GR1 and NTRA involved in pollen tube growth in the stigma of Arabidopsis.

MAIN CONCLUSION: Arabidopsis GR1 and NTRA function in pollen tube penetrating the stigma into the transmitting tract during pollination. During pollination, recognition between pollen (tube) and stigma mediates the hydration and germination of pollen, as well as the growth of the pollen tube on the stigma. Arabidopsis glutathione reductase 1 (GR1) and NADPH-dependent thioredoxin reductase A (NTRA) are involved in regulating cell redox hemostasis. Both GR1 and NTRA are expressed in pollen, but their roles in pollen germination and the growth of the pollen tube need further investigation. In this study, we performed pollination experiments and found that the Arabidopsis gr1/ + ntra/- and gr1/- ntra/ + double mutation compromised the transmission of male gametophytes. Pollen morphology and viability of the mutants did not show obvious abnormalities. Additionally, the pollen hydration and germination of the double mutants on solid pollen germination medium were comparable to those of the wild type. However, the pollen tubes with gr1 ntra double mutation were unable to penetrate the stigma and enter the transmitting tract when they grew on the surface of the stigma. Our results indicate that GR1 and NTRA play a role in regulating the interaction between the pollen tube and the stigma during pollination.

PALD encoding a lipid droplet-associated protein is critical for the accumulation of lipid droplets and pollen longevity in Arabidopsis.

Pollen longevity is critical for plant pollination and hybrid seed production, but few studies have focused on pollen longevity. In this study, we identified an Arabidopsis thaliana gene, Protein associated with lipid droplets (PALD), which is strongly expressed in pollen and critical for the regulation of pollen longevity. PALD was expressed specifically in mature pollen grains and the pollen tube, and its expression was upregulated under dry conditions. PALD encoded a lipid droplet (LD)-associated protein and its N terminus was critical for the LD localization of PALD. The number of LDs and diameter were reduced in pollen grains of the loss-of-function PALD mutants. The viability and germination of the mature pollen grains of the pald mutants were comparable with those of the wild-type, but after the pollen grains were stored under dry conditions, pollen germination and male transmission of the mutant were compromised compared with those of the wild-type. Our study suggests that PALD was required for the maintenance of LD quality in mature pollen grains and regulation of pollen longevity.

Pollen-specific gene SKU5-SIMILAR 13 enhances growth of pollen tubes in the transmitting tract in Arabidopsis.

Pollen tube growth and penetration in female tissues are essential for the transfer of sperm to the embryo sac during plant pollination. Despite its importance during pollination, little is known about the mechanisms that mediate pollen tube growth in female tissues. In this study, we identified an Arabidopsis thaliana pollen/pollen tube-specific gene, SKU5-SIMILAR 13 (SKS13), which was critical for the growth of pollen tubes in the transmitting tract. The SKS13 protein was distributed throughout the cytoplasm and pollen tube walls at the apical region. In comparison with wild-type pollen tubes, those of the sks13 mutants burst more frequently when grown in vitro. Additionally, the growth of sks13 pollen tubes was retarded in the transmitting tract, thereby resulting in decreased male fertility. The accumulation of pectin and cellulose in the cell wall of sks13 pollen tubes was altered, and the content of jasmonic acid (JA) in sks13 pollen was reduced. The pollen tubes treated with an inhibitor of JA biosynthesis grew much more slowly and had an altered distribution of pectin, which is similar to the pollen tube phenotypes of the SKS13 mutation. Our results suggest that SKS13 is essential for pollen tube growth in the transmitting tract by mediating the biosynthesis of JA that modifies the components of pollen tube cell walls.

Down-expression of TaPIN1s Increases the Tiller Number and Grain Yield in Wheat.

