|Samac, Deborah - Debby|
Submitted to: Plant Physiology
Publication Type: Abstract Only
Publication Acceptance Date: 6/1/1995
Publication Date: N/A
Technical Abstract: Phosphoenolpyruvate carboxylase (PEPC) plays a crucial role in the assimilation of CO2 during symbiotic N2 fixation in legume root nodules. The product of the PEPC catalyzed reaction, oxaloacetate, serves several functions. Some is converted to malate which is used by bacteroids as their primary carbon and energy source. Oxaloacetate also provides the carbon skeleton for the synthesis of aspartate and asparagine, particularly important in amide transporting legumes such as alfalfa. We have isolated and characterized an alfalfa PEPC gene (PEPC-7) whose transcripts are found at elevated levels in nodules relative to either leaves or roots. The intron/exon structure of this gene is identical to other plant PEPC genes except for the presence of an additional intron in the 5 'untranslated region. A chimeric reporter gene was made that consists of 1277 base pairs of 5 '-flanking sequence (P6 promoter) fused to uidA, which encodes B-glucuronidase (GUS). When alfalfa and Lotus plants containing this transgene were regenerated and analyzed, strong GUS expression was found in both infected and uninfected cells of the symbiotic zone, in the nodule parenchyma, and in the cells associated with vascular bundles. In situ RNA hybridization studies, using RNA complementary to the 3' end of the PEPC-7 transcript as a probe, largely confirmed these observations. The P6 promoter construct also directs GUS expression to pollen and root tips. Analyses of constructs formed from deletion derivatives of the P6 promoter suggest that the region between -634 and -536 is of particular importance in directing transcriptional activity to the infected zone of nodules. Within this region is a mirror repeat sequence that is potentially capable of forming an H-DNA structure.