Salinity-Triggered Responses in Plant Apical Meristems for Developmental Plasticity.

Salt stress severely affects plant growth and development. The plant growth and development of a sessile organism are continuously regulated and reformed in response to surrounding environmental stress stimuli, including salinity. In plants, postembryonic development is derived mainly from primary apical meristems of shoots and roots. Therefore, to understand plant tolerance and adaptation under salt stress conditions, it is essential to determine the stress response mechanisms related to growth and development based on the primary apical meristems. This paper reports that the biological roles of microRNAs, redox status, reactive oxygen species (ROS), nitric oxide (NO), and phytohormones, such as auxin and cytokinin, are important for salt tolerance, and are associated with growth and development in apical meristems. Moreover, the mutual relationship between the salt stress response and signaling associated with stem cell homeostasis in meristems is also considered.

Heterotrimeric G Protein-Mediated Signaling Is Involved in Stress-Mediated Growth Inhibition in Arabidopsis thaliana.

Heterotrimeric G protein-mediated signaling plays a vital role in physiological and developmental processes in eukaryotes. On the other hand, because of the absence of a G protein-coupled receptor and self-activating mechanism of the Gα subunit, plants appear to have different regulatory mechanisms, which remain to be elucidated, compared to canonical G protein signaling established in animals. Here we report that Arabidopsis heterotrimeric G protein subunits, such as Gα (GPA1) and Gß (AGB1), regulate plant growth under stress conditions through the analysis of heterotrimeric G protein mutants. Flg22-mediated growth inhibition in wild-type roots was found to be caused by a defect in the elongation zone, which was partially blocked in agb1-2 but not gpa1-4. These results suggest that AGB1 may negatively regulate plant growth under biotic stress conditions. In addition, GPA1 and AGB1 exhibited genetically opposite effects on FCA-mediated growth inhibition under heat stress conditions. Therefore, these results suggest that plant G protein signaling is probably related to stress-mediated growth regulation for developmental plasticity in response to biotic and abiotic stress conditions.

A review on intense pulsed light process as post-treatment for metal oxide thin films and nanostructures for device application.

The intense pulsed light (IPL) post-treatment process has attracted great attention in the device fabrication due to its versatility and rapidity particularly for solution process functional structures in devices, flexible/printed electronics, and continuous manufacturing process. The metal oxide materials inherently have multi-functionality and have been widely used in form of thin films or nanostructures in device application such as thin film transistors, light emitting diodes, solar cells, supercapacitors, etc. The IPL treatment enhances the physical and/or chemical properties of the functional metal oxide through photothermal effects. However, most metal oxides are transparent to most range of visible light and require more energy for post-treatment. In this review, we have summarized the IPL post-treatment processes for metal oxide thin films and nanostructures in device applications. The sintering and annealing of metal oxides using IPL improved the device performances by employing additional light absorbing layer or back-reflector. The IPL process becomes an innovative versatile post-treatment process in conjunction with multi-functional metal oxides in near-future device applications.

CCOAOMT1, a candidate cargo secreted via VAMP721/722 secretory vesicles in Arabidopsis.

We previously found that VAMP721/722 SNARE proteins guide secretory vesicles to pathogen-attacking sites during immune responses in Arabidopsis, which suggests that these vesicles should deliver immune molecules. However, the lethality of vamp721 vamp722 double null mutant makes it difficult to understand the nature of cargo transported via VAMP721/722 vesicles. Since VAMP721/722-depleted (VAMP721+/-VAMP722-/- and VAMP721-/-VAMP722+/-) plants show compromised resistance to extracellular pathogens, we assume that an immune protein secreted through the VAMP721/722-engaged exocytosis would be remained more in VAMP721/722-depleted plants than WT. By comparing intracellular proteins between WT and VAMP721/722-depleted plants, we found caffeoyl-CoA O-methyltransferase 1 (CCOAOMT1) involved in the lignin biosynthesis was more abundantly detected in both VAMP721/722-depleted lines than WT. Plants are well-known to deposit secondary cell walls as physical barriers at pathogen-attempting sites. Therefore, extracellular detection of CCOAOMT1 and impaired resistance to Pseudomonas syringae DC3000 in ccoaomt1 plants suggest that plants secrete cell wall-modifying enzymes at least including CCOAOMT1 to reinforce the secondary cell walls for immunity.