BACKGROUND: Tiller number is a factor determining panicle number and grain yield in wheat (Triticum aestivum). Auxin plays an important role in the regulation of branch production. PIN-FORMED 1 (PIN1), an auxin efflux carrier, plays a role in the regulation of tiller number in rice (Oryza sativa); however, little is known on the roles of PIN1 in wheat. RESULTS: Nine homologs of TaPIN1 genes were identified in wheat, of which TaPIN1-6 genes showed higher expression in the stem apex and young leaf in wheat, and the TaPIN1-6a protein was localized in the plasma membrane. The down-expression of TaPIN1s increased the tiller number in TaPIN1-RNA interference (TaPIN1-RNAi) transgenic wheat plants, indicating that auxin might mediate the axillary bud production. By contrast, the spikelet number, grain number per panicle, and the 1000-grain weight were decreased in the TaPIN1-RNAi transgenic wheat plants compared with those in the wild type. In summary, a reduction of TaPIN1s expression increased the tiller number and grain yield per plant of wheat. CONCLUSIONS: Phylogenetic analysis and protein structure of nine TaPIN1 proteins were analyzed, and subcellular localization of TaPIN1-6a was located in the plasma membrane. Knock-down expression of TaPIN1 genes increased the tiller number of transgenic wheat lines. Our study suggests that TaPIN1s is required for the regulation of grain yield in wheat.

Glycosylphosphatidylinositol-anchored proteins mediate the interactions between pollen/pollen tube and pistil tissues.

In flowering plants, pollen germination on the stigma and pollen tube growth in pistil tissues are critical for sexual plant reproduction, which are involved in the interactions between pollen/pollen tube and pistil tissues. GPI-anchored proteins (GPI-APs) are located on the external surface of the plasma membrane and function in various processes of sexual plant reproduction. The evidences suggest that GPI-APs participate in endosome machinery, Ca2+ oscillations, the development of the transmitting tract, the maintenance of the integrity of pollen tube, the enhancement of interactions of the receptor-like kinase (RLK) and ligand, and guidance of the growth of pollen tube, and so on. In this review, we will summarize the recent progress on the roles of GPI-APs in the interactions between pollen/pollen tube and pistil tissues during pollination, such as pollen germination on the stigma, pollen tube growth in the transmitting tract, pollen tube guidance to the ovule, and pollen tube reception in the embryo sac. We will also discuss the future outlook of GPI-APs in the interactions between pollen/pollen tube and pistil tissues.

Arabidopsis AtPRP17 functions in embryo development by regulating embryonic patterning.

MAIN CONCLUSION: Arabidopsis AtPRP17, a homolog of yeast splicing factor gene PRP17, is expressed in siliques and embryos and functions in embryo development via regulating embryonic patterning. Yeast splicing factor PRP17/CDC40 is essential for cell growth through involvement in cell cycle regulation. Arabidopsis genome encodes a homolog of PRP17, AtPRP17; however, its function in Arabidopsis development is unknown. This study showed that AtPRP17 was highly expressed in siliques and embryos, and the protein was localized in the nucleus. The loss-of-function mutation of AtPRP17 led to shrunken seeds in Arabidopsis mature siliques. Further analysis revealed that the defective mature seeds of the mutant resulted from abnormal embryos with shriveled cotyledons, unequal cotyledons, swollen and shortened hypocotyls, or shortened radicles. During embryogenesis, mutant embryos showed delayed development and defective patterning of the apical and base domains, such as inhibited cotyledons and disorganized quiescent center cells and columella. Our results suggested that AtPRP17 functions in Arabidopsis embryo development via regulating embryonic patterning.

Genome-wide identification and expression analysis of YTH domain-containing RNA-binding protein family in common wheat.

