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.

[Three-dimensional finite element analysis of the influence of different implant-abutment joint design on abutment and abutment screw stress].

PURPOSE: This experiment studied the influence of different connection designs of the tapered retention and platform transfer implant on the stress of the abutments and abutment screws. METHODS: Implant models (Platform-switching: 0.2, 0.4, 0.6, 0.8, 1.0 mm; Taper:6°,8°,10°) were established, and Von-mises stress and strain of abutment and abutment screw under different loads were analyzed. RESULTS: With the increase of the platform-switching amount, the peak von-Mises stress and strain of abutment and abutment screw increased. The peak von-Mises stress of the model with platform transfer≥0.8 mm was higher than 690 MPa. In addition, the variation amplitude was horizontal loading>oblique loading>vertical loading. The maximum stress of the abutment was concentrated at the neck of the abutment in 81.67% models. The stress of the abutment screw was concentrated at the turning point of the head and body of abutment screw in all models. CONCLUSIONS: The increase of the amount of platform switching makes the abutment and the abutment screws bear more force in the occlusion process. Therefore, in order to reduce the occurrence of mechanical complications after implantation and restoration, the implant system with the minimum amount of platform transfer should be selected within a certain range. The maximum stress on the abutments and screws exceeds the yield strength of pure titanium in implants with platform-switching amount greater than 0.8 mm, indicating that this design should be selected prudently in clinical practice.

[Study on the friction and wear properties of fluorapatite glass ceramics, feldspathic porcelain and natural tooth].

PURPOSE: The purpose of this study was to observe the friction and wear characteristics of dental fluorapatite glass ceramics, feldspathic porcelain and natural tooth in dry friction and saliva lubrication. METHODS: Two kinds of veneering porcelain (IPS-emaxcream and Vita vm9) coated zirconia-decorative porcelain double-layer material sample were prepared (size 20 mm × 20 mm × 4.5 mm), each group had 20 specimens. Friction and wear tests were carried out on 2 kinds of zirconia-decorative porcelain sample under dry friction and saliva accompanying environment respectively by setting different sizes of vertical load and sliding frequency using MMV-1 friction and wear testing machine. SPSS 17.0 software package was used for one-way ANOVA and t test to determine whether there were differences in friction coefficient and wear amount between two groups. RESULTS: The dynamic friction coefficient and wear amount of fluorapatite glass ceramics under saliva lubrication condition were significantly greater than those under dry friction condition. On the contrary to fluorapatite glass ceramics, the dynamic friction coefficient and wear amount of feldspathic decorative ceramics under dry friction condition were significantly greater than those under saliva lubrication condition. Under dry friction and saliva lubrication, the wear amount of fluorapatite glass ceramics was significantly smaller than that of feldspathic decorative ceramics. Scanning electron microscopy showed that under saliva lubrication condition, fluorapatite glass ceramics and the corresponding natural teeth had more severe wear surface than dry friction. Under dry friction condition, feldspathic decorative porcelain and corresponding natural teeth wear more seriously than fluorapatite glass ceramic, and the difference in saliva lubrication condition was relatively small. CONCLUSIONS: Compared with feldspathic decorative porcelain, fluorapatite glass ceramics and natural teeth shows superior wear resistance under dry friction condition. The addition of saliva can reduce the difference between the friction and wear performance of the two decorative porcelains.

The Transcription Factor AtDOF4.7 Is Involved in Ethylene- and IDA-Mediated Organ Abscission in Arabidopsis.

Organ abscission is an important plant developmental process that occurs in response to environmental stress or pathogens. In Arabidopsis, ligand signals, such as ethylene or INFLORESCENCE DEFICIENT IN ABSCISSION (IDA), can regulate organ abscission. Previously, we reported that overexpression of AtDOF4.7, a transcription factor gene, directly suppresses the expression of the abscission-related gene ARABIDOPSIS DEHISCENCE ZONE POLYGALACTURONASE 2 (ADPG2), resulting in a deficiency of floral organ abscission. However, the relationship between AtDOF4.7 and abscission pathways still needs to be investigated. In this study, we showed that ethylene regulates the expression of AtDOF4.7, and the peptide ligand, IDA negatively regulates AtDOF4.7 at the transcriptional level. Genetic evidence indicates that AtDOF4.7 and IDA are involved in a common pathway, and a MAPK cascade can phosphorylate AtDOF4.7 in vitro. Further in vivo data suggest that AtDOF4.7 protein levels may be regulated by this phosphorylation. Collectively, our results indicate that ethylene regulates AtDOF4.7 that is involved in the IDA-mediated floral organ abscission pathway.