| Summary: | <p>Abstract</p> <p>Background</p> <p>Plant natriuretic peptides (PNPs) are a class of systemically mobile molecules distantly related to expansins. While several physiological responses to PNPs have been reported, their biological role has remained elusive. Here we use a combination of expression correlation analysis, meta-analysis of gene expression profiles in response to specific stimuli and in selected mutants, and promoter content analysis to infer the biological role of the <it>Arabidopsis thaliana </it>PNP, AtPNP-A.</p> <p>Results</p> <p>A gene ontology analysis of <it>AtPNP-A </it>and the 25 most expression correlated genes revealed a significant over representation of genes annotated as part of the systemic acquired resistance (SAR) pathway. Transcription of these genes is strongly induced in response to salicylic acid (SA) and its functional synthetic analogue benzothiadiazole S-methylester (BTH), a number of biotic and abiotic stresses including many SA-mediated SAR-inducing conditions, as well as in the constitutive SAR expressing mutants <it>cpr5 </it>and <it>mpk4 </it>which have elevated SA levels. Furthermore, the expression of <it>AtPNP-A </it>was determined to be significantly correlated with the SAR annotated transcription factor, <it>WRKY 70</it>, and the promoters of <it>AtPNP-A </it>and the correlated genes contain an enrichment in the core WRKY binding W-box <it>cis</it>-elements. In constitutively expressing <it>WRKY 70 </it>lines the expression of <it>AtPNP-A </it>and the correlated genes, including the SAR marker genes, <it>PR-2 </it>and <it>PR-5</it>, were determined to be strongly induced.</p> <p>Conclusion</p> <p>The co-expression analyses, both in wild type and mutants, provides compelling evidence that suggests <it>AtPNP-A </it>may function as a component of plant defence responses and SAR in particular. The presented evidence also suggests that the expression of <it>AtPNP-A </it>is controlled by WRKY transcription factors and WRKY 70 in particular. <it>AtPNP-A </it>shares many characteristics with PR proteins in that its transcription is strongly induced in response to pathogen challenges, it contains an N-terminal signalling peptide and is secreted into the extracellular space and along with PR-1, PR-2 and PR-5 proteins it has been isolated from the Arabidopsis apoplast. Based on these findings we suggest that <it>AtPNP-A </it>could be classified as a newly identified PR protein.</p>
|
|---|