Genome-scale analysis and comparison of gene expression profiles in developing and germinated pollen in Oryza sativa

<p>Abstract</p> <p>Background</p> <p>Pollen development from the microspore involves a series of coordinated cellular events, and the resulting mature pollen has a specialized function to quickly germinate, produce a polar-growth pollen tube derived from the vegetative cell, and deliver two sperm cells into the embryo sac for double fertilization. The gene expression profiles of developing and germinated pollen have been characterised by use of the eudicot model plant <it>Arabidopsis</it>. Rice, one of the most important cereal crops, has been used as an excellent monocot model. A comprehensive analysis of transcriptome profiles of developing and germinated pollen in rice is important to understand the conserved and diverse mechanism underlying pollen development and germination in eudicots and monocots.</p> <p>Results</p> <p>We used Affymetrix GeneChip^®Rice Genome Array to comprehensively analyzed the dynamic changes in the transcriptomes of rice pollen at five sequential developmental stages from microspores to germinated pollen. Among the 51,279 transcripts on the array, we found 25,062 pollen-preferential transcripts, among which 2,203 were development stage-enriched. The diversity of transcripts decreased greatly from microspores to mature and germinated pollen, whereas the number of stage-enriched transcripts displayed a "U-type" change, with the lowest at the bicellular pollen stage; and a transition of overrepresented stage-enriched transcript groups associated with different functional categories, which indicates a shift in gene expression program at the bicellular pollen stage. About 54% of the now-annotated rice F-box protein genes were expressed preferentially in pollen. The transcriptome profile of germinated pollen was significantly and positively correlated with that of mature pollen. Analysis of expression profiles and coexpressed features of the pollen-preferential transcripts related to cell cycle, transcription, the ubiquitin/26S proteasome system, phytohormone signalling, the kinase system and defense/stress response revealed five expression patterns, which are compatible with changes in major cellular events during pollen development and germination. A comparison of pollen transcriptomes between rice and <it>Arabidopsis </it>revealed that 56.6% of the rice pollen preferential genes had homologs in <it>Arabidopsis </it>genome, but 63.4% of these homologs were expressed, with a small proportion being expressed preferentially, in <it>Arabidopsis </it>pollen. Rice and <it>Arabidopsis </it>pollen had non-conservative transcription factors each.</p> <p>Conclusions</p> <p>Our results demonstrated that rice pollen expressed a set of reduced but specific transcripts in comparison with vegetative tissues, and the number of stage-enriched transcripts displayed a "U-type" change during pollen development, with the lowest at the bicellular pollen stage. These features are conserved in rice and <it>Arabidopsis</it>. The shift in gene expression program at the bicellular pollen stage may be important to the transition from earlier cell division to later pollen maturity. Pollen at maturity pre-synthesized transcripts needed for germination and early pollen tube growth. The transcription regulation associated with pollen development would have divergence between the two species. Our results also provide novel insights into the molecular program and key components of the regulatory network regulating pollen development and germination.</p

Mechanical performance of 22SiMn2TiB steel welded with low-transformation-temperature filler wire and stainless steel filler wire

TX-80 low-transformation-temperature (LTT) welding wire was used to replace the traditional ER 307Si welding wire to realize the connection of 22SiMn2TiB armor steel in manual overlay welding. The previously existing issues, such as welding cracks, large welding deformation, and severe welding residual stress, were solved to ensure good strength and ductility requirements. In particular, with the same welding conditions, TX-80 LTT wire eliminates welding cracks. It reduces the welding deformation no matter the base pretreatment of pre-setting angle or no pre-setting angle. By comparison, it was found that the microstructure at the TX-80 weld is mainly composed of martensite and a small amount of retained austenite. In contrast, the microstructure of the ER 307Si weld consists of a large amount of austenite and a small amount of skeleton-like ferrite. The variation trend of residual stress and microhardness from the weld to the base were investigated and compared with the mechanical properties of base materials. The TX-80 and the ER 307Si tensile samples elongation is 6.76% and 6.01%, while the ultimate tensile strengths are 877 and 667 MPa, respectively. The average impact toughness at room temperature of the ER 307Si weld is 143.9 J/cm2, much higher than that of the TX-80 weld, which is only 36.7 J/cm2. The relationship between impact and tensile properties with microstructure species and distribution was established. In addition, the fracture surface of the tensile and the impact samples was observed and analyzed. Deeper dimples, fewer pores, larger radiation zone, and shear lips of TX-80 samples indicate better tensile ductility and worse impact toughness than those of ER 307Si weld.</p

Phylogeny of Leontopodium (Asteraceae) in China—with a reference to plastid genome and nuclear ribosomal DNA

The infrageneric taxonomy system, species delimitation, and interspecies systematic relationships of Leontopodium remain controversial and complex. However, only a few studies have focused on the molecular phylogeny of this genus. In this study, the characteristics of 43 chloroplast genomes of Leontopodium and its closely related genera were analyzed. Phylogenetic relationships were inferred based on chloroplast genomes and nuclear ribosomal DNA (nrDNA). Finally, together with the morphological characteristics, the relationships within Leontopodium were identified and discussed. The results showed that the chloroplast genomes of Filago, Gamochaeta, and Leontopodium were well-conserved in terms of gene number, gene order, and GC content. The most remarkable differences among the three genera were the length of the complete chloroplast genome, large single-copy region, small single-copy region, and inverted repeat region. In addition, the chloroplast genome structure of Leontopodium exhibited high consistency and was obviously different from that of Filago and Gamochaeta in some regions, such as matk, trnK (UUU)-rps16, petN-psbM, and trnE (UUC)-rpoB. All the phylogenetic trees indicated that Leontopodium was monophyletic. Except for the subgeneric level, our molecular phylogenetic results were inconsistent with the previous taxonomic system, which was based on morphological characteristics. Nevertheless, we found that the characteristics of the leaf base, stem types, and carpopodium base were phylogenetically correlated and may have potential value in the taxonomic study of Leontopodium. In the phylogenetic trees inferred using complete chloroplast genomes, the subgen. Leontopodium was divided into two clades (Clades 1 and 2), with most species in Clade 1 having herbaceous stems, amplexicaul, or sheathed leaves, and constricted carpopodium; most species in Clade 2 had woody stems, not amplexicaul and sheathed leaves, and not constricted carpopodium