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Regulatory patterns of a large family of defensin-like genes expressed in nodules of Medicago truncatula

Nallu, Sumitha, Silverstein, Kevin A. T., Samac, Deborah A., Bucciarelli, Bruna, Vance, Carroll P., VandenBosch, Kathryn A.
Plos One 2013 v.8 no.4 pp. 1
Medicago truncatula, Rhizobium, gene expression regulation, genes, host plants, legumes, microarray technology, mutants, nitrogen-fixing bacteria, nodulation, promoter regions, root nodules
Root nodules are the symbiotic organ of legumes that house nitrogen-fixing bacteria. Many genes are specifically induced in nodules during the interactions between the host plant and symbiotic rhizobia. Information regarding the regulation of expression for most of these genes is lacking. One of the largest gene families expressed in the nodules of the model legume Medicago truncatula is the nodule cysteine-rich (NCR) group of defensin-like (DEFL) genes. We used a custom Affymetrix oligonucleotide microarray to examine the expression changes of 566 NCRs at different stages of nodule development. Additionally, rhizobial mutants were used to understand the importance of the rhizobial components in induction of NCRs. Expression of early NCRs was detected during the initial infection of rhizobia in nodules and expression continued as nodules became mature. Late NCRs were induced concomitantly with bacteroid development in the nodules. The induction of early and late NCRs was correlated with the number and morphology of rhizobia in the nodule. Conserved 41 to 50 bp motifs identified in the upstream 1,000 bp promoter regions of NCRs were required for promoter activity. These cis-element motifs were found to be unique to the NCR family among all annotated genes in the M. truncatula genome, although they did contain sub-regions with clear similarity to known regulatory motifs involved in nodule-specific expression and temporal gene regulation.