems leading to disordered ground-state configurations. Here, we report a theoretical and experimental study on the behavior of buckling-induced geometrically frustrated triangular cellular structures. To our surprise, we find that buckling induces complex ordered patterns which can be tuned by controlling the porosity of the structures. Our analysis reveals that the connected geometry of the cellular structure plays a crucial role in the generation of ordered states in this frustrated system.

Active oxygen generation induced by the glucose sensor TaHXK7-1A decreased the drought resistance of transgenic Arabidopsis and wheat (Triticum aestivum L.).

Improving wheat drought resistance is of great significance for grain production and food security. Hexokinases (HXKs) play a role in sugar signal transduction and are involved in abiotic stress responses in wheat. To clarify the relationship between HXKs and drought stress in wheat, we used the rice active oxygen induction gene OsHXK1 as a reference sequence and the homologously cloned wheat TaHXK7-1A gene. TaHXK7-1A was localized in the nucleus and cell membrane. Under drought stress, over-expression of TaHXK7-1A increased the contents of O2·ï¼ and malondialdehyde (MDA) and significantly up-regulated the respiratory burst oxidative homologue (RBOHs) genes in transgenic Arabidopsis. In addition, the over-expression of TaHXK7-1A inhibited the growth of Arabidopsis seedlings and increased ROS accumulation under 6 % exogenous glucose treatment. Gene silencing of TaHXK7-1 decreased the contents of O2·ï¼ and MDA in wheat leaves under drought stress, and the RBOHs was significantly down-regulated, which improved the drought resistance of wheat. The results of yeast one-hybrid, EMSA, and dual-luciferase assays showed that TabHLH148-5A bound to the E-box motif of the TaHXK7-1A promoter and inhibited the expression of TaHXK7-1A. In addition, yeast two-hybrid and luciferase complementation imaging assays showed that TaHXK7-1A interacted with TaGRF3-4A. These results indicate that the glucose sensor TaHXK7-1A was negatively regulated by TabHLH148-5A, interacted with TaGRF3-4A, and negatively regulated wheat drought resistance by regulating RBOHs expression and inducing ROS production, thus providing a theoretical basis for revealing the molecular mechanism of wheat drought resistance.

Genome-Wide Identification and Expression Analysis of TUA and TUB Genes in Wheat (Triticum aestivum L.) during Its Development.

Microtubules play a fundamental role in plant development, morphogenesis, and cytokinesis; they are assembled from heterodimers containing an α-tubulin (TUA) and a ß-tubulin (TUB) protein. However, little research has been conducted on the TUA and TUB gene families in hexaploid wheat (Triticum aestivum L.). In this study, we identified 15 TaTUA and 28 TaTUB genes in wheat. Phylogenetic analysis showed that 15 TaTUA genes were divided into two major subfamilies, and 28 TaTUB genes were divided into five major subfamilies. Mostly, there were similar motif compositions and exon-intron structures among the same subfamilies. Segmental duplication of genes (WGD/segmental) is the main process of TaTUA and TaTUB gene family expansion in wheat. It was found that TaTUA and TaTUB genes presented specific temporal and spatial characteristics based on the expression profiles of 17 tissues during wheat development using publicly available RNA-seq data. It was worth noting, via qRT-PCR, that two TaTUA and five TaTUB genes were highly expressed in fertile anthers compared to male sterility. These were quite different between physiological male sterile lines and S-type cytoplasmic male sterile lines at different stages of pollen development. This study offers fundamental information on the TUA and TUB gene families during wheat development and provides new insights for exploring the molecular mechanism of wheat male sterility.

Harnessing Buckling to Design Architected Materials that Exhibit Effective Negative Swelling.

Inspired by the need to develop materials capable of targeted and extreme volume changes during operation, numerical simulations and experiments are combined to design a new class of soft architected materials that achieve a reduction of projected surface-area coverage during swelling.

Multistable Architected Materials for Trapping Elastic Strain Energy.

3D printing and numerical analysis are combined to design a new class of architected materials that contain bistable beam elements and exhibit controlled trapping of elastic energy. The proposed energy-absorbing structures are reusable. Moreover, the mechanism of energy absorption stems solely from the structural geometry of the printed beam elements, and is therefore both material- and loading-rate independent.

Buckling-induced reversible symmetry breaking and amplification of chirality using supported cellular structures.

Buckling-induced reversible symmetry breaking and amplification of chirality using macro- and microscale supported cellular structures is described. Guided by extensive theoretical analysis, cellular structures are rationally designed, in which buckling induces a reversible switching between achiral and chiral configurations. Additionally, it is demonstrated that the proposed mechanism can be generalized over a wide range of length scales, geometries, materials, and stimuli.

Multi-patterned dynamics of mitochondrial fission and fusion in a living cell.

Mitochondria are highly-dynamic organelles, but it is challenging to monitor quantitatively their dynamics in a living cell. Here we developed a novel approach to determine the global occurrence of mitochondrial fission and fusion events in living human epithelial cells (Hela) and mouse embryonic fibroblast cells (MEF). Distinct patterns of sequential events including fusion followed by fission (Fu-Fi), the so-called "kiss and run" model previously described, fission followed by fusion (Fi-Fu), fusion followed by fusion (Fu-Fu), and fission followed by fission (Fi-Fi) were observed concurrently. The paired events appeared in high frequencies with short lifetimes and large sizes of individual mitochondria, as compared to those for unpaired events. The high frequencies of paired events were found to be biologically significant. The presence of membrane uncoupler CCCP enhanced the frequency of paired events (from both Fu-Fi and Fi-Fu patterns) with a reduced mitochondrial size. Knock-out of mitofusin protein Mfn1 increased the frequency of fission with increased lifetime of unpaired events whereas deletion of both Mfn1 and Mfn2 resulted in an instable dynamics. These results indicated that the paired events were dominant but unpaired events were not negligible, which provided a new insight into mitochondrial dynamics. In addition to kiss and run model of action, our data suggest that, from a global visualization over an entire cell, multiple patterns of action appeared in mitochondrial fusion and fission.