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A linkage map of pea was constructed based on restriction fragment length polymorphism analysis of recombinant inbreds. The map derived from one cross used 151 markers spanning approximately 1,700 cM. Comparisons of three recombinant inbred populations showed that the map is not universal. At least one region of the genome could exist in several different linkage arrangements. These results indicate that some degree of caution should be exercised during the interpretation of various linkage maps derived for many organisms.

The pectinolytic enterobacterium Erwinia chrysanthemi 3937 causes a systemic disease in its natural host, the African violet (Saintpaulia: ionantha). It produces two structurally unrelated siderophores, chrysobactin and achromobactin. Chrysobactin makes a large contribution to invasive growth of the bacterium in its host. Insertion mutants of a chrysobactin-defective strain were constructed and screened on the universal CAS-agar medium used for siderophore detection. A set of mutants affected in the production of achromobactin were identified. This paper describes a mutant affected in the transport of all the ferrisiderophores used by the bacterium as iron sources. Molecular analysis revealed that the insertion mutation disrupts the tonB gene. The predicted Er. chrysanthemi TonB protein has a molecular mass of 27600 Da and shares 20-58% identity with the TonB proteins from 20 other bacterial species. The pathogenicity of the tonB mutant was assessed by inoculation of African violets. The impairment in the spread of symptoms was similar in the tonB mutant to that in chrysobactin-defective mutants. However, the pectinolytic activity, the major pathogenicity determinant in Er. chrysanthemi, appeared to be stimulated twofold in the tonB mutant.

The structure of a citrate siderophore named achromobactin isolated from the culture medium of Erwinia chrysanthemi was elucidated by spectroscopic methods and chemical degradation.

Erwinia chrysanthemi 3937 synthesizes an exopolysaccharide (EPS) composed of rhamnose, galactose, and galacturonic acid. Fourteen transcriptional fusions in genes required for EPS synthesis, named eps, were obtained by Tn5-B21 mutagenesis. Eleven of them are clustered on the chromosome and are repressed by PecT, a regulator of pectate lyase synthesis. In addition, expression of these fusions is repressed by the catabolite regulatory protein, CRP, and induced in low osmolarity medium. The three other mutations are located in genes that are not regulated by pecT. A 13-kb DNA fragment containing pecT-regulated eps genes has been cloned. All the genes identified on this fragment are transcribed in the same orientation and could form a large operon. The promoter region of this operon has been sequenced. It contains a JUMP-start sequence, a sequence required for the expression of polysaccharide-associated operons. E. chrysanthemi 3937 produces a systemic soft rot on its host Saintpaulia ionantha. An eps mutant was less efficient than the wild-type strain in initiating a maceration symptom, suggesting that production of EPS is required for the full expression of the E. chrysanthemi virulence.

A cDNA encoding the chloroplast/mitochondrial form of glutathione reductase (GR; EC 1.6.4.2) from pea (Pisum sativum L.) was used to map a single GR locus, named GOR1. In two domesticated genotypes of pea (cv. Birte and JI 399) it is likely that the GOR1 locus contains a single gene. However, in a semi-domesticated land race of pea (JI 281) two distinct but closely related sets of GR gene sequences were detected at the GOR1 locus. The extra GR sequences in JI 281 represent either a second intact gene or a partial or pseudogene copy. A GR gene was cloned from cv. Birte, sequenced and its structure analysed. No feature of the transcription or structure of the gene suggested a mechanism for generating any more than one form of GR. From these data plus previously published biochemical evidence we suggest that a second, distinct gene encoding for the cytosolic form of GR should be present in peas. The GOR1-encoded GR mRNA can be detected in all main organs of the plant and no alternative spliced species was present which could perhaps account for the generation of multiple isoforms of GR. The mismatch between the number of charge-separable isoforms in pea and the proposed number of genes suggests that different GR isoforms arise by some form of post-translational modification.

In planta expression of a high-affinity iron-uptake system involving the siderophore chrysobactin in Erwinia chrysanthemi 3937 contributes greatly to invasive growth of this pathogen on its natural host, African violets. A previous study reported that global regulation by iron in this strain was mediated at the transcriptional level via the cbr locus which, when inactivated by insertional mutation, prevents the chrysobactin system from being tightly repressed by FeCl3. Herein, we report the nucleotide sequence of this locus and the functional analysis of its encoded products. Sequence analysis of a 4.8 kb genomic segment of a plasmid encompassing the cbr locus and characterization of the cognate translated products made it possible to uncover a system exhibiting similarity with prokaryotic transporters implicated in the transport of iron complexes. Accordingly, the CbrA product was shown to be the periplasmic component of a permease complex also including two integral membrane proteins, CbrB and CbrC, and the ATP-binding unit CbrD. This system allowed internalization of Fe(III) when supplied to bacterial cells as 59FeCl3 or 59Fe dicitrate, via complexation to a second siderophore recently detected in strain 3937. Most notably, we demonstrate that this second siderophore-mediated iron-acquisition system is operational in bacterial cells grown in the presence of FeCl3. The regulatory effect of cbr was further assessed on a lacZ chrysobactin operon fusion indicating that the transcriptional control exerted by cbr on expression of the chrysobactin system is of homeostatic nature. in conclusion, E. chrysanthemi provides an interesting model in which iron acquisition involves an inductive process resulting in differential expression of two siderophore-mediated pathways in relation to external iron accessibility.