Quantitative genetic analysis of embryo heterosis in faba bean (Vicia faba L.)

Generation Mean Analysis, Heterosis, and Genetic Diversity in Five Egyptian Faba Beans and Their Hybrids

The faba bean (Vicia faba L.) is a major legume crop; thus, it is important to apply various biometrical techniques to develop the most efficient breeding procedures to face biotic and abiotic stressors. During the four consecutive winter seasons of 2017–2021, five populations of five faba bean hybrids were studied at Sakha agricultural research station in Egypt. Five basic generations, including two parents (P1 and P2) and the first, second, and third generations, were studied. This analysis found significant variations between generations in all attributes studied in all crosses (P1, P2, F1, F2, and F3). Sakha 4 was the earliest parent (138 days) based on the maturity date, whereas Giza 40 had the most significant number of pods and seeds per plant (25.68–78.94), and Giza 716 had the tallest plant height (124.00 cm). Giza 843 and Sakha 4 had the highest seed yield per plant values (62.84 g and 61.77 g). The data demonstrated highly substantial heterosis in the favorable direction over mid and better parents for all features, except for the number of branches in Cross 3 (Giza 40 × Giza 843) over mid and better parents and a maturity date in Cross 1 over mid parents. Contrarily, opposite-direction dominance and dominance × dominance effects increased narrow-sense heredity. Broad-sense heritability values for all examined characteristics were high in all crosses, ranging from 90.24% to 97.67%. In both Crosses 5 (Giza 716 × Qahera 4) and 3, genetic advance through selection ranged from 1.73% at the maturity date to 95.12% for seed yield per plant. Cross 3 (Giza 40 × Giza 843) had the greatest number of branches, pods, and seeds per plant. In conclusion, this study advances our understanding of employing faba beans in breeding programs.

Seed Development and Protein Accumulation Patterns in Faba Bean (Vicia faba, L.)

A major objective in faba bean breeding is to improve its protein quality by selecting cultivars with enhanced desirable physicochemical properties. However, the protein composition of the mature seed is determined by a series of biological processes occurring during seed growth. Thus, any attempt to explain the final seed composition must consider the dynamics of the seed proteome during seed development. Here, we investigated the proteomic profile of developing faba bean seeds across 12 growth stages from 20 days after pollination (DAP) to full maturity. We analyzed trypsin-digested total protein extracts from the seeds at different growth stages by liquid chromatography-tandem mass spectrometry (LC-MS/MS), identifying 1217 proteins. The functional clusters of these proteins showed that, in early growth stages, proteins related to cell growth, division, and metabolism were most abundant compared to seed storage proteins that began to accumulate from 45 DAP. Moreover, label-free quantification of the relative abundance of seed proteins, including important globulin proteins, revealed several distinct temporal accumulation trends among the protein classes. These results suggest that these proteins are regulated differently and require further understanding of the impact of the different environmental stresses occurring at different grain filling stages on the expression and accumulation of these seed storage proteins.

Conventional and Molecular Breeding Tools for Accelerating Genetic Gain in Faba Bean (Vicia Faba L.)

Faba bean is a cool-season grain legume crop, which is grown worldwide for food and feed. Despite a decrease in area under faba bean in the past, the interest in growing faba bean is increasing globally due to its high seed protein content and its excellent ecological service. The crop is, however, exposed to diverse biotic and abiotic stresses causing unstable, low grain yield. Although, sources of resistance to main diseases, such as ascochyta blight (Ascochyta fabae Speg.), rust (Uromyces viciae-fabae (Pers.) Schroet.), chocolate spot (Botrytis fabae Sard.) and gall disease (Physioderma viciae), have been identified, their resistance is only partial and cannot prevent grain yield losses without agronomical practices. Tightly associated DNA markers for host plant resistance genes are needed to enhance the level of resistance. Less progress has been made for abiotic stresses. Different breeding methods are proposed, but until now line breeding, based on the pedigree method, is the dominant practice in breeding programs. Nonetheless, the low seed multiplication coefficient and the requirement for growing under insect-proof enclosures to avoid outcrossing hampers breeding, along with the lack of tools such as double haploid system and cytoplasmic male sterility. This reduces breeding population size and speed of breeding hence the chances of capturing rare combinations of favorable alleles. Availability and use of the DNA markers such as vicine-convicine (vc -) and herbicide tolerance in breeding programs have encouraged breeders and given confidence in marker assisted selection. Closely linked QTL for several biotic and abiotic stress tolerance are available and their verification and conversion in breeder friendly platform will enhance the selection process. Recently, genomic selection and speed breeding techniques together with genomics have come within reach to accelerate the genetic gains in faba bean. Advancements in genomic resources with other breeding tools, methods and platforms will enable to accelerate the breeding process for enhancing genetic gain in this species.

Early changes of gene activity in developing seedlings of Arabidopsis hybrids relative to parents may contribute to hybrid vigour

Hybrid vigour (heterosis) has been used for decades in crop industries, especially in the production of maize and rice. Hybrid varieties usually exceed their parents in plant biomass and seed yield. But the molecular basis of hybrid vigour is not fully understood. In this project, we studied heterosis at early stages of seedling development in Arabidopsis hybrids derived from crossing Ler and C24 accessions. We found that early heterosis is associated with non-additive gene expression that resulted from earlier changes in gene expression in the hybrids relative to the parents. The non-additively expressed genes are involved in metabolic pathways, including photosynthesis, critical for plant growth. The early increased expression levels of genes involved in energy production in hybrids is associated with heterosis in the young seedlings that could be essential for biomass heterosis at later developmental stages of the plant.

