Intraspecific heterogeneity of the Vicia faba mitochondrial genome: evidence for multiregional rearrangements in the mitochondrial chromosome associated with coxII-orf192 chimeric gene formation

Summary Previous RFLP-analysis of mtDNA isolated from different lines and cultivars of Vicia faba with respect to variability of the coxII gene revealed two types of mitochondrial genome: one with a normal coxII gene and the other with both normal coxII and chimeric coxII-orf192 genes. In this study we analyzed other regions of these two types of mitochondrial genome and found significant differences in the arrangement of regions around the coxII, coxIII, cob, rrn26 and atpA genes. More detailed analysis of the rrn26 and atpA gene regions showed that these genes are associated with recombinationally active repeats. Restriction maps of the rrn26 and atpA gene regions in different recombinative variants are presented.     

Structural variations in Vicia faba mitochondrial genome

Summary A comparative analysis of the presence of minicircular DNA CCCIB in 16 different lines and cultivars of fertile Vicia faba L. plants was conducted. It was found that copy number of CCCIB ranged from several copies per mitochondrial genome to — probably — zero, depending on cultivar or line. Fertility of plants in these cases was not altered. We chose 10 cultivars and lines among 16 analysed. Mitochondria of five cultivars and lines contained about two CCCIB molecules per one CCCIA. The sixth cultivar contained CCCIB at copy number several times lower. In the last four cultivars CCCIB could not be identified. Copy number analysis of CCC2 in ten chosen cultivars and lines revealed that in eight cases the quantitiy of CCC2 was equal to CCCIA. However, two other cultivars contained about two times lower quantity of CCC2. Parallel to that we observed an increase in quantity of one sequence homologous to CCC2, which in the first eight cultivars and lines could be found only in minor quantities. Comparative restriction analysis revealed notable rearrangement events in mitochondrial DNAs of ten cultivars and lines being investigated. We did not find any correlations between patterns of restriction fragments and copy number of CCCIB. In some cases, rearrangements in Vicia faba mitochondrial genomes caused a duplication of sequences homologous to the Zea mays coxII gene.     

The legumin gene family: structure and evolutionary implications of Vicia faba B-type genes and pseudogenes

We have characterized several Vicia faba genes encoding methionine residue-free group B subunits of the 11S or legumin storage proteins. The respective gene subfamily consists of 10 to 15 members, six of them having been studied by DNA sequence analysis. Four functional genes (LeB2, LeB4, LeB6, LeB7) are highly homologous in their coding region and 0.3 kb of their 3 flanking sequences. On the other hand, two pseudogenes (LeB1, LeB5) have accumulated a large number of mutations including an identical 0.7 kb internal deletion; they are both flanked by a repetitive element. Analysis of sequence changes show that transitions are nearly double as frequent as transversions. CpG is the most infrequent dinucleotide whereas TpA is significantly underrepresented in exon sequences. End points of deletions are correlated with short direct repeats and preferentially found in the two introns. Our studies indicate that the Vicia faba legumin B gene subfamily contains a group of expressed, highly homologous genes as well as more diverged pseudogenes.     

Genetic changes under domestication in Vicia faba

Summary The components of variation within each one of two sets of landraces and/or cultivars of Vicia faba, respectively constituted of primitive and advanced morphological types, were studied by means of two sets of 8 × 8 diallel crosses with two repetitions. The results show that primitive and modern forms differ from each other in both the intensity and the kind of selective pressures acting on them, mainly on those characters more modified through the domestication process: i.e., seed morphology and the number of flowers per node. Because of the paramount importance of the additive component in the primitive forms, it is suggested that the most important type of selection on them is the stabilizing one. On the contrary, in the most advanced forms the selection is directional and disruptive : directional towards greater yields, and disruptive separating two morphological types, major and equina. The plant response to these different selective pressures has been to modify the genetic control of different characters: thus the primitive forms generally show only additivity while the most advanced forms show additivity as well as directional and asymmetrical dominance.     

