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The wood sorrel family, Oxalidaceae, is mainly composed of annual or perennial herbs, a few shrubs, and trees distributed from temperate to tropical zones. Members of Oxalidaceae are of high medicinal, ornamental, and economic value. Despite the rich diversity and value of Oxalidaceae, few molecular markers or plastomes are available for phylogenetic analysis of the family. Here, we reported four new whole plastomes of Oxalidaceae and compared them with plastomes of three species in the family, as well as the plastome of Rourea microphylla in the closely related family Connaraceae. The eight plastomes ranged in length from 150,673 bp (Biophytum sensitivum) to 156,609 bp (R. microphylla). Genome annotations revealed a total of 129–131 genes, including 83–84 protein-coding genes, eight rRNA genes, 37 tRNA genes, and two to three pseudogenes. Comparative analyses showed that the plastomes of these species have minor variations at the gene level. The smaller plastomes of herbs B. sensitivum and three Oxalis species are associated with variations in IR region sizes, intergenic region variation, and gene or intron loss. We identified sequences with high variation that may serve as molecular markers in taxonomic studies of Oxalidaceae. The phylogenetic trees of selected superrosid representatives based on 76 protein-coding genes corroborated the Oxalidaceae position in Oxalidales and supported it as a sister to Connaraceae. Our research also supported the monophyly of the COM (Celastrales, Oxalidales, and Malpighiales) clade., Highlights • Plastomes from the genus Biophytum (Oxalidaceae) and the family Connaraceae are reported for the first time. • Little plastome variation was observed among genera of Oxalidaceae. • Several divergence hotspot regions were identified in the Oxalidaceae species. • The systematic position of Oxalidaceae was confirmed as sister to Connaraceae within Oxalidales.

A new orchid species, Cymbidium brevifolium, from Hubei Province, China, is described and illustrated based on morphological and molecular analyses. A detailed comparison between the newly discovered orchid and other members of Cymbidium was conducted. The new orchid is distinct from all other recognized species in Cymbidium. Phylogenetic analyses based on nuclear (ITS) and plastid DNA (matK and rbcL) sequence data support the status of C. brevifolium as a new species, which is sister to C. faberi.

Background Members of the plant-specific YABBY gene family are thought to play an important role in the development of leaf, flower, and fruit. The YABBY genes have been characterized and regarded as vital contributors to fruit development in Arabidopsis thaliana and tomato, in contrast to that in the important tropical economic fruit star fruit (Averrhoa carambola), even though its genome is available. Methods In the present study, a total of eight YABBY family genes (named from AcYABBY1 to AcYABBY8) were identified from the genome of star fruit, and their phylogenetic relationships, functional domains and motif compositions, physicochemical properties, chromosome locations, gene structures, protomer elements, collinear analysis, selective pressure, and expression profiles were further analyzed. Results Eight AcYABBY genes (AcYABBYs) were clustered into five clades and were distributed on five chromosomes, and all of them had undergone negative selection. Tandem and fragment duplications rather than WGD contributed to YABBY gene number in the star fruit. Expression profiles of AcYABBYs from different organs and developmental stages of fleshy fruit indicated that AcYABBY4 may play a specific role in regulating fruit size. These results emphasize the need for further studies on the functions of AcYABBYs in fruit development.

Oxalidaceae is one of the most important plant families in horticulture, and its key commercially relevant genus, Averrhoa, has diverse growth habits and fruit types. Here, we describe the assembly of a high-quality chromosome-scale genome sequence for Averrhoa carambola (star fruit). Ks distribution analysis showed that A. carambola underwent a whole-genome triplication event, i.e., the gamma event shared by most eudicots. Comparisons between A. carambola and other angiosperms also permitted the generation of Oxalidaceae gene annotations. We identified unique gene families and analyzed gene family expansion and contraction. This analysis revealed significant changes in MADS-box gene family content, which might be related to the cauliflory of A. carambola. In addition, we identified and analyzed a total of 204 nucleotide-binding site, leucine-rich repeat receptor (NLR) genes and 58 WRKY genes in the genome, which may be related to the defense response. Our results provide insights into the origin, evolution and diversification of star fruit.

The use of high-grade, low alloy abrasion resistant steels has been limited due to the effects of their high hardness on their formability, machinability, and weldability. In order to increase the wear resistance of the steel without increasing hardness, a new low alloy wear resistant steel reinforced with (Ti,Mo)C particles was developed. The three-body abrasive wear behaviour of the experimental steel has been studied using a standard dry sand rubber wheel wear testing procedure under applied loads of 45 N and 130 N. Experimental observations revealed that nano- and microparticles are uniformly distributed in the martensitic matrix. The analysis of worn surfaces including longitudinal sections of the surfaces showed that the particles can effectively resist micro-cutting, due to which, the main wear mechanism of the experimental steel was through formation of pits and other indications of surface fatigues. Typically, the abrasion resistance of the experimental steel reinforced with particles was, respectively, 1.6 and 1.8 times that of a traditional low alloy wear resistant steel under applied loads of 130 N and 45 N.