Intraspecific Arabidopsis hybrids show different patterns of heterosis despite the close relatedness of the parental genomes

Heterosis is important for agriculture; however, little is known about the mechanisms driving hybrid vigor. Ultimately, heterosis depends on the interactions of specific alleles and epialleles provided by the parents, which is why hybrids can exhibit different levels of heterosis, even within the same species. We characterize the development of several intraspecific Arabidopsis (Arabidopsis thaliana) F1 hybrids that show different levels of heterosis at maturity. We identify several phases of heterosis beginning during embryogenesis and culminating in a final phase of vegetative maturity and seed production. During each phase, the hybrids show different levels and patterns of growth, despite the close relatedness of the parents. For instance, during the vegetative phases, the hybrids develop larger leaves than the parents to varied extents, and they do so by exploiting increases in cell size and cell numbers in different ratios. Consistent with this finding, we observed changes in the expression of genes known to regulate leaf size in developing rosettes of the hybrids, with the patterns of altered expression differing between combinations. The data show that heterosis is dependent on changes in development throughout the growth cycle of the hybrid, with the traits of mature vegetative biomass and reproductive yield as cumulative outcomes of heterosis at different levels, tissues, and times of development.

Heterosis manifestation during early Arabidopsis seedling development is characterized by intermediate gene expression and enhanced metabolic activity in the hybrids

Heterosis-associated cellular and molecular processes were analyzed in seeds and seedlings of Arabidopsis thaliana accessions Col-0 and C24 and their heterotic hybrids. Microscopic examination revealed no advantages in terms of hybrid mature embryo organ sizes or cell numbers. Increased cotyledon sizes were detectable 4 days after sowing. Growth heterosis results from elevated cell sizes and numbers, and is well established at 10 days after sowing. The relative growth rates of hybrid seedlings were most enhanced between 3 and 4 days after sowing. Global metabolite profiling and targeted fatty acid analysis revealed maternal inheritance patterns for a large proportion of metabolites in the very early stages. During developmental progression, the distribution shifts to dominant, intermediate and heterotic patterns, with most changes occurring between 4 and 6 days after sowing. The highest incidence of heterotic patterns coincides with establishment of size differences at 4 days after sowing. In contrast, overall transcript patterns at 4, 6 and 10 days after sowing are characterized by intermediate to dominant patterns, with parental transcript levels showing the largest differences. Overall, the results suggest that, during early developmental stages, intermediate gene expression and higher metabolic activity in the hybrids compared to the parents lead to better resource efficiency, and therefore enhanced performance in the hybrids.

Hybrid embryos of Vicia faba develop enhanced sink strength, which is established during early development

Selfed and crossed seeds of two homozygous Vicia faba lines served as models for the analysis of the physiological and molecular mechanisms underlying embryo heterosis. Profiles of transcripts, metabolites and seed contents of developing embryos were analysed to compare the means of reciprocally crossed and selfed seeds growing on the same mother plants. The mean weight of mature hybrid seeds was demonstrably higher, revealing mid-parent heterosis. Hybrid embryos exhibited a prolonged early phase of development and delayed onset of storage activity. Accordingly, transcript profiling indicates stimulation of cell proliferation, an effect, which is potentially mediated by activation of auxin functions within a framework of growth-related transcription factors. At the transcript level, activated cell proliferation increased assimilate uptake activity and thereby seed sink strength. This situation might finally lead to the increased size of the hybrid seeds. We conclude that hybrid seeds are characterised by accelerated growth during early development, which increases storage capacity and leads to higher metabolic fluxes. These needs are, at least partially, met by increased assimilate uptake capacity. The stimulated growth of hybrid seeds shifted metabolite profiles and potentially depleted available pools. Such metabolic shifts are most likely secondary effects resulting from the higher storage capacity of hybrid seeds, a heterotic feature, which is itself established very early in seed development.

Dynamics of maternal and paternal effects on embryo and seed development in wild radish (Raphanus sativus)

BACKGROUND AND AIMS

Variability in embryo development can influence the rate of seed maturation and seed size, which may have an impact on offspring fitness. While it is expected that embryo development will be under maternal control, more controversial hypotheses suggest that the pollen donor and the embryo itself may influence development. These latter possibilities are, however, poorly studied. Characteristics of 10-d-old embryos and seeds of wild radish (Raphanus sativus) were examined to address: (a) the effects of maternal plant and pollen donor on development; (b) the effects of earlier reproductive events (pollen tube growth and fertilization) on embryos and seeds, and the influence of embryo size on mature seed mass; (c) the effect of water stress on embryos and seeds; (d) the effect of stress on correlations of embryo and seed characteristics with earlier and later reproductive events and stages; and (e) changes in maternal and paternal effects on embryo and seed characteristics during development.

METHODS

Eight maternal plants (two each from four families) and four pollen donors were crossed and developing gynoecia were collected at 10 d post-pollination. Half of the maternal plants experienced water stress. Characteristics of embryos and seeds were summarized and also compared with earlier and later developmental stages.

KEY RESULTS

In addition to the expected effects of the maternal plants, all embryo characters differed among pollen donors. Paternal effects varied over time, suggesting that there are windows of opportunity for pollen donors to influence embryo development. Water-stress treatment altered embryo characteristics; embryos were smaller and less developed. In addition, correlations of embryo characteristics with earlier and later stages changed dramatically with water stress.

CONCLUSIONS

The expected maternal effects on embryo development were observed, but there was also evidence for an early paternal role. The relative effects of these controls may change over time. Thus, there may be times in development when selection on the maternal, paternal or embryo contributions to development are more and less likely.