Type II Ice-Binding Proteins Isolated from an Arctic Microalga Are Similar to Adhesin-Like Proteins and Increase Freezing Tolerance in Transgenic Plants.

Microalgal ice-binding proteins (IBPs) in the polar region are poorly understood at the genome-wide level, although they are important for cold adaptation. Through the transcriptome study with the Arctic green alga Chloromonas sp. KNF0032, we identified six Chloromonas IBP genes (CmIBPs), homologous with the previously reported IBPs from Antarctic snow alga CCMP681 and Antarctic Chloromonas sp. They were organized with multiple exon/intron structures and low-temperature-responsive cis-elements in their promoters and abundantly expressed at low temperature. The biological functions of three representative CmIBPs (CmIBP1, CmIBP2 and CmIBP3) were tested using in vitro analysis and transgenic plant system. CmIBP1 had the most effective ice recrystallization inhibition (IRI) activities in both in vitro and transgenic plants, and CmIBP2 and CmIBP3 had followed. All transgenic plants grown under nonacclimated condition were freezing tolerant, and especially 35S::CmIBP1 plants were most effective. After cold acclimation, only 35S::CmIBP2 plants showed slightly increased freezing tolerance. Structurally, the CmIBPs were predicted to have ß-solenoid forms with parallel ß-sheets and repeated TXT motifs. The repeated TXT structure of CmIBPs appears similar to the AidA domain-containing adhesin-like proteins from methanogens. We have shown that the AidA domain has IRI activity as CmIBPs and phylogenetic analysis also supported that the AidA domains are monophyletic with ice-binding domain of CmIBPs, and these results suggest that CmIBPs are a type of modified adhesins.

Brassinosteroids facilitate xylem differentiation and wood formation in tomato.

MAIN CONCLUSION: BR signaling pathways facilitate xylem differentiation and wood formation by fine tuning SlBZR1/SlBZR2-mediated gene expression networks involved in plant secondary growth. Brassinosteroid (BR) signaling and BR crosstalk with diverse signaling cues are involved in the pleiotropic regulation of plant growth and development. Recent studies reported the critical roles of BR biosynthesis and signaling in vascular bundle development and plant secondary growth; however, the molecular bases of these roles are unclear. Here, we performed comparative physiological and anatomical analyses of shoot morphological growth in a cultivated wild-type tomato (Solanum lycopersicum cv. BGA) and a BR biosynthetic mutant [Micro Tom (MT)]. We observed that the canonical BR signaling pathway was essential for xylem differentiation and sequential wood formation by facilitating plant secondary growth. The gradual retardation of xylem development phenotypes during shoot vegetative growth in the BR-deficient MT tomato mutant recovered completely in response to exogenous BR treatment or genetic complementation of the BR biosynthetic DWARF (D) gene. By contrast, overexpression of the tomato Glycogen synthase kinase 3 (SlGSK3) or CRISPR-Cas9 (CR)-mediated knockout of the tomato Brassinosteroid-insensitive 1 (SlBRI1) impaired BR signaling and resulted in severely defective xylem differentiation and secondary growth. Genetic modulation of the transcriptional activity of the tomato Brassinazole-resistant 1/2 (SlBZR1/SlBZR2) confirmed the positive roles of BR signaling pathways for xylem differentiation and secondary growth. Our data indicate that BR signaling pathways directly promote xylem differentiation and wood formation by canonical BR-activated SlBZR1/SlBZR2.

Mitogen-activated protein kinases MPK3 and MPK6 are required for stem cell maintenance in the Arabidopsis shoot apical meristem.

