TEMPORAL AND SPATIAL COEXPRESSION OF HYDROGENASE AND NITROGENASE GENES FROM RHIZOBIUM-LEGUMINOSARUM BV VICIAE IN PEA (PISUM-SATIVUM L) ROOT-NODULES

Expression of the Rhizobium leguminosarum bv. viciae hydrogen uptake (hup) genes in pea root nodules has been studied by in situ hybridization. Accumulation of transcripts specific for the hydrogenase structural genes (hupSL) abruptly started at the beginning of the interzone II-III and continued throughout the nitrogen-fixing zone III. This accumulation paralleled that of nifA- and nifH-specific mRNAs, and hupSL mRNAs were detected in the same cells as nif mRNAs. This suggests that the signals or regulators that trigger nitrogenase expression in nodules are also responsible for hydrogenase induction. Mutations in several hydrogenase accessory genes did not affect the pattern of hupSL expression, suggesting that these genes are not involved in hydrogenase regulation.