Sequence analysis of Vicia faba highly repeated DNA: the BamHI repeated sequence families

Cleavage of Vicia faba nuclear DNA with the restriction endonuclease BamHI yielded discrete size classes of 250, 850, 900, 990, 1 150, 1 500 and 1 750 bp of highly repetitive DNA. Each of these sequence families comprised about 3% of the total genomic DNA. Some sequence members from each sequence family were cloned in pBR322 and their primary structures determined. Computer analyses of nucleotide sequences suggested the existence of about 60 bp sequence periodicity within the repeating unit of the 990 bp sequence family, though the extent of homology among the surmised shorter subrepeat units was very low. With other BamHI sequence families, however, the data did not show any clear internal sequence periodicity. The repeat units of the 850 bp and 1 750 bp sequence families contained nucleotide sequences homologous to the 250 bp family sequence. No sequence relationship between or among other sequence families was observed. There was 13–25% sequence variation among 6 cloned members of the 250 bp family and probably also among those of other BamHI repeat families. DNA sequences homologous to these V. faba BamHI repeat families were detected in Pisum sativum DNA by Southern blot hybridization. Furthermore, very weak cross-hybridization was observed with plant DNAs from Phaseolus vulgaris, Triticum aestivum, Cucumis sativus and Trillium kamtschaticum.     

Variability and inheritance of histone genes H3 and H4 in Vicia faba

Summary We have compared copy numbers and blothybridization patterns of histone genes (H3 plus H4) between and within individuals of broad bean (Vicia faba). Copy number differences among individuals in the population of 200 individuals were as great as 27 fold, and as much as 3.2 fold among separate leaves of the same plant. Among F₂ progeny from genetic crosses, up to a 5.4-fold range was seen (mean=3.5 fold), and among F₁ progeny of self-pollinated plants, up to a 5.9-fold range was observed (mean=2.3 fold). Histone gene blot-hybridization patterns for EcoRI and HindIII were also variable among individuals and indicated that the genes are probably clustered in only a few chromosomal loci. The degree of variation in histone gene copy number per haploid genome (2–55 copies, or 27 fold) was similar to that found previously for ribosomal RNA genes (230–22000, or 95 fold) of V. faba. However, the two gene families change independently, since individuals with a high or low copy number for one gene can have either a high or low copy number for the other. The mechanisms(s) for rapid gene copy number change may be similar for these gene families.     

Agrobacterium-mediated transformation of Vicia faba

Among the major grain legume crops, Vicia faba belongs to those where the production of transgenic plants has not yet convincingly been reported. We have produced stably transformed lines of faba bean with an Agrobacterium tumefaciens-mediated gene transfer system. Stem segments from aseptically germinated seedlings were inoculated with A. tumefaciens strains EHA101 or EHA105, carrying binary vectors conferring (1) uidA, (2) a mutant lysC gene, coding for a bacterial aspartate kinase insensitive to feedback control by threonine, and (3) the coding sequence for a methionine-rich sunflower 2S-albumin, each in combination with nptII as selectable marker. Kanamycin-resistant calluses were obtained on callus initiation medium at a frequency of 10–30%. Shoot regeneration was achieved on thidiazuron containing medium in a second culture step. A subsequent transfer of shoots to BA-containing medium was necessary for stem elongation and leaf development. Shoots were rooted or grafted onto young seedlings in vitro and mature plants were recovered. Molecular analysis confirmed the integration of the transgenes into the plant genome. Inheritance and expression of the foreign genes was demonstrated by Southern blot, PCR, western analysis and enzyme activity assays. Although at present the system is time-consuming and of relatively low efficiency, it represents a feasible approach for the production of genetically engineered faba beans.     

Molecular heterogeneity and genetics of Vicia faba seed storage proteins

Summary Legumin and vicilin were purified from seeds of Vicia faba L. var. Scuro, characterized in different electrophoretic systems, and used to produce polyclonal antibodies in rabbits. Two-dimensional electrophoretic studies showed a wide range of heterogeneity in the subunits of both legumin and vicilin. Legumin was found to be composed of 29 disulphide-linked subunit pairs with different molecular weight and/or isoelectric point. Western blot analysis of legumin of several mutants revealed molecular polymorphism based on a corresponding gene family. Three different -major legumin patterns were found, and inheritance studies showed that the 34.3-kD legumin polypeptide is the product of one locus, Lg-1, which is the first legumin genetic locus described in Vicia faba. Vicilin was found to be composed of as many as 59 subunits distributed in a molecular weight range of 65.7 to 42.8 kD (major polypeptides) and 37.2 to 15.2 kD (minor polypeptides), with different isoelectric points. A model is proposed that explains the possible formation of the minor subunits and the major subunits of 48.2 and 46 kD molecular weight (MW) from proteolytic cleavages and/or glycosilation of precursor polypeptides. Ten different vicilin electrophoretic patterns were observed among the analyzed accessions, which showed large molecular polymorphism that proved to be under genetic control.Contribution no. 55 from the Center of Vegetable Breeding, Portici, Italy     

