IDENTIFICATION OF NOVEL PUTATIVE REGULATORY GENES INDUCED DURING ALFALFA NODULE DEVELOPMENT WITH A COLD-PLAQUE SCREENING-PROCEDURE

Until now very few plant genes with possible regulatory functions duri ng nodule development have been isolated, We have used a modified cold -plaque screening method to identify new transcripts expressed at low levels that are induced during nodulation. Several clones were isolate d and characterized by their mRNA expression patterns during nodule de velopment and in spontaneous nodules, Sequence homology with known gen es of other organisms indicated that transcripts corresponded to (i) ' 'basic'' genes probably required during the growth of the nodule organ (e.g., structural proteins), (ii) genes related to the metabolic adap tations taking place during nodule morphogenesis and function (e.g., c arbonic anhydrase), and (iii) genes containing regulatory motifs and/o r homologies (three clones out of the 20 identified). The latter genes encode a zinc-finger-containing protein, a putative protein kinase, a nd a Wilm's tumor (WT) suppressor homologue, respectively, Expression of the kinase and WT suppressor homologues was induced early in nodula tion, although the latter was activated transiently. Accumulation of t he Zn-finger gene transcripts was detected at a later stage of develop ment and seems to be regulated in a complex manner, Hence, using a col d-plaque screening procedure, we could identify genes that may play re gulatory roles in the signal transduction pathways activated during no dule development.