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Photosynthetic rate is determined by CO2 fixation and CO2 entry into the plant through pores in the leaf epidermis called stomata. However, the effect of increased stomatal density on photosynthetic rate remains unclear. This work investigated the effect of alteration of stomatal density on leaf photosynthetic capacity in Arabidopsis thaliana. Stomatal density was modulated by overexpressing or silencing STOMAGEN, a positive regulator of stomatal development. Leaf photosynthetic capacity and plant growth were examined in transgenic plants. Increased stomatal density in STOMAGEN-overexpressing plants enhanced the photosynthetic rate by 30% compared to wild-type plants. Transgenic plants showed increased stomatal conductance under ambient CO2 conditions and did not show alterations in the maximum rate of carboxylation, indicating that the enhancement of photosynthetic rate was caused by gas diffusion changes. A leaf photosynthesis-intercellular CO2 concentration response curve showed that photosynthetic rate was increased under high CO2 conditions in association with increased stomatal density. STOMAGEN overexpression did not alter whole plant biomass, whereas its silencing caused biomass reduction. Our results indicate that increased stomatal density enhanced leaf photosynthetic capacity by modulating gas diffusion. Stomatal density may be a target trait for plant engineering to improve photosynthetic capacity.

Vacuolar processing enzyme (VPE) is a cysteine-type endopeptidase that has a substrate-specificity for asparagine or aspartic acid residues and cleaves peptide bonds at their carboxylterminal side. Various vacuolar proteins are synthesized as larger proprotein precursors, and VPE is an important initiator of maturation and activation of these proteins. It mediates programmed cell death (PCD) by provoking vacuolar rupture and initiating the proteolytic cascade leading to PCD. Vacuolar processing enzyme also possesses a peptide ligation activity, which is responsible for producing cyclic peptides in several plant species. These unique functions of VPE support developmental and environmental responses in plants. The number of VPE homologues is higher in angiosperm species, indicating that there has been differentiation and specialization of VPE function over the course of evolution. Angiosperm VPEs are separated into two major types: the γ-type VPEs, which are expressed mainly in vegetative organs, and the β-type VPEs, whose expression occurs mainly in storage organs; in eudicots, the δ-type VPEs are further separated within γ-type VPEs. This review also considers the importance of processing and peptide ligation by VPE in vacuolar protein maturation.

Boron uptake in Arabidopsis thaliana is mediated by nodulin 26-like intrinsic protein 5;1 (NIP5;1), a boric acid channel that is located preferentially on the soil side of the plasma membrane in root cells. However, the mechanism underlying this polar localization is poorly understood. Here, we show that the polar localization of NIP5;1 in epidermal and endodermal root cells is mediated by the phosphorylation of Thr residues in the conserved TPG (ThrProGly) repeat in the N-terminal region of NIP5;1. Although substitutions of Ala for three Thr residues in the TPG repeat did not affect lateral diffusion in the plasma membrane, these substitutions inhibited endocytosis and strongly compromised the polar localization of GFP-NIP5;1. Consistent with this, the polar localization was compromised in m subunit mutants of the clathrin adaptor AP2. The Thr-to-Ala substitutions did not affect the boron transport activity of GFP-NIP5;1 in Xenopus laevis oocytes but did inhibit the ability to complement boron translocation to shoots and rescue growth defects in nip5;1-1 mutant plants under boron-limited conditions. These results demonstrate that the polar localization of NIP5;1 is maintained by clathrin-mediated endocytosis, is dependent on phosphorylation in the TPG repeat, and is necessary for the efficient transport of boron in roots.

The nuclear lamina plays an important role in the regulation of chromatin organization and gene positioning in animals. CROWDED NUCLEI (CRWN) is a strong candidate for the plant nuclear lamina protein in Arabidopsis thaliana but its biological function was largely unknown. Here, we show that CRWNs localize at the nuclear lamina and build the meshwork structure. Fluorescence in situ hybridization and RNA-seq analyses revealed that CRWNs regulate chromatin distribution and gene expression. More than 2000 differentially expressed genes were identified in the crwn1crwn4 double mutant. Copper-associated ( CA ) genes that form a gene cluster on chromosome 5 were among the downregulated genes in the double mutant exhibiting low tolerance to excess copper. Our analyses showed this low tolerance to copper was associated with the suppression of CA gene expression and that CRWN1 interacts with the CA gene locus, enabling the locus to localize at the nuclear lamina under excess copper conditions. The nuclear lamina regulates chromatin organization and gene positioning. Here the authors show that CROWDED NUCLEI proteins contribute to the meshwork lamina structure in Arabidopsis nuclei and regulate copper tolerance by promoting lamina association and expression of copper response genes.

The rhizome is a plant organ that develops from a shoot apical meristem but penetrates into belowground environments. To characterize the gene expression profile of rhizomes, we compared the rhizome transcriptome with those of the leaves, shoots and roots of a rhizomatous Brassicaceae plant, Cardamine leucantha. Overall, rhizome transcriptomes were characterized by the absence of genes that show rhizome-specific expression and expression profiles intermediate between those of shoots and roots. Our results suggest that both endogenous developmental factors and external environmental factors are important for controlling the rhizome transcriptome. Genes that showed relatively high expression in the rhizome compared to shoots and roots included those related to belowground defense, control of reactive oxygen species and cell elongation under dark conditions. A comparison of transcriptomes further allowed us to identify the presence of an ER body, a defense-related belowground organelle, in epidermal cells of the C. leucantha rhizome, which is the first report of ER bodies in rhizome tissue.