Genetics and mapping of new isozyme loci in Vicia faba L using trisomics

Polymorphism in ten enzyme systems (ACO, ACP, AAT, EST, FK, ME, NAG, PRX, 6PGD, and SOD) in Vicia faba L. was analyzed, revealing 13 loci, six of which have not been reported before. Inheritance, genetics, possible location, and linkage analysis were studied in 13 different F² populations trisomic for four of the six chromosomes (nos. 3, 4, 5, and 6) of the species. Each of these loci exhibited typical Mendelian inheritance except for those involved in the trisomic chromosome. Five loci have been assigned to a specific chromosome: Est-2 to chromosome 3, Fk-2 to chromosome 4, Prx-1 to chromosome 5, and Sod-1 and Pgd-p to chromosome 6. Nag-1 and Pgd-c displayed a linkage of 22.8 cM indicating a clear homology with chromosome 5 of garden pea on which both markers are syntenic.     

The legumin gene family: a reconstructed Vicia faba legumin gene encoding a high-molecular-weight subunit is related to type B genes

Nucleotide sequence information from a partial genomic clone, a cDNA clone, a RACE clone and a PCR fragment was combined to reconstruct the first reported complete gene sequence encoding a large legumin subunit, designated LelB3. The length difference to the well-characterized major legumin subunits is caused by an extended glutamin/glutamic acid-rich region encoded by the C-terminal part of the chain. Amino acid sequence comparisons reveal that gene LelB3 is more closely related to B-type than to A-type legumin genes of Vicia faba. Gene LelB3 is a member of a small gene family as indicated by published (Pich and Schubert, Biol Zbl 112 (1993); 342–350) and limited own data.     

Isozyme gene markers in Vicia faba L.

Summary This study was conducted to assess the genetic basis of the variability observed for the glutamate oxaloacetate transaminase (GOT), Superoxide dismutase (SOD), esterase (EST), and malate dehydrogenase (MDH) isozyme systems in different open-pollinated Vicia faba varieties. Individual plants showing contrasting zymogram patterns were simultaneously selfed and cross-combined. Crossing was unsuccessful in producing progeny, and only selfed progenies were suitable for genetical analysis of isozyme variability. Three zones of GOT activity were made visible. The isozyme of GOT-2 and GOT-3 zones were dimeric and under the control of three alleles at the Got-2 locus and two alleles at the Got-3 locus, respectively. The isozymes of the GOT-1 zone did not show any variability. Three zones of SOD isozyme activity were made visible. The isozymes occurring in the SOD-1 (chloroplastic isozyme form) and SOD-2 (cytosol isozyme form) zones were dimeric and under the control of two alleles at the Sod-1 and Sod-2 loci. The isozyme visualized in the SOD-3 zone (mitochondrial isozyme form) were tetrameric and under the control of two alleles at the Sod-3 locus. Apparently the isozymes made visible in the most anodal esterase zones EST-1, EST-2, and EST-3 were monomeric, and the occurrence of two alleles at each of two different loci explained the variability observed in the EST-2 and EST-3 zones. For MDH, only two five-banded zymogram pattern types were found, and every selfed progeny showed only one of the two zymogram type, indicating that each individual possessed fixed alleles at the loci controlling MDH isozyme. Got-2, Got-3, Sod-1, Sod-2, and Sod-3 appear to be five new isozyme gene markers that can be useful in Vicia faba breeding for linkage study, varietal fingerprinting, outcrossing rate estimate, and indirect selection for quantitative characters.     

Intraspecific unilateral incompatibility in Vicia faba L.

Summary Unilateral incompatibility was discovered when crossing was attempted between different self-compatible types and subspecies of V. faba. Crossing in the direction female less self-fertile x male more self-fertile failed, whereas the reciprocal-crossing succeeded. Unilateral incompatibility developed with the evolution of less fertile and large seeded field bean types. How a cross fertilized (and self-incompatible) system may develop from a self fertilized one is discussed.The unilateral incompatibility in V. faba and other plant species is compared. The two-power competition hypothesis can explain all kinds of unilateral incompatibility reported so far in the literature. Breeding field beans for improved self-fertility is discussed.     

Cytoplasmic male sterility in Vicia faba L.

Summary In many higher plants, nucleo-cytoplasmic interactions lead to pollen abortion. In Vicia faba, cytoplasmic male sterility is unstable as the cytoplasm appears to shift from a sterile to a fertile state. In this report, five flower phenotypes are defined but the study is focussed on the progenies obtained from intermediate, semi-sterile plants with the same homozygous nuclear constitution during five successive generations. The results could be interpreted by quantitative modifications of at least four different kinds of cytoplasmic determinants.     

