Differential regulation of the durum wheat Pathogenesis-related protein (PR1) by Calmodulin TdCaM1.3 protein

In plants, pathogenesis-related 1 protein (PR1) is considered as important defense protein. The production and accumulation of PR proteins in plants are one of the important responses to several biotic and abiotic stresses. In this regard, PR1 gene was isolated from Triticum turgidum ssp durum and was named as TdPR1.2. The amino acid sequence of TdPR1.2 protein showed 100%, 97.13%, and 44.41% with known PR1 proteins isolated from Triticum aestivum TdPR1-18, PRB1.2 of Aegilops tauschii subsp. tauschii and Arabidopsis thaliana respectively. qRT-PCR showed that TdPR1.2 was induced specially in leaves of durum wheat treated with Salicylic acid for 48 h. Besides, bioinformatic analysis showed that the durum wheat TdPR1.2 harbors a calmodulin binding domain located in it's C-terminal part and that this domain is conserved among different PR1 proteins isolated so far. However, no information is available about the regulation of PR genes by calmodulin and Ca²⁺ complex (CaM/Ca²⁺). Here, we showed that TdPR1.2 gene exhibits an antibacterial effect as revealed by the in vitro tests against 8 different bacteria and against the fungi Septoria tritici. In addition, we demonstrate for the first time that PR1 proteins are able to bind to CaM in a Ca²⁺-dependent manner via a GST-Pull down assay. Finally, in presence of Mn²⁺ cations, CaM/Ca²⁺ complex stimulated the antimicrobial effect of TdPR1.2. Such effects were not reported so far, and raise a possible role for CaM/Ca²⁺ complex in the regulation of plant PRs during cellular response to external signals.