BACKGROUND: N6-Methyladenosine (m6A) is the most widespread RNA modification that plays roles in the regulation of genes and genome stability. YT521-B homology (YTH) domain-containing RNA-binding proteins are important RNA binding proteins that affect the fate of m6A-containing RNA by binding m6A. Little is known about the YTH genes in common wheat (Triticum aestivum L.), one of the most important crops for humans. RESULTS: A total of 39 TaYTH genes were identified in common wheat, which are comprised of 13 homologous triads, and could be mapped in 18 out of the 21 chromosomes. A phylogenetic analysis revealed that the TaYTHs could be divided into two groups: YTHDF (TaDF) and YTHDC (TaDC). The TaYTHs in the same group share similar motif distributions and domain organizations, which indicates functional similarity between the closely related TaYTHs. The TaDF proteins share only one domain, which is the YTH domain. In contrast, the TaDCs possess three C3H1-type zinc finger repeats at their N-termini in addition to their central YTH domain. In TaDFs, the predicated aromatic cage pocket that binds the methylysine residue of m6A is composed of tryptophan, tryptophan, and tryptophan (WWW). In contrast, the aromatic cage pocket in the TaDCs is composed of tryptophan, tryptophan, and tyrosine (WWY). In addition to the general aspartic acid or asparagine residue used to form a hydrogen bond with N1 of m6A, histidine might be utilized in some TaDFb proteins. An analysis of the expression using both online RNA-Seq data and quantitative real-time PCR verification revealed that the TaDFa and TaDFb genes are highly expressed in various tissues/organs compared with that of TaDFcs and TaDCs. In addition, the expression of the TaYTH genes is changed in response to various abiotic stresses. CONCLUSIONS: In this study, we identified 39 TaYTH genes from common wheat. The phylogenetic structure, chromosome distribution, and patterns of expression of these genes and their protein structures were analyzed. Our results provide a foundation for the functional analysis of TaYTHs in the future.

The Arabidopsis KINßγ Subunit of the SnRK1 Complex Regulates Pollen Hydration on the Stigma by Mediating the Level of Reactive Oxygen Species in Pollen.

Pollen-stigma interactions are essential for pollen germination. The highly regulated process of pollen germination includes pollen adhesion, hydration, and germination on the stigma. However, the internal signaling of pollen that regulates pollen-stigma interactions is poorly understood. KINßγ is a plant-specific subunit of the SNF1-related protein kinase 1 complex which plays important roles in the regulation of plant development. Here, we showed that KINßγ was a cytoplasm- and nucleus-localized protein in the vegetative cells of pollen grains in Arabidopsis. The pollen of the Arabidopsis kinßγ mutant could not germinate on stigma, although it germinated normally in vitro. Further analysis revealed the hydration of kinßγ mutant pollen on the stigma was compromised. However, adding water to the stigma promoted the germination of the mutant pollen in vivo, suggesting that the compromised hydration of the mutant pollen led to its defective germination. In kinßγ mutant pollen, the structure of the mitochondria and peroxisomes was destroyed, and their numbers were significantly reduced compared with those in the wild type. Furthermore, we found that the kinßγ mutant exhibited reduced levels of reactive oxygen species (ROS) in pollen. The addition of H2O2 in vitro partially compensated for the reduced water absorption of the mutant pollen, and reducing ROS levels in pollen by overexpressing Arabidopsis CATALASE 3 resulted in compromised hydration of pollen on the stigma. These results indicate that Arabidopsis KINßγ is critical for the regulation of ROS levels by mediating the biogenesis of mitochondria and peroxisomes in pollen, which is required for pollen-stigma interactions during pollination.

Arabidopsis shaker pollen inward K+ channel SPIK functions in SnRK1 complex-regulated pollen hydration on the stigma.

Pollen hydration is a critical step that determines pollen germination on the stigma. KINßγ is a plant-specific subunit of the SNF1-related protein kinase 1 complex (SnRK1 complex). In pollen of the Arabidopsis kinßγ mutant, the levels of reactive oxygen species were decreased which lead to compromised hydration of the mutant pollen on the stigma. In this study, we analyzed gene expression in kinßγ mutant pollen by RNA-seq and found the expression of inward shaker K+ channel SPIK was down-regulated in the kinßγ pollen. Furthermore, we showed that the pollen hydration of the Arabidopsis spik mutant was defective on the wild-type stigma, although the mutant pollen demonstrated normal hydration in vitro. Additionally, the defective hydration of spik mutant pollen could not be rescued by the wild-type pollen on the stigma, indicating that the spik mutation deprived the capability of pollen absorption on the stigma. Our results suggest that the Arabidopsis SnRK1 complex regulates SPIK expression, which functions in determining pollen hydration on the stigma.