KEY MESSAGE: CLV3p-mediated phosphorylation of MPK3 and MPK6 occurs via CLV1 and BAM1 receptors to regulate the maintenance of SAM development. The CLAVATA peptide-receptor (CLV3p-CLV1) pathway modulates a homeodomain master regulator WUSCHEL (WUS) transcription factor in the shoot apical meristem (SAM) with poorly defined signaling mechanisms. Here, we report that mitogen-activated protein kinases (MAPKs, also known as MPKs in plants) act in an intracellular signaling cascade to play an important role in the maintenance of SAM development. Interestingly, the application of exogenous CLV3p triggers rapid signaling in the SAM via dynamic activation of MPK3 and MPK6, which are positively regulated by both CLV1 and BARELY ANY MERISTEM 1 (BAM1) receptors. Surprisingly, the timing of MAPK activation is tightly correlated with the transcriptional repression of WUS expression in the SAM, indicating a fast CLV3p-CLV1/BAM1 signaling event. Furthermore, conditional mpk3,6 double mutants exhibited CLV3p insensitivity in stem cell maintenance manifested by the persistent SAM growth in the presence of exogenous CLV3p signals, as well as elevated WUS expression and repressed WUS-specific target genes. Taken together, these results suggest that MPK3 and MPK6 activated by CLV3p signals through mainly CLV1 and BAM1 receptors are key regulators controlling stem cell homeostasis in the SAM.

Stem-cell-triggered immunity through CLV3p-FLS2 signalling.

Stem cells in the shoot apical meristem (SAM) of plants are the self-renewable reservoir for leaf, stem and flower organogenesis. In nature, disease-free plants can be regenerated from SAM despite infections elsewhere, which underlies a horticultural practice for decades. However, the molecular basis of the SAM immunity remains unclear. Here we show that the CLAVATA3 peptide (CLV3p), expressed and secreted from stem cells and functioning as a key regulator of stem-cell homeostasis in the SAM of Arabidopsis, can trigger immune signalling and pathogen resistance via the flagellin receptor kinase FLS2 (refs 5, 6). CLV3p-FLS2 signalling acts independently from the stem-cell signalling pathway mediated through CLV1 and CLV2 receptors, and is uncoupled from FLS2-mediated growth suppression. Endogenous CLV3p perception in the SAM by a pattern recognition receptor for bacterial flagellin, FLS2, breaks the previously defined self and non-self discrimination in innate immunity. The dual perception of CLV3p illustrates co-evolution of plant peptide and receptor kinase signalling for both development and immunity. The enhanced immunity in SAM or germ lines may represent a common strategy towards immortal fate in plants and animals.

Dual CLAVATA3 Peptides in Arabidopsis Shoot Stem Cell Signaling.

Plant shoot stem cell pool is constantly maintained by a negative feedback loop through peptide-receptor mediated signaling pathway. CLAVATA3 (CLV3) encode a 96 amino-acid protein which is processed to 12-amino-acid or arabinosylated 13-amino-acid peptides, acting as a ligand signal to regulate stem cell homeostasis in the shoot apical meristem (SAM). Although arabinosylated 13-amino-acid CLV3 peptide (CLV3p) shows more significant binding affinity to its receptors and biological activities in the SAM, the physiological function of two mature forms of CLV3p remained an unresolved puzzle in the past decade due to the technical difficulties of arabinosylation modification in the peptide synthesis. Here, we analyzed the role of two mature CLV3 peptides with newly synthesized arabinosylated peptide. Beside shoot meristem phenotypes, arabinosylated CLV3p showed the conventional trait of CLV2-dependent root growth inhibition. Moreover, both 12-amino-acid and arabinosylated 13-amino-acid CLV3 peptides have analogous activities in shoot stem cell signaling. Notably, we demonstrated that non-arabinosylated 12-amino acid CLV3p can affect shoot stem cell signaling at the physiological level unlike previously suggested (Ohyama et al., 2009; Shinohara and Matsubayashi, 2013; Shinohara and Matsubayashi, 2015). Therefore, these results support the physiological role of the 12-amino-acid CLV3p in shoot stem cell signaling in the deficient condition of arabinosylated 13-amino-acid CLV3p in Arabidopsis thaliana.

Differential innate immune signalling via Ca(2+) sensor protein kinases.

