Abstract
Garden pea (Pisum sativum L.) is a globally important legume crop. Like other legumes, it forms beneficial symbiotic interactions with the soil bacteria rhizobia, gaining the ability to fix atmospheric nitrogen. In pea nodules, the meristem is long-lasting and results in the formation of several histological zones that implicate a notable differentiation of infected host cells. However, the fine transcriptional changes that accompany differentiation are still unknown. In this study, using laser microdissection followed by RNA-seq analysis, we performed transcriptomic profiling in the early infection zone, late infection zone, and nitrogen fixation zone of 11-day-old nodules of pea wild-type line SGE. As a result, a list of functional groups of differentially expressed genes (DEGs) in different nodule histological zones and a list of genes with the most prominent expression changes during nodule development were obtained. Their analyses demonstrated that the highest amount of DEGs was associated with the nitrogen fixation zone. Among well-known genes controlling nodule development, we revealed genes that can be novel players throughout nodule formation. The characterized genes in pea were compared with those previously described in other legumes and their possible functions in nodule development are discussed.
Highlights
Legumes play an important role in agrocenoses owing to their unique ability to enrich the soil with nitrogen
Hierarchical clustering using sample-to-sample distances showed distinct grouping of biological replicates within samples; early and late infection zones were more similar to each other and the nitrogen fixation zone was closer to the late infection zone (Figure 2B)
The most prominent expression changes were associated with cells from the nitrogen fixation zone, which differed from cells of both early and late infection zones in the number of differentially expressed genes (DEGs), whereas the contrast between early and late infection zones showed fewer DEGs
Summary
Legumes play an important role in agrocenoses owing to their unique ability to enrich the soil with nitrogen. They are able to form a new organ, a nitrogen-fixing nodule, as a result of interaction with the soil bacteria rhizobia. In this organ, a low oxygen concentration is maintained, which is required for nitrogenase activity, the main enzyme of nitrogen fixation. The perception of plant flavonoids by rhizobia leads to transcriptional activation of their nodulation (nod) genes, resulting in the production of specific lipo-chitooligosaccharide signaling molecules (Nod factors) [1]. Bacteria infect primordium cells that later form the nodule
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