SYMBIOTIC GENE SYM31 CONTROLS THE PRESENCE OF A LECTIN-LIKE GLYCOPROTEIN IN THE SYMBIOSOME COMPARTMENT OF NITROGEN-FIXING PEA NODULES

The distribution of a lectinlike glycoprotein, PsNLEC-1, was examined with a specific antiserum in nodule tissue from a symbiotically defect ive pea mutant, Sprint2Fix(-) (sym31), and the parent line, Sprint2. I mmunostaining of Western blots (immunoblots) revealed that, whereas wi ld-type nodules contained three antigenic isoforms of PsNLEC-1, nodule homogenates of mutant sym31 contained only one isoform, PsNLEC-1C. Fr actionation studies indicated that PsNLEC-1C was not associated with s ymbiosomes in either the mutant or the wild-type parent (unlike the ot her two isoforms from wild-type nodules), Light microscopy revealed th at PsNLEC-1 antigen was more abundant in the infected tissues of wild- type nodules than in nodules of sym31. By contrast, in situ hybridizat ion indicated that the PsNlec1 gene transcript was strongly expressed in infected cells of both Sprint2 and sym31 nodule tissues. At the ult rastructural level, most of the PsNLEC-1 antigen in sym31 nodule tissu e was visualized as inclusion bodies in the vacuolar compartment of in fected host cells but it was apparently absent from the symbiosome com partment. The results suggest an aberrant vesicle targeting pathway du ring symbiosome development in this mutant.