Co-expression analysis identifies putative targets for CBP60g and SARD1 regulation

Gene expression profiling on a custom microarray identified a set of genes, like SID2, down-regulated in cbp60g sard1 mutant plants. Co-expression analysis across a defined set of ATH1 full genome microarray experiments expanded this gene set; clustering analysis was then applied to group densely interconnected genes. A stringent threshold for co-expression identified two related calmodulin-like genes tightly associated with SID2. SID2 was found to cluster with genes whose promoter regions were significantly enriched with GAAATT motifs. Genes clustering with SID2 were found to be down-regulated in the cbp60g sard1 double mutant. Representative genes from other clusters enriched with the GAAATT motif were found to be variously down-regulated, unchanged or up-regulated in the double mutant. A previously characterised co-expression between SID2 and WRKY28 was not reproduced in this analysis but was contained within a subset of the experiments where SID2 was co-expressed with CBP60g or SARD1.Putative components of the CBP60g SARD1 signalling network have been uncovered by co-expression analysis. In addition to genes whose regulation is similar to that of SID2 some are repressed by CBP60g and SARD1.Two principal mechanisms, with overlapping components, exist to protect plants from infection. Pattern triggered immunity (PTI) involves the recognition of conserved, indispensible microbial structures, such as flagellin. These Microbe Associated Molecular Patterns (MAMPs) are recognised by Pattern Recognition Receptors (PRRs) such as FLS2, which recognizes flagellin, and stimulate a signalling network to elaborate an appropriate defence. In order to break free of this basal immune response adapted pathogens must produce and deliver effectors capable of disarming the plants surveillance and countermeasures. The second mechanism of protection therefore is Effector Triggered Immunity (ETI) whereby plants monitor effectors or their targets with Resistance (R) gene products. Recog