Floral color polymorphism can provide great insight into species evolution from a genetic and ecological standpoint. Color variations between species are often mediated by pollinators and are fixed characteristics, indicating their relevance to adaptive evolution, especially between plants within a single population or between similar species. The orchid genus Pleione has a wide variety of flower colors, from violet, rose-purple, pink, to white, but their color formation and its evolutionary mechanism are unclear. Here, we selected the P. limprichtii population in Huanglong, Sichuan Province, China, which displayed three color variations: Rose-purple, pink, and white, providing ideal material for exploring color variations with regard to species evolution. We investigated the distribution pattern of the different color morphs. The ratio of rose-purple:pink:white-flowered individuals was close to 6:3:1. We inferred that the distribution pattern may serve as a reproductive strategy to maintain the population size. Metabolome analysis was used to reveal that cyanindin derivatives and delphidin are the main color pigments involved. RNA sequencing was used to characterize anthocyanin biosynthetic pathway-related genes and reveal different color formation pathways and transcription factors in order to identify differentially-expressed genes and explore their relationship with color formation. In addition, qRT-PCR was used to validate the expression patterns of some of the genes. The results show that PlFLS serves as a crucial gene that contributes to white color formation and that PlANS and PlUFGT are related to the accumulation of anthocyanin which is responsible for color intensity, especially in pigmented flowers. Phylogenetic and co-expression analyses also identified a R2R3-MYB gene PlMYB10, which is predicted to combine with PlbHLH20 or PlbHLH26 along with PlWD40-1 to form an MBW protein complex (MYB, bHLH, and WDR) that regulates PlFLS expression and may serve as a repressor of anthocyanin accumulation-controlled color variations. Our results not only explain the molecular mechanism of color variation in P. limprichtii, but also contribute to the exploration of a flower color evolutionary model in Pleione, as well as other flowering plants.

The study of metal-ceramic sliding wear is important as it occurs in many industrial mechanical systems. The friction behaviour and self-lubricating mechanism of low alloy martensitic steel during reciprocating sliding wear against the WC ceramic ball under an ambient atmosphere and at room temperature were investigated. The reciprocating sliding wear process was characterised using a commercial friction and wear testing machine and a scanning electron microscope. The results showed that there was a self-lubricating phenomenon during reciprocating sliding wear between the experimental steel and the tungsten carbide ceramic ball, and the friction coefficient decreased to 0.3 from 0.53. This is attributed to the high hardness of the subsurface, the lubricating effect of the surface oxide film, and the removal mechanism of layer-by-layer peeling. The evolution of the friction coefficient corresponded to the change in the wear mechanism. During the initial stage of sliding wear, adhesive wear was the primary wear mechanism, while fatigue spalling occurred during steady-state wear. In addition, during the self-lubricating process, the wear growth rate of the experimental steel decreased correspondingly, and the wear surface roughness also showed a decreasing trend.

Low alloy wear-resistant martensitic steels are increasingly prevalent in moderate-to-high temperature applications in machinery. In this study, the reciprocating sliding wear behavior of a designed low alloy martensitic steel (herein called HTP) against silicon nitride has been investigated within the temperature range of 300–500 °C and compared to similar results for another wear-resistant steel (NM400). A commercial high temperature friction and wear tester was used. The evolution of the microstructure and properties of HTP and their influence on the wear process was investigated as a function of temperature. Results have shown that as the tempering temperature was increased to 500 °C, the wear depth was significantly reduced. This is attributed to increasing the strength and hardness by 25%. As a result, high temperature wear resistance of the HTP was increased by a factor of 1.7 times relative to alloy NM400. By delaying the decrease of dislocation density and carbide precipitation during the tempering of the martensite, the transformation of microstructure from tempered martensite to tempered sorbite could be hindered, thereby improving the thermal strength of the HTP alloy's matrix. The material removal mechanisms was observed to change from fatigue spalling and abrasive wear to oxidative wear and plastic deformation when the temperature was increased from 300 °C to 500 °C.

Low alloy abrasion resistant steel is an indispensable material used in the machinery manufacturing industry. In order to further improve its wear performance without increasing its hardness, a series of low alloy wear resistant steel reinforced with TiC particles was developed. The microstructures were characterized by SEM and TEM. The three-body abrasive wear behaviour of experimental steels has been studied using dry sand rubber wheel testing machine under different applied loads, abrasive particles, and rubber wheel rotation speeds. The results showed that the microstructure of the TiC-reinforced low alloy abrasion-resistant steel consisted of a martensite matrix and nano- and micro-sized TiC particles. Although the TiC particles consumed the C element in the matrix, thus reducing the hardness and strength of the experimental steels, the wear resistance did not decrease. The wear resistance of TiC-particle-reinforced steels was proportional to the density of the TiC particles. Furthermore, the worn surface morphology indicated that the abrasive wear mechanism of TiC-reinforced experimental steels was mainly plastic deformation, fracture, and fatigue, which is different from the micro-cutting observed in traditional low alloy abrasion-resistant steel. The different wear mechanism will aid in improving the wear performance of the steels.