Oil bodies have multiple functions: oleosin-mediated freezing tolerance of seeds, direct interaction with glyoxysomes for lipid degradation in seedlings, and antifungal compound production in leaves.

Sterols are important lipid constituents of cellular membranes in plants and other organisms. Sterol homeostasis is under strict regulation in plants because excess sterols negatively impact plant growth. HIGH STEROL ESTER 1 (HISE1) functions as a negative regulator of sterol accumulation. If sterol production exceeds a certain threshold, excess sterols are detoxified via conversion to sterol esters by PHOSPHOLIPID STEROL ACYL TRANSFERASE 1 (PSAT1). We previously reported that the Arabidopsis thaliana double mutant hise1-3 psat1-2 shows 1.5-fold higher sterol content than the wild type and consequently a severe growth defect. However, the specific defects caused by excess sterol accumulation in plants remain unknown. In this study, we investigated the effects of excess sterols on plants by analyzing the phenotypes and transcriptomes of the hise1-3 psat1-2 double mutant. Transcriptomic analysis revealed that 435 genes were up-regulated in hise1-3 psat1-2 leaves compared with wild-type leaves. Gene ontology (GO) enrichment analysis revealed that abiotic and biotic stress-responsive genes including RESPONSIVE TO DESICCATION 29B/LOW-TEMPERATURE-INDUCED 65 (RD29B/LTI65) and COLD-REGULATED 15A (COR15A) were up-regulated in hise1-3 psat1-2 leaves compared with wild-type leaves. Expression levels of senescence-related genes were also much higher in hise1-3 psat1-2 leaves than in wild-type leaves. hise1-3 psat1-2 leaves showed early senescence, suggesting that excess sterols induce senescence of leaves. In the absence of sucrose, hise1-3 psat1-2 exhibited defects in seedling growth and root elongation. Together, our data suggest that excess sterol accumulation disrupts cellular activities of vegetative organs including leaves and roots, resulting in multiple damages to plants.

Leaf water isotopic composition is imprinted in several biomarkers of interest and it is imperative that we understand the isotopic enrichment of leaf water. Here, we test the effect of stomatal density and leaf water content on the oxygen isotopic composition of leaf water in transgenic Arabidopsis plants expressing different stomatal densities, and several other species showing a range of stomatal density. We grew Arabidopsis plants hydroponically and collected other species in the field. Stomatal density and leaf water content were determined for each plant. We measured transpiration and extracted leaf water for isotopic determination. Using these measurements and the current leaf water isotope model, we calculated several of the parameters related to leaf water isotopic enrichment. High stomatal density promoted leaf water isotope enrichment. No conclusion, however, can be drawn regarding the effect of leaf water content on leaf water isotope enrichment. Factors such as transpiration might mask the effect of stomatal density on leaf water isotopic enrichment. We propose a method by which stomatal density can be incorporated in the current Peclet model of leaf water isotope enrichment. These findings have important applications in the use of plant‐based metabolic proxies in paleoclimate studies.

Marchantia polymorpha is one of the model species of basal land plants. Although CRISPR/Cas9-based genome editing has already been demonstrated for this plant, the efficiency was too low to apply to functional analysis. In this study, we show the establishment of CRISPR/Cas9 genome editing vectors with high efficiency for both construction and genome editing. Codon optimization of Cas9 to Arabidopsis achieved over 70% genome editing efficiency at two loci tested. Systematic assessment revealed that guide sequences of 17 nt or shorter dramatically decreased this efficiency. We also demonstrated that a combinatorial use of this system and a floxed complementation construct enabled conditional analysis of a nearly essential gene. This study reports that simple, rapid, and efficient genome editing is feasible with the series of developed vectors.

Stomatal density ( ) is closely associated with photosynthetic and growth characteristics in plants. In the field, light intensity can fluctuate drastically within a day. The objective of the present study is to examine how higher affects stomatal conductance ( ) and CO assimilation rate ( ) dynamics, biomass production and water use under fluctuating light. Here, we compared the photosynthetic and growth characteristics under constant and fluctuating light among three lines of (L.): the wild type (WT), -overexpressing line (ST-OX), and knockout line ( ). ST-OX and showed 268.1 and 46.5% higher than WT ( < 0.05). Guard cell length of ST-OX was 10.0% lower than that of WT ( < 0.01). There were no significant variations in gas exchange parameters at steady state between WT and ST-OX or , although these parameters tended to be higher in ST-OX and than WT. On the other hand, ST-OX and showed faster induction than WT after step increase in light owing to the higher under initial dark condition. In addition, ST-OX and showed initially faster induction and, at the later phase, slower induction. Cumulative CO assimilation in ST-OX and was 57.6 and 78.8% higher than WT attributable to faster induction with reduction of water use efficiency ( ). yielded 25.6% higher biomass than WT under fluctuating light ( < 0.01). In the present study, higher resulted in faster photosynthetic induction owing to the higher initial . , with a moderate increase in , achieved greater biomass production than WT under fluctuating light. These results suggest that higher can be beneficial to improve biomass production in plants under fluctuating light conditions.