Innate immunity represents the first line of inducible defence against microbial infection in plants and animals. In both kingdoms, recognition of pathogen- or microbe-associated molecular patterns (PAMPs or MAMPs, respectively), such as flagellin, initiates convergent signalling pathways involving mitogen-activated protein kinase (MAPK) cascades and global transcriptional changes to boost immunity. Although Ca(2+) has long been recognized as an essential and conserved primary mediator in plant defence responses, how Ca(2+) signals are sensed and relayed into early MAMP signalling is unknown. Using a functional genomic screen and genome-wide gene expression profiling, here we show that four calcium-dependent protein kinases (CDPKs) are Ca(2+)-sensor protein kinases critical for transcriptional reprogramming in plant innate immune signalling. Unexpectedly, CDPKs and MAPK cascades act differentially in four MAMP-mediated regulatory programs to control early genes involved in the synthesis of defence peptides and metabolites, cell wall modifications and redox signalling. Transcriptome profile comparison suggests that CDPKs are the convergence point of signalling triggered by most MAMPs. Double, triple and quadruple cpk mutant plants display progressively diminished oxidative burst and gene activation induced by the 22-amino-acid peptide flg22, as well as compromised pathogen defence. In contrast to negative roles of calmodulin and a calmodulin-activated transcription factor in plant defence, the present study reveals Ca(2+) signalling complexity and demonstrates key positive roles of specific CDPKs in initial MAMP signalling.

Roll-to-Roll Gravure Coating of PVDF on a Battery Separator for the Enhancement of Thermal Stability.

The polyethylene lithium-ion battery separator is coated with a polymer by means of a roll-to-roll (R2R) gravure coating scheme to enhance the thermal stability. The polyvinylidene fluoride (PVDF) or polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) is gravure-coated, and the pores are fabricated based on online nonsolvent-induced phase separation (NIPS). N-methylpyrrolidone is used as a solvent, and deionized water or a methanol mixture thereof is exploited as a nonsolvent in NIPS. Scanning electron microscopy confirms that the polymer film is formed and that the pores are well developed. The thermal shrinkage decreased by 20.0% and 23.2% compared to that of the bare separator due to the coating of PVDF and PVDF-HFP, respectively. The R2R gravure coating scheme is proven to be fully functional to tailor the properties of lithium-ion battery separators.

Absorption-Dominant mmWave EMI Shielding Films with Ultralow Reflection using Ferromagnetic Resonance Frequency Tunable M-Type Ferrites.

Although there is a high demand for absorption-dominant electromagnetic interference (EMI) shielding materials for 5G millimeter-wave (mmWave) frequencies, most current shielding materials are based on reflection-dominant conductive materials. While there are few absorption-dominant shielding materials proposed with magnetic materials, their working frequencies are usually limited to under 30 GHz. In this study, a novel multi-band absorption-dominant EMI shielding film with M-type strontium ferrites and a conductive grid is proposed. This film shows ultralow EMI reflection of less than 5% in multiple mmWave frequency bands with sub-millimeter thicknesses, while shielding more than 99.9% of EMI. The ultralow reflection frequency bands are controllable by tuning the ferromagnetic resonance frequency of M-type strontium ferrites and composite layer geometries. Two examples of shielding films with ultralow reflection frequencies, one for 39 and 52 GHz 5G telecommunication bands and the other for 60 and 77 GHz autonomous radar bands, are presented. The remarkably low reflectance and thinness of the proposed films provide an important advancement toward the commercialization of EMI shielding materials for 5G mmWave applications.

Regulation of Flowering Time and Other Developmental Plasticities by 3' Splicing Factor-Mediated Alternative Splicing in Arabidopsis thaliana.

Plants, as sessile organisms, show a high degree of plasticity in their growth and development and have various strategies to cope with these alterations under continuously changing environments and unfavorable stress conditions. In particular, the floral transition from the vegetative and reproductive phases in the shoot apical meristem (SAM) is one of the most important developmental changes in plants. In addition, meristem regions, such as the SAM and root apical meristem (RAM), which continually generate new lateral organs throughout the plant life cycle, are important sites for developmental plasticity. Recent findings have shown that the prevailing type of alternative splicing (AS) in plants is intron retention (IR) unlike in animals; thus, AS is an important regulatory mechanism conferring plasticity for plant growth and development under various environmental conditions. Although eukaryotes exhibit some similarities in the composition and dynamics of their splicing machinery, plants have differences in the 3' splicing characteristics governing AS. Here, we summarize recent findings on the roles of 3' splicing factors and their interacting partners in regulating the flowering time and other developmental plasticities in Arabidopsis thaliana.