Interaction between RNA helicase ROOT INITIATION DEFECTIVE 1 and GAMETOPHYTIC FACTOR 1 is involved in female gametophyte development in Arabidopsis.

ROOT INITIATION DEFECTIVE 1 (RID1) is an Arabidopsis DEAH/RHA RNA helicase. It functions in hypocotyl de-differentiation, de novo meristem formation, and cell specification of the mature female gametophyte (FG). However, it is unclear how RID1 regulates FG development. In this study, we observed that mutations to RID1 disrupted the developmental synchrony and retarded the progression of FG development. RID1 exhibited RNA helicase activity, with a preference for unwinding double-stranded RNA in the 3' to 5' direction. Furthermore, we found that RID1 interacts with GAMETOPHYTIC FACTOR 1 (GFA1), which is an integral protein of the spliceosome component U5 small nuclear ribonucleoprotein (snRNP) particle. Substitution of specific RID1 amino acids (Y266F and T267I) inhibited the interaction with GFA1. In addition, the mutated RID1 could not complement the seed-abortion phenotype of the rid1 mutant. The rid1 and gfa1 mutants exhibited similar abnormalities in pre-mRNA splicing and down-regulated expression of some genes involved in FG development. Our results suggest that an interaction between RID1 and the U5 snRNP complex regulates essential pre-mRNA splicing of the genes required for FG development. This study provides new information regarding the mechanism underlying the FG developmental process.

ABNORMAL POLLEN TUBE GUIDANCE1, an Endoplasmic Reticulum-Localized Mannosyltransferase Homolog of GLYCOSYLPHOSPHATIDYLINOSITOL10 in Yeast and PHOSPHATIDYLINOSITOL GLYCAN ANCHOR BIOSYNTHESIS B in Human, Is Required for Arabidopsis Pollen Tube Micropylar Guidance and Embryo Development.

The perception and response of pollen tubes to the female guidance signals are crucial for directional pollen tube growth inside female tissues, which leads to successful reproduction. In pursuing the mechanisms underlying this biological process, we identified the Arabidopsis (Arabidopsis thaliana) abnormal pollen tube guidance1 (aptg1) mutant, whose pollen tubes showed compromised micropylar guidance. In addition to its male defect, the aptg1 mutant showed embryo lethality. APTG1 encodes a putative mannosyltransferase homolog to human PHOSPHATIDYLINOSITOL GLYCAN ANCHOR BIOSYNTHESIS B and yeast (Saccharomyces cerevisiae) GLYCOSYLPHOSPHATIDYLINOSITOL10 (GPI10), both of which are involved in the biosynthesis of GPI anchors. We found that APTG1 was expressed in most plant tissues, including mature pollen, pollen tubes, mature embryo sacs, and developing embryos. By fluorescence colabeling, we showed that APTG1 was localized in the endoplasmic reticulum, where GPI anchors are synthesized. Disruption of APTG1 affected the localization of COBRA-LIKE10, a GPI-anchored protein important for pollen tube growth and guidance. The results shown here demonstrate that APTG1 is involved in both vegetative and reproductive development in Arabidopsis, likely through processing and proper targeting of GPI-anchored proteins.

Identification of small secreted peptides (SSPs) in maize and expression analysis of partial SSP genes in reproductive tissues.

