Cheng-Jiang Ruan

Halophyte improvement for a salinized world

It is more important to improve the salt tolerance of crops in a salinized world with the situations of increasing populations, declining crop yields, and a decrease in agricultural lands. Attempts to produce salt-tolerant crops have involved the manipulation of existing crops through conventional breeding, genetic engineering and marker-assisted selection (MAS). However, these have, so far, not produced lines growing on highly saline water. Hence, the domestication of wild halophytes as crops appears to be a feasible way to develop agriculture in highly saline environments. In this review, at first, the assessment criteria of salt tolerance for halophytes are discussed. The traditional criteria for the classification of salinity in crops are less applicable to strong halophytes with cubic growth curves at higher salinities. Thus, realistic assessment criteria for halophytes should be evaluated at low and high salinity levels. Moreover, absolute growth rather than relative growth in fields during a crops life cycle should be considered. Secondly, the use of metabolomics to understand the mechanisms by which halophytes respond to salt tolerance is highlighted as is the potential for metabolomics-assisted breeding of this group of plants. Metabolomics provides a better understanding of the changes in cellular metabolism induced by salt stress. Identification of metabolic quantitative trait loci (QTL) associated with salt tolerance might provide a new method to aid the selection of halophyte improvement. Thirdly, the identification of germplasm-regression-combined (GRC) marker-trait association and its potential to identifying markers associated with salt tolerance is outlined. Results of MAS/linkage map-QTL have been modest because of the absence of QTLs with tight linkage, the non-availability of mapping populations and the substantial time needed to develop such populations. To overcome these limitations, identification by GRC-based marker-trait association has been successfully applied to many plant traits, including salt tolerance. Finally, we provide a prospect on the challenges and opportunities for halophyte improvement, especially in the integration of metabolomics- and GRC-marker-assisted selection towards new or unstudied halophyte breeding, for which no other genetic information, such as linkage maps and QTL, are available.

Mucilage and polysaccharides in the halophyte plant species Kosteletzkya virginica: Localization and composition in relation to salt stress

Mucilage is thought to play a role in salinity tolerance in certain halophytic species by regulating water ascent and ion transport. The localization and composition of mucilage in the halophyte Kosteletzkya virginica was therefore investigated. Plants were grown in a hydroponic system in the presence or absence of 100mM NaCl and regularly harvested for growth parameter assessment and mucilage analysis with the gas liquid chromatography method. NaCl treatment stimulated shoot growth and biomass accumulation, had little effect on shoot and root water content, and reduced leaf water potential (Psi(w)), osmotic potential (Psi(s)) as well as stomatal conductance (g(s)). Mucilage increased in shoot, stems and roots in response to salt stress. Furthermore, changes were also observed in neutral monosaccharide components. Levels of rhamnose and uronic acid increased with salinity. Staining with a 0.5% alcian blue solution revealed the presence of mucopolyssacharides in xylem vessels and salt-induced mucilaginous precipitates on the leaf abaxial surface. Determination of ion concentrations showed that a significant increase of Na(+) and a decrease of K(+) and Ca(2+) simultaneously occurred in tissues and in mucilage under salt stress. Considering the high proportion of rhamnose and uronic acid in stem mucilage, we suggest that the pectic polysaccharide could be involved in Na(+) fixation, though only a minor fraction of accumulated sodium appeared to be firmly bound to mucilage.

Metabolomics: Creating new potentials for unraveling the mechanisms in response to salt and drought stress and for the biotechnological improvement of xero-halophytes

Breeders have long been interested in understanding the biological function and mechanism of xero-halophytes and their ability for growth in drought-stricken and salinized environments. However, the mechanisms in response to stress have been difficult to unravel because their defenses require regulatory changes to the activation of multiple genes and pathways. Metabolomics is becoming a key tool in comprehensively understanding the cellular response to abiotic stress and represents an important addition to the tools currently employed in genomics-assisted selection for plant improvement. In this review, we highlight the applications of plant metabolomics in characterizing metabolic responses to salt and drought stress, and identifying metabolic quantitative trait loci (QTLs). We also discuss the potential of metabolomics as a tool to unravel stress response mechanisms, and as a viable option for the biotechnological improvement of xero-halophytes when no other genetic information such as linkage maps and QTLs are available, by combining with germplasm-regression-combined marker-trait association identification.

A critical review on the improvement of photosynthetic carbon assimilation in C3 plants using genetic engineering.

