Search

The pea mutant line P55 is defective in root nodule formation, and this phenotype is controlled by a single recessive gene. Complementation analysis revealed that the mutation in P55 is allelic to sym19, which has previously been mapped to linkage group I. Detailed mapping revealed that the sym19 and ENOD40 loci are separated by 2.7 cM. We identified four recombination events, demonstrating that the nodulation defect caused by mutation of the sym19 locus cannot be due to mutation of ENOD40. RT-PCR experiments showed that P55 expresses ENOD12A, but there was little or no increase in the level of its transcript in response to Nod factor or infection with Rhizobium. To investigate this expression pattern further, transgenic peas carrying a pENOD12A-GUS reporter construct were made. One transgenic line was crossed with line P55, to generate F2 progeny homozygous for sym19 and carrying pENOD12A-GUS. In both WT and sym19 mutant lines, ENOD12A-GUS expression was induced at sites of lateral root emergence in uninoculated plants. In Nod+ plants pENOD12A-GUS was induced in response to Rhizobium leguminosarumn bv. viciae, but no such induction was seen in the Nod- (sym19) mutants.

Several mutants defective in the nodulation process during rhizobial or endomycorrhizal endosymbiosis of pea have been identified previously. We have integrated the map positions of two such nodulation mutations, sym9 and sym10, into the molecular map of pea by applying molecular-marker techniques combined with bulked segregant analysis (BSA). Lines P2 and P54 were found to carry alleles of sym9, line P56 carried an allele of sym10. F2 populations were derived from crosses of P2, P54 and P56, to JI281 and JI15, two of the parental lines that have been used previously to generate a molecular map of pea. sym9 was located on linkage group IV by AFLP-BSA analysis and subsequently mapped by RFLP in both F2 populations, P2 × JI281 and P54 × JI281. RFLP-BSA analysis was applied to assign sym10 to linkage group I. The RFLP marker locus, chs2, co-segregates with sym10 in the F2 population of P56 × JI15. [ABSTRACT FROM AUTHOR]