MAIN CONCLUSION: Maize 1,491 small secreted peptides were identified, which were classified according to the character of peptide sequences. Partial SSP gene expressions in reproductive tissues were determined by qRT-PCR. Small secreted peptides (SSPs) are important cell-cell communication messengers in plants. Most information on plant SSPs come from Arabidopsis thaliana and Oryza sativa, while little is known about the SSPs of other grass species such as maize (Zea mays). In this study, we identified 1,491 SSP genes from maize genomic sequences. These putative SSP genes were distributed throughout the ten maize chromosomes. Among them, 611 SSPs were classified into 198 superfamilies according to their conserved domains, and 725 SSPs with four or more cysteines at their C-termini shared similar cysteine arrangements with their counterparts in other plant species. Moreover, the SSPs requiring post-translational modification, as well as defensin-like (DEFL) proteins, were identified. Further, the expression levels of 110 SSP genes were analyzed in reproductive tissues, including male flower, pollen, silk, and ovary. Most of the genes encoding basal-layer antifungal peptide-like, small coat proteins-like, thioredoxin-like proteins, γ-thionins-like, and DEFL proteins showed high expression levels in the ovary and male flower compared with their levels in silk and mature pollen. The rapid alkalinization factor-like genes were highly expressed only in the mature ovary and mature pollen, and pollen Ole e 1-like genes showed low expression in silk. The results of this study provide basic information for further analysis of SSP functions in the reproductive process of maize.

The reorganization of actin filaments is required for vacuolar fusion of guard cells during stomatal opening in Arabidopsis.

The reorganization of actin filaments (AFs) and vacuoles in guard cells is involved in the regulation of stomatal movement. However, it remains unclear whether there is any interaction between the reorganization of AFs and vacuolar changes during stomatal movement. Here, we report the relationship between the reorganization of AFs and vacuolar fusion revealed in pharmacological experiments, and characterizing stomatal opening in actin-related protein 2 (arp2) and arp3 mutants. Our results show that cytochalasin-D-induced depolymerization or phalloidin-induced stabilization of AFs leads to an increase in small unfused vacuoles during stomatal opening in wild-type (WT) Arabidopsis plants. Light-induced stomatal opening is retarded and vacuolar fusion in guard cells is impaired in the mutants, in which the reorganization and the dynamic parameters of AFs are aberrant compared with those of the WT. In WT, AFs tightly surround the small separated vacuoles, forming a ring that encircles the boundary membranes of vacuoles partly fused during stomatal opening. In contrast, in the mutants, most AFs and actin patches accumulate abnormally around the nuclei of the guard cells, which probably further impair vacuolar fusion and retard stomatal opening. Our results suggest that the reorganization of AFs regulates vacuolar fusion in guard cells during stomatal opening.

Genome-edited TaTFL1-5 mutation decreases tiller and spikelet numbers in common wheat.

Tillering is a critical agronomic trait of wheat (Triticum aestivum L.) that determines the shoot architecture and affects grain yield. TERMINAL FLOWER 1 (TFL1), encoding a phosphatidylethanolamine-binding protein, is implicated in the transition to flowering and shoot architecture in plant development. However, the roles of TFL1 homologs is little known in wheat development. CRISPR/Cas9-mediated targeted mutagenesis was used in this study to generate a set of wheat (Fielder) mutants with single, double or triple-null tatfl1-5 alleles. The wheat tatfl1-5 mutations decreased the tiller number per plant in the vegetative growth stage and the effective tiller number per plant and spikelet number per spike at maturity in the field. RNA-seq analysis showed that the expression of the auxin signaling-related and cytokinin signaling-related genes was significantly changed in the axillary buds of tatfl1-5 mutant seedlings. The results suggested that wheat TaTFL1-5s were implicated in tiller regulation by auxin and cytokinin signaling.

Comparative proteomic analysis reveals similar and distinct features of proteins in dry and wet stigmas.

Angiosperm stigma supports compatible pollen germination and tube growth, resulting in fertilization and seed production. Stigmas are mainly divided into two types, dry and wet, according to the absence or presence of exudates on their surfaces. Here, we used 2DE and MS to identify proteins specifically and preferentially expressed in the stigmas of maize (Zea Mays, dry stigma) and tobacco (Nicotiana tabacum, wet stigma), as well as proteins rinsed from the surface of the tobacco stigma. We found that the specifically and preferentially expressed proteins in maize and tobacco stigmas share similar distributions in functional categories. However, these proteins showed important difference between dry and wet stigmas in a few aspects, such as protein homology in "signal transduction" and "lipid metabolism," relative expression levels of proteins containing signal peptides and proteins in "defense and stress response." These different features might be related to the specific structures and functions of dry and wet stigmas. The possible roles of some stigma-expressed proteins were discussed. Our results provide important information on functions of proteins in dry and wet stigmas and reveal aspects of conservation and divergence between dry and wet stigmas at the proteomic level.