Global warming is one of the most serious challenges facing us today. It may be linked to the increase in atmospheric CO2 and other greenhouse gases (GHGs), leading to a rise in sea level, notable shifts in ecosystems, and in the frequency and intensity of wild fires. There is a strong interest in stabilizing the atmospheric concentration of CO2 and other GHGs by decreasing carbon emission and/or increasing carbon sequestration. Biotic sequestration is an important and effective strategy to mitigate the effects of rising atmospheric CO2 concentrations by increasing carbon sequestration and storage capacity of ecosystems using plant photosynthesis and by decreasing carbon emission using biofuel rather than fossil fuel. Improvement of photosynthetic carbon assimilation, using transgenic engineering, potentially provides a set of available and effective tools for enhancing plant carbon sequestration. In this review, firstly different biological methods of CO2 assimilation in C3, C4 and CAM plants are introduced and three types of C4 pathways which have high photosynthetic performance and have evolved as CO2 pumps are briefly summarized. Then (i) the improvement of photosynthetic carbon assimilation of C3 plants by transgenic engineering using non-C4 genes, and (ii) the overexpression of individual or multiple C4 cycle photosynthetic genes (PEPC, PPDK, PCK, NADP–ME and NADP-MDH) in transgenic C3 plants (e.g. tobacco, potato, rice and Arabidopsis) are highlighted. Some transgenic C3 plants (e.g. tobacco, rice and Arabidopsis) overexpressing the FBP/SBPase, ictB and cytochrome c6 genes showed positive effects on photosynthetic efficiency and growth characteristics. However, over the last 28 years, efforts to overexpress individual, double or multiple C4 enzymes in C3 plants like tobacco, potato, rice, and Arabidopsis have produced mixed results that do not confirm or eliminate the possibility of improving photosynthesis of C3 plants by this approach. Finally, a prospect is provided on the challenges of enhancing carbon assimilation of C3 plants using transgenic engineering in the face of global warming, and the trends of the most promising approaches to improving the photosynthetic performance of C3 plants.

Evolutionary Assurance vs. Mixed Mating

Reproductive assurance is a widely accepted explanation for the evolution of selfing, although theory suggests that an evolutionarily stable mixed mating strategy does not maximize seed production. We present a correlation analysis involving 28 species representing 23 families showing that selfing can evolve independently of inbreeding depression. We discuss the cost-benefit trade-off of selfing, in particular the incongruence of whether delayed selfing provides reproductive assurance in 22 species representing 14 families, in which pollen and seed discounting are minimized when pollinators or mates are scarce. Reproductive assurance, in response to frequent pollinator failure, can be reconciled with an evolutionarily stable mixed mating system contributed to by delayed selfing, which is still advantageous even if there is strong inbreeding depression.

Adaptive Significance of Floral Movement

Since Darwin observed the reconfiguration of pollinia in orchards and referred to it as a function to reduce self-pollination, diverse floral movements have been investigated and various hypotheses have been proposed to explain their adaptive significance. However, adaptive significance of floral movement in some species has yet to be fully explained. Increasing evidence suggests that some floral movements, which have previously been considered as a mechanism to avoid self-pollination, may act as a mechanism to reduce intrafloral male-female interference. In this review, we first explore insect-induced floral movement—such as secondary pollen presentation—that enhances the efficiency and accuracy of pollination. Secondly, we outline the active movements of different floral structures of pistil (style), stamen (filament, anther, pollen), and corolla, such as flexistyly, pollen sliding and catapulting, and anther rotation. Thirdly, we introduce movement herkogamy, which makes herkogamy decrease or increase via the movements of floral structures, especially decreased approach herkogamy via style curvature in the Malvaceae with a monadelphous column. Fourthly, we highlight the different adaptive significances in floral movements for understanding their evolution, including reduction in intrafloral male–female interference, promotion of outcrossing and/or avoidance of self-pollination, delayed autonomous selfing, and tolerance to harsh environments. In particular, we explore the possibility of three functions of one floral movement in one species, which differs from the generally recognized and conventional notion of one floral movement in one species with only one or two functional mechanisms. Finally, we provide perspectives on the challenges and opportunities for using demographic and molecular genetic approaches to (i) study the relative importance and evolutionary mechanism of different adaptive significances in one floral movement; and (ii) simultaneously investigate the floral movement and correlative traits of broader species in related or unrelated families to test how they evolved and the evolutionary relationship between their functions.