Somatic embryogenesis in Vicia faba L.

The paper describes a method of somatic embryo induction in callus and suspension cultures of Vicia faba L. Callus was induced from immature cotyledons (green maturity stage) of white-flowering horse bean lines cultured on L2 medium (Phillips and Collins 1979) supplemented with 1% sucrose, 0.7% agar and different concentrations of 2,4-dichlorophenoxyacetic acid. The medium with 2.5 M 2,4-Dichlorophenoxyacetic acid was found optimum for embryogenic callus induction. Somatic embryos developed after transfer of the callus to media lower or zero 2,4-Dichlorophenoxyacetic acid and increased level of sucrose (2.5%). The release of somatic embryos from the callus was more apparent after transfer to liquid medium. There were various stages of somatic embryo development, i.e. globular, heart-shaped and torpedo ones.     

Flow karyotyping and sorting of Vicia faba chromosomes

Summary Chromosome suspensions were prepared from formaldehyde-fixed, synchronized Vicia faba root tips. After staining with the DNA intercalating fluorochrome propidium iodide, the suspensions were analysed with a flow cytometer. The resulting histograms of integral fluorescence intensity contained peaks similar to those of theoretical V.faba flow karyotypes. From V. Faba cv Inovec (2n = 12) only one peak, corresponding to a single chromosome type (metacentric chromosome), could be discriminated. However, it was found that the peak also contained doublets of acrocentric chromosomes. Bivariate analysis of fluorescence pulse area (chromosome DNA content) and fluorescence pulse width (chromosome length) was necessary to distinguish the metacentric chromosome. To achieve a high degree of purity, a two-step sorting protocol was adopted. During a working day, more than 25 000 metacentric chromosomes (corresponding to 0.2 g DNA) were sorted with a purity of more than 90%. Such chromosomes are suitable for physical gene mapping by in situ hybridization or via the polymerase chain reaction (PCR) and allow the construction of chromosome-specific DNA libraries. While it was only possible to distinguish and sort one chromosome type from V. Faba cv Inovec with the standard karyotype, it was possible to sort with a high degree of purity five out of six chromosome types of the line EFK of V. Faba, which has six pairs of morphologically distinct chromosomes. This result confirmed the possibility of using reconstructed karyotypes to overcome existing problems with the discrimination and flow sorting of individual chromosome types in plants.     

Purification and characterization of trypsin inhibitor from seeds of faba bean (Vicia faba L.)

A trypsin inhibitor from seeds of faba bean (Vicia faba L.) was purified to near homogeneity as judged by native-PAGE with about 11 % recovery using ammonium sulphate fractionation, ion-exchange chromatography on DEAE-cellulose and gel filtration through Sephadex G-100. The inhibitor had a molecular weight of 18 kD as determined by SDS-PAGE and Sephadex G-100. The inhibitor inhibited trypsin and chymotrypsin to the extent of 48 and 12 %, respectively. The inhibtion was of non-competitive type with dissociation constant for the enzyme inhibitor complex in the region of 0.07 mg·ml⁻¹. The inhibtor was stable between pH 4 and 5. It completely lost its activity when heated at 125 °C for 1 h or at 100 °C for 2 h. The inhibitor also lost its activity on exposure to 2-mercaptoethanol. Based on these properties, it could be concluded that Vicia faba trypsin inhibitor belongs to Bowman-Birk type of inhibitors, as it has molecular weight lower than generally observed for Kunitz type inhibitors.     

Studies on the movement and distribution of ethylene in Vicia faba L.

In Vicia faba ethylene does not appear to move between different parts of the plant in physiologically significant amounts. The resistance to longitudinal movement is such that lateral emanation effectively isolates different parts of the plant from each other. When emanation is prevented, ethylene can be channelled to any part of the plant. Exposure of one section of a plant to ¹⁴C-labelled ethylene (up to 200 l/l) increased the internal concentration in other parts with ethylene that did not originate from the feeding chamber. A basipetal gradient of endogenous ethylene concentration was found in the lacuna of intact plants, the source of ethylene being the stem tissue. The permeability of stem tissue to ethylene decreases with age. The concentration of ethylene in tissues surrounding the lacuna is always higher than that in the lacuna and it is argued that compartmentation of ethylene occurs within these tissues.