Crosstalk between cold response and flowering in Arabidopsis is mediated through the flowering-time gene SOC1 and its upstream negative regulator FLC.

The appropriate timing of flowering is pivotal for reproductive success in plants; thus, it is not surprising that flowering is regulated by complex genetic networks that are fine-tuned by endogenous signals and environmental cues. The Arabidopsis thaliana flowering-time gene SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1) encodes a MADS box transcription factor and is one of the key floral activators integrating multiple floral inductive pathways, namely, long-day, vernalization, autonomous, and gibberellin-dependent pathways. To elucidate the downstream targets of SOC1, microarray analyses were performed. The analysis revealed that the soc1-2 knockout mutant has increased, and an SOC1 overexpression line has decreased, expression of cold response genes such as CBFs (for CRT/DRE binding factors) and COR (for cold regulated) genes, suggesting that SOC1 negatively regulates the expression of the cold response genes. By contrast, overexpression of cold-inducible CBFs caused late flowering through increased expression of FLOWERING LOCUS C (FLC), an upstream negative regulator of SOC1. Our results demonstrate the presence of a feedback loop between cold response and flowering-time regulation; this loop delays flowering through the increase of FLC when a cold spell is transient as in fall or early spring but suppresses the cold response when floral induction occurs through the repression of cold-inducible genes by SOC1.

Transcriptomics Using the Enriched Arabidopsis Shoot Apex Reveals Developmental Priming Genes Involved in Plastic Plant Growth under Salt Stress Conditions.

In the shoot apical meristem (SAM), the homeostasis of the stem cell population supplying new cells for organ formation is likely a key mechanism of multicellular plant growth and development. As plants are sessile organisms and constantly encounter environmental abiotic stresses, postembryonic development from the shoot stem cell population must be considered with surrounding abiotic stresses for plant adaptation. However, the underlying molecular mechanisms for plant adaptation remain unclear. Previous studies found that the stem-cell-related mutant clv3-2 has the property of salt tolerance without the differential response of typical stress-responsive genes compared to those in WT Ler. Based on these facts, we hypothesized that shoot meristems contain developmental priming genes having comprehensively converged functions involved in abiotic stress response and development. To better understand the biological process of developmental priming genes in the SAM, we performed RNA sequencing (RNA-seq) and transcriptome analysis through comparing genome-wide gene expression profiles between enriched shoot apex and leaf tissues. As a result, 121 putative developmental priming genes differentially expressed in the shoot apex compared to the leaf were identified under normal and salt stress conditions. RNA-seq experiments also revealed the shoot apex-specific responsive genes for salt stress conditions. Based on combinatorial comparisons, 19 developmental priming genes were finally identified, including developmental genes related to cell division and abiotic/biotic-stress-responsive genes. Moreover, some priming genes showed CLV3-dependent responses under salt stress conditions in the clv3-2. These results presumably provide insight into how shoot meristem tissues have relatively high viability against stressful environmental conditions for the developmental plasticity of plants.

Pure Piezoelectricity Generation by a Flexible Nanogenerator Based on Lead Zirconate Titanate Nanofibers.