Identification of genes specifically or preferentially expressed in maize silk reveals similarity and diversity in transcript abundance of different dry stigmas.

BACKGROUND: In plants, pollination is a critical step in reproduction. During pollination, constant communication between male pollen and the female stigma is required for pollen adhesion, germination, and tube growth. The detailed mechanisms of stigma-mediated reproductive processes, however, remain largely unknown. Maize (Zea mays L.), one of the world's most important crops, has been extensively used as a model species to study molecular mechanisms of pollen and stigma interaction. A comprehensive analysis of maize silk transcriptome may provide valuable information for investigating stigma functionality. A comparative analysis of expression profiles between maize silk and dry stigmas of other species might reveal conserved and diverse mechanisms that underlie stigma-mediated reproductive processes in various plant species. RESULTS: Transcript abundance profiles of mature silk, mature pollen, mature ovary, and seedling were investigated using RNA-seq. By comparing the transcriptomes of these tissues, we identified 1,427 genes specifically or preferentially expressed in maize silk. Bioinformatic analyses of these genes revealed many genes with known functions in plant reproduction as well as novel candidate genes that encode amino acid transporters, peptide and oligopeptide transporters, and cysteine-rich receptor-like kinases. In addition, comparison of gene sets specifically or preferentially expressed in stigmas of maize, rice (Oryza sativa L.), and Arabidopsis (Arabidopsis thaliana [L.] Heynh.) identified a number of homologous genes involved either in pollen adhesion, hydration, and germination or in initial growth and penetration of pollen tubes into the stigma surface. The comparison also indicated that maize shares a more similar profile and larger number of conserved genes with rice than with Arabidopsis, and that amino acid and lipid transport-related genes are distinctively overrepresented in maize. CONCLUSIONS: Many of the novel genes uncovered in this study are potentially involved in stigma-mediated reproductive processes, including genes encoding amino acid transporters, peptide and oligopeptide transporters, and cysteine-rich receptor-like kinases. The data also suggest that dry stigmas share similar mechanisms at early stages of pollen-stigma interaction. Compared with Arabidopsis, maize and rice appear to have more conserved functional mechanisms. Genes involved in amino acid and lipid transport may be responsible for mechanisms in the reproductive process that are unique to maize silk.

Disrupted actin dynamics trigger an increment in the reactive oxygen species levels in the Arabidopsis root under salt stress.

UNLABELLED: Changes in actin dynamics represent the primary response of the plant cell to extracellular signaling. Recent studies have now revealed that actin remodeling is involved in abiotic stress tolerance in plants. In our current study, the relationship between the changes in actin dynamics and the reactive oxygen species (ROS) level at the initial stages of salt stress was investigated in the elongation zone of the Arabidopsis root tip. We found that a 200 mM NaCl treatment disrupted the dynamics of the actin filaments within 10 min and increased the ROS levels in the elongation zone cells of the Arabidopsis root tip. We further found that the NADPH oxidase activity inhibitor, diphenyleneiodonium, treatment blocked this ROS increase under salt stress conditions. The roles of actin dynamics and the NADPH oxidases in ROS generation were further analyzed using the actin-specific agents, latrunculin B (Lat-B) and jasplakinolide (Jasp), and mutants of Arabidopsis NADPH oxidase AtrbohC. Lat-B and Jasp promote actin depolymerization and polymerization, respectively, and both were found to enhance the ROS levels following NaCl treatment. However, this response was abolished in the atrbohC mutants. Our present results thus demonstrate that actin dynamics are involved in regulating the ROS level in Arabidopsis root under salt stress conditions. KEY MESSAGE: Salt stress disrupts the dynamics of the actin filaments in Arabidopsis in the short term which are involved in regulating the ROS levels that arise under salt stress conditions via the actions of the AtrbohC.

