THE TEMPORAL AND SPATIAL TRANSCRIPTION PATTERN IN ROOT-NODULES OF VICIA-FABA NODULIN GENES ENCODING GLYCINE-RICH PROTEINS

Four different transcript sequences encoding gene products with an unu sually high glycine content were identified in Vicia faba root nodules . Northern blot analysis revealed a strong nodule specific expression of the corresponding genes. Time course experiments showed that two of these genes were transcribed before the onset of leghemoglobin expres sion and hence were designated VfENOD-GRP2 and VfENOD-GRP5, whereas th e first detection of VfNOD-GRP1 and VfNOD-GRP4 transcripts coincided w ith the appearence of leghemoglobin transcripts in V. faba root nodule s. A characteristic feature of all encoded nodulins was a hydrophobic N-terminus, which in the case of the nodulins ENOD-GRP2 and ENOD-GRP5 has the characteristics of a signal peptide. Such a structure is compa rable to other plant glycine-rich proteins decribed as components of t he plant cell wall. Based on tissue print hybridizations, we found tha t VfNOD-GRP1, VfENOD-GRP2 and VfNOD-GRP4 were expressed in the interzo ne II-III and in the whole nitrogen-fixing zone III. In contrast to Vf ENOD-GRP2 and VfNOD-GRP4, the signal intensity of hybridizing VfNOD-GR P1 transcripts was slightly reduced in the more proximal part of broad bean root nodules. Apart from the interzone II-III and the nitrogen f ixing zone III, VfENOD-GRP5 RNA was also detected in large areas of th e prefixing zone II.