Synthesis of Nitrogen and Phosphorus/Sulfur Co-Doped Carbon Xerogels for the Efficient Electrocatalytic Reduction of p-Nitrophenol.

Carbon xerogels co-doped with nitrogen (N) and phosphorus (P) or sulfur (S) were synthesized and employed as catalysts for the electrocatalytic reduction of p-nitrophenol (p-NP). The materials were prepared by first synthesizing N-doped carbon xerogels (NDCX) via the pyrolysis of organic gels, and then introducing P or S atoms to the NDCX by a vapor deposition method. The materials were characterized by various measurements including X-ray diffraction, N2 physisorption, Transmission electron microscopy, Fourier Infrared spectrometer, and X-ray photoelectron spectra, which showed that N atoms were successfully doped to the carbon xerogels, and the co-doping of P or S atoms affected the existing status of N atoms. Cyclic voltammetry (CV) scanning manifested that the N and P co-doped materials, i.e., P-NDCX-1.0, was the most suitable catalyst for the reaction, showing an overpotential of -0.569 V (vs. Ag/AgCl) and a peak slop of 695.90 µA/V. The material was also stable in the reaction and only a 14 mV shift in the reduction peak overpotential was observed after running for 100 cycles.

Earlier Degraded Tapetum1 (EDT1) Encodes an ATP-Citrate Lyase Required for Tapetum Programmed Cell Death.

In flowering plants, the tapetum cells in anthers undergo programmed cell death (PCD) at the late meiotic stage, providing nutrients for further development of microspores, including the formation of the pollen wall. However, the molecular basis of tapetum PCD remains elusive. Here we report a tapetum PCD-related mutant in rice (Oryza sativa), earlier degraded tapetum 1 (edt1), that shows complete pollen abortion associated with earlier-than-programmed tapetum cell death. EDT1 encodes a subunit of ATP-citrate lyase (ACL), and is specifically expressed in the tapetum of anthers. EDT1 localized in both the nucleus and the cytoplasm as observed in rice protoplast transient assays. We demonstrated that the A and B subunits of ACL interacted with each other and might function as a heteromultimer in the cytoplasm. EDT1 catalyzes the critical steps in cytosolic acetyl-CoA synthesis. Our data indicated a decrease in ATP level, energy charge, and fatty acid content in mutant edt1 anthers. In addition, the genes encoding secretory proteases or lipid transporters, and the transcription factors known to regulate PCD, were downregulated. Our results demonstrate that the timing of tapetum PCD must be tightly regulated for successful pollen development, and that EDT1 is involved in the tapetum PCD process. This study furthers our understanding of the molecular basis of pollen fertility and fecundity in rice and may also be relevant to other flowering plants.

Hybrid Sterility in Rice (Oryza sativa L.) Involves the Tetratricopeptide Repeat Domain Containing Protein.

Intersubspecific hybrid sterility is a common form of reproductive isolation in rice (Oryza sativa L.), which significantly hampers the utilization of heterosis between indica and japonica varieties. Here, we elucidated the mechanism of S7, which specially causes Aus-japonica/indica hybrid female sterility, through cytological and genetic analysis, map-based cloning, and transformation experiments. Abnormal positioning of polar nuclei and smaller embryo sac were observed in F1 compared with male and female parents. Female gametes carrying S7(cp) and S7(i) were aborted in S7(ai)/S7(cp) and S7(ai)/S7(i), respectively, whereas they were normal in both N22 and Dular possessing a neutral allele, S7(n) S7 was fine mapped to a 139-kb region in the centromere region on chromosome 7, where the recombination was remarkably suppressed due to aggregation of retrotransposons. Among 16 putative open reading frames (ORFs) localized in the mapping region, ORF3 encoding a tetratricopeptide repeat domain containing protein was highly expressed in the pistil. Transformation experiments demonstrated that ORF3 is the candidate gene: downregulated expression of ORF3 restored spikelet fertility and eliminated absolutely preferential transmission of S7(ai) in heterozygote S7(ai)/S7(cp); sterility occurred in the transformants Cpslo17-S7(ai) Our results may provide implications for overcoming hybrid embryo sac sterility in intersubspecific hybrid rice and utilization of hybrid heterosis for cultivated rice improvement.

The role of OsMSH4 in male and female gamete development in rice meiosis.

Meiosis is essential for gametogenesis in sexual reproduction in rice (Oryza sativa L.). We identified a MutS-homolog (MSH) family gene OsMSH4 in a trisomic plant. Cytological analysis showed that developments of both pollen and embryo sacs in an Osmsh4 mutant were blocked due to defective chromosome pairing. Compared with the wild type, the Osmsh4 mutant displayed a significant ~21.9% reduction in chiasma frequency, which followed a Poisson distribution, suggesting that class I crossover formation in the mutant was impaired. Temporal and spatial expression pattern analyses showed that OsMSH4 was preferentially expressed in meiocytes during their meiosis, indicating a critical role in gametogenesis. Subcellular localization showed that OsMSH4-green fluorescent protein was predominantly located in the nucleus. OsMSH4 could interact with another MSH member (OsMSH5) through the N-terminus and C-terminus, respectively. Direct physical interaction between OsMSH5, OsRPA1a, OsRPA2b, OsRPA1c, and OsRPA2c was identified by yeast two-hybrid assays and further validated by pull-down assays. Our results supported the conclusion that the OsMSH4/5 heterodimer plays a key role in regulation of crossover formation during rice meiosis by interaction with the RPA complex.