Lead zirconate titanate (PbZr0.52Ti0.48O3, PZT) alloys have been extensively studied to be used for piezoelectric nanogenerators to harvest energy from mechanical motions. In this study, PZT nanofiber-based nanogenerators were fabricated to test their true piezoelectric performance without the triboelectric effect. Aligned PZT nanofibers were fabricated by a sol-gel electrospinning process. The thickness, area, and orientation of the PZT textile made by electrospinning a PZT solution onto multipair metal wires or metal mesh were controlled to form a composite textile. After the calcination, the PZT textile mixed with polydimethylsiloxane was placed between two flexible indium-doped tin oxide-polyethylene naphthalate substrates. The performance parameters of the nanogenerators were investigated under the bending motion, which excludes the triboelectric effect. An assembled nanogenerator of an area of 8 cm2 and a thickness of 80 µm could generate an electrical output voltage of 1.1 V and a current of 1.4 µA under the bending strain. The piezoelectric voltage depended on the thickness of the PZT textile, whereas the piezoelectric current depended on both the thickness and the area of the PZT textile. The electrical performance of the device was significantly affected by the orientation of the PZT fiber and the bending direction. The output voltage and the output current were strain-dependent, whereas the total integrated charge was independent of the strain rate. The properties of the flexible nanogenerator could be quantified to verify the pure piezoelectric performance of the device.

ABSCISIC ACID-INSENSITIVE 3 is involved in brassinosteroid-mediated regulation of flowering in plants.

ABSCISIC ACID-INSENSITIVE 3 (ABI3) is one of the essential transcription factors of ABSCISIC ACID (ABA) signaling, functioning in seed germination, early seedling development, and abiotic stress tolerance. A recent study showed that epigenetic repression of ABI3 by brassinosteroid (BR)-activated BRI1 EMS SUPPRESSOR1 (BES1)-TOPLESS (TPL)HISTONE DEACETYLASE 19 (HDA19) repressor complex is a critical event for promoting seed germination and early seedling development. However, other physiological roles of the repression of ABI3 and ABA responses by BES1-mediated BR signaling pathways remain elusive. Here, we show that BES1-mediated suppression of ABI3 promotes floral transition and ABI3 acts as a negative regulator for flowering. Ectopic expression of ABI3 specifically compromised the early flowering phenotype of bes1-D and induced severe late-flowering phenotypes in wild-type Arabidopsis and Solanum lycopersicum plants. Both spatiotemporal expression patterns and global transcriptome analysis of ABI3-overexpressing plants supported the biological roles of ABI3 in the negative regulation of floral transition and reproduction. Finally, we confirmed that the loss of function of ABI3 induced early-flowering phenotypes in both long- and short-day conditions. In conclusion, our data suggest that BES1-mediated regulation of ABI3 is important in the reproductive phase transition of plants.

Comparative transcriptome analysis of field- and chamber-grown samples of Colobanthus quitensis (Kunth) Bartl, an Antarctic flowering plant.

Colobanthus quitensis is one of the two vascular plants inhabiting the Antarctic. In natural habitats, it grows in the form of a cushion or mats, commonly observed in high latitudes or alpine vegetation. Although this species has been investigated over many years to study its geographical distribution and physiological adaptations to climate change, very limited genetic information is available. The high-throughput sequencing with a de novo assembly analysis yielded 47,070 contigs with blast-hits. Through the functional classification and enrichment analysis, we identified that photosynthesis and phenylpropanoid pathway genes show differential expression depending on the habitat environment. We found that the known 'plant core environmental stress response (PCESR)' genes were abundantly expressed in Antarctic samples, and confirmed that their expression is mainly induced by low-temperature. In addition, we suggest that differential expression of thermomorphogenesis-related genes may contribute to phenotypic plasticity of the plant, for instance, displaying a cushion-like phenotype to adapt to harsh environments.

Phenotypic alteration of eukaryotic cells using randomized libraries of artificial transcription factors.

We have developed a method in which randomized libraries of zinc finger-containing artificial transcription factors are used to induce phenotypic variations in yeast and mammalian cells. By linking multiple zinc-finger domains together, we constructed more than 100,000 zinc-finger proteins with diverse DNA-binding specificities and fused each of them to either a transcription activation or repression domain. The resulting transcriptional regulatory proteins were expressed individually in cells, and the transfected cells were screened for various phenotypic changes, such as drug resistance, thermotolerance or osmotolerance in yeast, and differentiation in mammalian cells. Genes associated with the selected phenotypes were also identified. Our results show that randomized libraries of artificial transcription factors are useful tools for functional genomics and phenotypic engineering.