Arabidopsis AtVPS15 is essential for pollen development and germination through modulating phosphatidylinositol 3-phosphate formation.

Arabidopsis thaliana phosphatidylinositol 3-kinase (AtVPS34) functions in the development and germination of pollen by catalyzing the biosynthesis of phosphatidylinositol 3-phosphate (PI3P). In yeast, Vps15p is required for the membrane targeting and activity of Vps34. The expression of Arabidopsis thaliana VPS15 (AtVPS15), an ortholog of yeast Vps15, is mainly detected in pollen grains and pollen tubes. To determine its role in pollen development and pollen tube growth, we attempted to isolate the T-DNA insertion mutants of AtVPS15; however, homozygous lines of atvps15 were not obtained from the progeny of atvps15/+ heterozygotes. Genetic analysis revealed that the abnormal segregation is due to the failure of transmission of the atvps15 allele through pollen. Most pollen grains from the atvps15/+ genotype are viable, with normal exine structure and nuclei, but some mature pollen grains are characterized with unusual large vacuoles that are not observed in pollen grains from the wild AtVPS15 genotype. The germination ratio of pollen from the atvps15/+ genotype is about half when compared to that from the wild AtVPS15 genotype. When supplied with PI3P, in vitro pollen germination of the atvps15/+ genotype is greatly improved. Presumably, AtVPS15 functions in pollen development and germination by regulating PI3P biosynthesis in Arabidopsis.

Overexpression of AtDOF4.7, an Arabidopsis DOF family transcription factor, induces floral organ abscission deficiency in Arabidopsis.

After flower pollination, a programmed process called abscission occurs in which unwanted floral organs are actively shed from the main plant body. We found that a member of the DOF (for DNA binding with one finger) transcription factor family, Arabidopsis (Arabidopsis thaliana) DOF4.7, was expressed robustly in the abscission zone. The Arabidopsis 35S::AtDOF4.7 lines with constitutive expression of AtDOF4.7 exhibited an ethylene-independent floral organ abscission deficiency. In these lines, anatomical analyses showed that the formation of the abscission zone was normal. However, dissolution of the middle lamella failed to separate between the cell walls. AtDOF4.7 was identified as a nucleus-localized transcription factor. This protein had both in vitro and in vivo binding activity to typical DOF cis-elements in the promoter of an abscission-related polygalacturonase (PG) gene, PGAZAT. Overexpression of AtDOF4.7 resulted in down-regulation of PGAZAT. AtDOF4.7 interacted with another abscission-related transcription factor, Arabidopsis ZINC FINGER PROTEIN2. Taken together, our results suggest that AtDOF4.7 participates in the control of abscission as part of the transcription complex that directly regulates the expression of cell wall hydrolysis enzymes.

Stochastic dynamics of actin filaments in guard cells regulating chloroplast localization during stomatal movement.

Actin filaments and chloroplasts in guard cells play roles in stomatal function. However, detailed actin dynamics vary, and the roles that they play in chloroplast localization during stomatal movement remain to be determined. We examined the dynamics of actin filaments and chloroplast localization in transgenic tobacco expressing green fluorescent protein (GFP)-mouse talin in guard cells by time-lapse imaging. Actin filaments showed sliding, bundling and branching dynamics in moving guard cells. During stomatal movement, long filaments can be severed into small fragments, which can form longer filaments by end-joining activities. With chloroplast movement, actin filaments near chloroplasts showed severing and elongation activity in guard cells during stomatal movement. Cytochalasin B treatment abolished elongation, bundling and branching activities of actin filaments in guard cells, and these changes of actin filaments, and as a result, more chloroplasts were localized at the centre of guard cells. However, chloroplast turning to avoid high light, and sliding of actin fragments near the chloroplast, was unaffected following cytochalasin B treatment in guard cells. We suggest that the sliding dynamics of actin may play roles in chloroplast turning in guard cells. Our results indicate that the stochastic dynamics of actin filaments in guard cells regulate chloroplast localization during stomatal movement.