Nodulin Regulation in Common Bean Nodules Induced by Bacterial Mutants. Jaime E. Padilla. Bioloia Molecular de Plantas, Centro de Investigación sobre Fijación de Nitrógeno, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México. Juan Miranda, and Federico Sánchez. Bioloia Molecular de Plantas, Centro de Investigación sobre Fijación de Nitrógeno, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México.. MPMI 4:433-439. Accepted 24 April 1991. Copyright 1991 The American Phytopathological Society.

Nodulin expression was evaluated in nodules of common bean (Phaseolus vulgaris) induced by Rhizobium phaseoli mutants and an Agrobacterium transconjugant. Either noninfected, slow-developed, or ineffective nodules, or nodules arrested after bacterial release were formed. The expression levels of ENOD2, uricase-II, leghemoglobin (Lb), and nodulin-30 (Npv-30) transcripts were compared in nodules induced by wild type and mutant strains at initial (12 d) and terminal (21 d) developmental stages. Uricase-II mRNA was detected in “empty” nodules produced by three different mutants, suggesting an additional regulation of this nodulin during the early stages of nodulation. Accumulation of ENOD2 and uricase-II transcripts were observed in slow-developed but not in arrested nodules. Npv-30 and Lb mRNAs were only found in nodules containing infected cells; however, their relative levels differ depending on the nodule-inducing mutant. Ineffective strains produced nodules with similar initial development and nodulin gene expression, but decreased amounts of late nodulin transcripts at the terminal stage. Correlations that suggest conditions for the initial and coordinated regulation of nodulin expression in determinate-type nodules are discussed.