Characterization of a Casuarina glauca Nodule-Specific Subtilisin-like Protease Gene, a Homolog of Alnus glutinosa ag12

Abstract

In search of plant genes expressed during early interactions between Casuarina glauca and Frankia, we have isolated and characterized a C. glauca gene that has strong homology to subtilisin-like protease gene families of several plants including the actinorhizal nodulin gene ag12 of another actinorhizal plant, Alnus glutinosa. Based on the expression pattern of cg12 in the course of nodule development, it represents an early actinorhizal nodulin gene. Our results suggest that subtilisin-like proteases may be a common element in the process of infection of plant cells by Frankia in both Betulaceae (Alnus glutinosa) and Casuarinaceae (Casuarina glauca) symbioses.Additional keyword: symbiosis.

Casuarina glauca Prenodule Cells Display the Same Differentiation as the Corresponding Nodule Cells

“…In situ hybridization showed that cg12 is strongly expressed in prenodule cells where infection proceeds (Fig. 3A, B), the level of expression being similar to that found during infection of cortical cells of the young nodule lobe (Laplaze et al 2000). A lower signal was also detected in prenodule cells completely filled with Frankia.…”

“…The expression of a serine protease of the subtilase family (cg12 or ag12, respectively) is strongly induced in nodule cortical cells upon infection by Frankia (Ribeiro et al 1995;Laplaze et al 2000). cg12/ag12 expression in infected cells decreases at the onset of bacterial nitrogen fixation.…”

Transcriptomics of Actinorhizal Symbioses Reveals Homologs of the Whole Common Symbiotic Signaling Cascade

“…Around 1,500 unigenes (11%) for A. glutinosa and 2,000 unigenes (14%) for C. glauca were shown to be regulated or specifically induced during nodule development. In both species, it is worth noting that among the most highly induced genes (Table III), two previously characterized actinorhizal nodulins, a subtilase (Ag12/Cg12) and a dicarboxylate transporter (Agdcta1; Ribeiro et al, 1995;Laplaze et al, 2000;Svistoonoff et al, 2003;Jeong et al, 2004), were identified. More detailed data analysis enabled us to identify other known A. glutinosa nodulins with homologs in C. glauca.…”

“…Interestingly, Ag12 (for A. glutinosa12) and Cg12 (for C. glauca12) were among the most strongly induced genes in nodules (Table III). These two homologs encode a subtilase, considered a nodulin linked to symbiosis (Ribeiro et al, 1995;Laplaze et al, 2000;Svistoonoff et al, 2003). Two other actinorhizal nodulins were also found in both species among the top-20 induced genes: a dicarboxylate transporter (Dcat1) that could supply the intracellular bacteria with carbon, and a g-expansin natriuretic peptide belonging to a novel class of peptide signal molecules (plant natriuretic peptides) involved in biotic and abiotic stress response.…”

“…On the other hand, a number of genes have been shown to be up-regulated in response to interaction with Frankia (Pawlowski, 2009). These genes include an enolase (van Ghelue et al, 1996), a subtilisin-like protease (Laplaze et al, 2000), a dicarboxylate transporter (Jeong et al, 2004), and nitrogen assimilation genes (Guan et al, 1996) as well as numerous poorly characterized genes.…”