Enhancing the Corrosion Resistance Performance of Mg-1.8Zn-1.74Gd-0.5Y-0.4Zr Biomaterial via Solution Treatment Process.

: Microstructure and corrosion behavior of the solution-treated Mg-1.8Zn-1.74Gd-0.5Y-0.4Zr (wt%) alloy were studied. The results of microstructure indicated that the second phases of as-cast alloy was mainly comprised of Mg12Zn(Gd,Y) phase, Mg3Zn3(Gd,Y)2 phase and (Mg,Zn)3(Gd,Y) phase. After solution treatment process, the second phase gradually dissolved into the matrix, and the grain size increased. The effect of microgalvanic corrosion between α-Mg matrix and second phase was also improved. At the range of 470~510 °C solution treatment temperature, the corrosion resistance of the samples increases at first and then decreases slightly at 510 °C. All the solution-treated Mg-Zn-Gd-Y-Zr samples exhibit better corrosion resistance in comparison with as-cast sample. The existence form of the remaining phase affects the morphology of the corroded surface that relatively complete dissolution with homogeneous microstructure makes the sample more effective to obtain uniform corrosion form. The optimum temperature for solution treatment is 490 °C, which shows a much better corrosion resistance and uniform corrosion form after soaking for a long time.

Isolation, expression and functional analysis of a putative RNA-dependent RNA polymerase gene from maize (Zea mays L.).

RNA-dependent RNA polymerases (RdRPs) in plants have been reported to be involved in post-transcriptional gene silencing (PTGS) and antiviral defense. In this report, an RdRP gene from maize (ZmRdRP1) was obtained by rapid amplification of cDNA ends (RACE) and RT-PCR. The mRNA of ZmRdRP1 was composed of 3785 nucleotides, including a 167 nt 5' untranslated region (UTR), a 291 nt 3'UTR and a 3327 nt open reading frame (ORF), which encodes a putative protein of 1108 amino acids with an estimated molecular mass of 126.9 kDa and a predicated isoelectric point (pI) of 8.37. Real-time quantitative RT-PCR analysis showed that ZmRdRP1 was elicited by salicylic acid (SA) treatment, methyl jasmonate (MeJA) treatment and sugarcane mosaic virus (SCMV) infection. We silenced ZmRdRP1 by constitutively expressing an inverted-repeat fragment of ZmRdRP1 (ir-RdRP1) in transgenic maize plants. Further studies revealed that the ir-RdRP1 transgenic plants were more susceptible to SCMV infection than wild type plants. Virus-infected transgenic maize plants developed more serious disease symptoms and accumulated more virus than wild type plants. These findings suggested that ZmRdRP1 was involved in antiviral defense in maize.

An F-box gene, CPR30, functions as a negative regulator of the defense response in Arabidopsis.

Arabidopsis gain-of-resistance mutants, which show HR-like lesion formation and SAR-like constitutive defense responses, were used well as tools to unravel the plant defense mechanisms. We have identified a novel mutant, designated constitutive expresser of PR genes 30 (cpr30), that exhibited dwarf morphology, constitutive resistance to the bacterial pathogen Pseudomonas syringae and the dramatic induction of defense-response gene expression. The cpr30-conferred growth defect morphology and defense responses are dependent on ENHANCED DISEASE SUSCEPTIBILITY 1 (EDS1), PHYTOALEXIN DEFICIENT 4 (PAD4), and NONRACE-SPECIFIC DISEASE RESISTANCE 1 (NDR1). Further studies demonstrated that salicylic acid (SA) could partially account for the cpr30-conferred constitutive PR1 gene expression, but not for the growth defect, and that the cpr30-conferred defense responses were NPR1 independent. We observed a widespread expression of CPR30 throughout the plant, and a localization of CPR30-GFP fusion protein in the cytoplasm and nucleus. As an F-box protein, CPR30 could interact with multiple Arabidopsis-SKP1-like (ASK) proteins in vivo. Co-localization of CPR30 and ASK1 or ASK2 was observed in Arabidopsis protoplasts. Based on these results, we conclude that CPR30, a novel negative regulator, regulates both SA-dependent and SA-independent defense signaling, most likely through the ubiquitin-proteasome pathway in Arabidopsis.

Cloning and characterization of a novel CBL-interacting protein kinase from maize.

A novel CBL-interacting protein kinase (CIPK) gene, ZmCIPK16, was isolated from maize (Zea mays), which has been certified to have two copies in the genome. The ZmCIPK16 is strongly induced in maize seedlings by PEG, NaCl, ABA, dehydration, heat and drought, but not by cold. A yeast two-hybrid assay demonstrated that ZmCIPK16 interacted with ZmCBL3, ZmCBL4, ZmCBL5, and ZmCBL8. Bimolecular fluorescence complementation (BiFC) assays prove that ZmCIPK16 can interact with ZmCBL3, ZmCBL4, ZmCBL5, and ZmCBL8 in vivo. Subcellular localization showed that ZmCIPK16 is distributed in the nucleus, plasma membrane and cytoplasm; this is different from the specific localization of ZmCBL3, ZmCBL4, and ZmCBL5, which are found in the plasma membrane. The results also showed that overexpression of ZmCIPK16 in the Arabidopsis sos2 mutant induced the expression of the SOS1 gene and enhanced salt tolerance. These findings indicate that ZmCIPK16 may be involved in the CBL-CIPK signaling network in maize responses to salt stress.

Cloning and characterization of the SnRK2 gene family from Zea mays.

The SnRK2 gene family is a group of plant-specific protein kinases that has been implicated in ABA and abiotic stress signaling. We found 11 SnRK2s in maize, assigned names from ZmSnRK2.1 to ZmSnRK2.11 and cloned ten of them. By analyzing the gene structure of all the SnRK2s from Arabidopsis, rice, and maize, we found seven exons that were conserved in length among most of the SnRK2s. Although the C-terminus was divergent, we found seven conserved motifs. Of these, motif 1 was common to all of the SnRK2 genes. Based on phylogenetic analysis using the kinase domain and motif 1, the SnRK2s were divided into three groups. Motifs 4 and 5 were found specifically in group I, and many genes of this group have been confirmed to be induced by ABA. This result suggests that these two motifs mediate the ABA response. The expression patterns of ZmSnRK2 genes were characterized by using quantitative real-time RCR, which revealed that ZmSnRK2 genes were induced by one or more abiotic stress treatments and therefore may play important roles in maize stress responses.