Adaptive evolution of context-dependent style curvature in some species of the Malvaceae: a molecular phylogenetic approach

The evolution of floral movement responding to pollination environments has long intrigued biologists. This has been mostly demonstrated in different species, but has as yet few explanations at the family level. Style curvature occurs in 23 species of eight genera among our observed and surveyed 52 species of 13 genera in the Malvaceae. To analyze the origin of style curvature in these species, we mapped this and correlated characters onto molecular phylogenetic trees that were constructed using the combination of the chloroplast DNA sequences of ndhF and the rpl16 intron. The results showed that style curvature evolved at least five times in species with herkogamous flowers. The occurrence of style curvature was associated with a shift to annual or perennial herbs with herkogamous flowers, which have similar ecological distributions with unpredictable pollinator environments. Style curvature appears to have evolved to facilitate delayed selfing if outcrossing fails under unpredictable pollination conditions.

Analysis of genetic relationships in sea buckthorn (Hippophae rhamnoides) germplasm from China and other countries using ISSR markers

SUMMARY Sea buckthorn (Hippophae rhamnoides) is an ecologically and economically important shrub or small tree widely distributed in China, Russia, and Mongolia and its berries are rich in bio-active compounds. Inter-simple sequence repeat (ISSR) markers were used to assess genetic relationships among 78 cultivars and lines of H. rhamnoides ssp. mongolica and hybrids between ssp. mongolica and ssp. sinensis. Thirteen ISSR primers generated 143 bands, 139 (97.2%) of which were polymorphic, with the number of polymorphic bands per primer ranging from 8–17. A low coefficient of gene differentiation (0.0588) indicated that genetic diversity existed mainly within populations. Pairwise genetic similarities among the 78 cultivars and lines ranged from 0.362–0.939. Cluster analysis indicated that these 78 cultivars and lines could be classified into two groups, in good agreement with their taxonomic classification. Euclidean distances and multi-dimensional scaling confirmed the spatial positions of cultivars and lines of H. rhamnoides ssp. mongolica and its hybrids. We found that line HS22 (of unknown parentage) and cultivar ‘CY’, with a large fruit trait, had close parental relationships, and that lines TF2–13 and XE2 which shared the same pedigree had a high oil content in their dry pulp. Our data provide a reliable and simple method to identify genetic relationships among cultivars and lines with desirable traits for sea buckthorn breeding programmes.

Assessment of genetic stability of propagated plantlets of four sea buckthorn (Hippophae) cultivars and the establishment of genetic relationships between them by ISSR markers.

The common sea buckthorn or seaberry (Hippophae rhamnoides) is important environmentally, commercially, and as a new berry crop. Some morphological differences among mother plants and lines obtained by cuttings often lead a purchaser to question if the propagated plantlets are true-to-name cultivars. Intersimple sequence repeat (ISSR) markers were employed to assess the genetic stability of lines obtained by cuttings of four H. rhamnoides cultivars and the genetic relationships among them. Fifteen ISSR primers generated 174 bands among the 35 samples of four cultivars, 158 of which (90.8%) were polymorphic. Percentages of polymorphic and unique bands between mother plant and propagated plantlets ranged from 53.21% to 77.17% and from 7.09% to 13.76%, respectively. Cluster analysis based on ISSR data indicated that at a Jaccard coefficient of 0.78, mother plant and lines obtained by cuttings for each cultivar were grouped into different subclusters, respectively, which could be further clustered into different sub-subclusters. Our data first indicated that the genotype was affected by the cutting process to a certain degree, because there were some morphological and low molecular variations between the mother plant and lines obtained by cuttings. Information generated from this study can be used to select parents for hybrid development to maximize desirable agronomic traits in a breeding program aimed at developing segregating populations to map genes controlling special traits in H. rhamnoides.

High-crown grafting to increase low yields in Camellia oleifera

ABSTRACT Tea oil camellia (Camellia oleifera) is a perennial evergreen shrub or small tree with multiple uses. Its seed oil contains rich bioactive compounds with powerful nutritional and medicinal values. To improve low seed yield in natural forests of this species, the new grafting technique of high-grafting and change-crown is being widely used. This usually has three grafting methods, inlay graft by separating bark (IGSB), bark xylem graft by cutting stock (BXGCS), and cleft graft (CG). In this research, we (1) investigated growth, development, fruit yield, and traits of trees after high-grafting and (2) tested effects of grafting methods (IGSB, BXGCS, and CG) and times (spring, summer, and autumn) on survival rates. Results indicated that sprouted scions flowered and set fruit in the third year after high-grafting, and grafted trees produced higher oil yields in the fourth year. Both grafting methods and times significantly influence grafting survival rates. The optimal grafting method for this species is BXGCS, resulting in a 77.4% survival rate in the summer. These results not only demonstrate that this new grafting technique is advantageous to improve low-yield trees, but also that grafting method and time affected survival rate, contributing to enhanced productivity.