Promoter analysis of members of a plant defense-related LRR-RLK gene cluster in Arabidopsis thaliana

M.Sc. (Biochemistry)A 14-member, closely-spaced cluster of genes coding for leucine-rich repeat receptor-like kinases (LRR-RLKs) is located on chromosome 1 of Arabidopsis thaliana. Following on from previous microarray studies that found some of the members of this cluster to be upregulated in response to biotic stressors, including the bacterial elicitor flg22, the present study sought to confirm, using a luciferase-based protoplast assay, that flg22 does in fact induce the expression of the genes, and then to investigate the promoters of the genes. The promoters of At1g51790, At1g51850 and At1g51890 responded positively in this particular assay, and bioinformatic analyses determined that W-boxes are over-represented in the cloned regions. Mutational inactivation of individual W-boxes in the promoter of At1g51790 drastically reduced the flg22 response, except for the W-box closest to the start site, which seemed to increase both basal and flg22-inducible expression. In the promoter of At1g51850, mutational inactivation of either or both of its W-box dyads resulted in virtually no flg22 inducibility. The deletion of 6 W-boxes in the promoter of At1g51890, done via truncation, drastically reduced both its basal expression and its inducible response to flg22. These results provide evidence that W-box cis-elements are responsible for the upregulation of these LRR-RLKs in response to flg22. WRKYs -7, -11, -22,and -26 were found bioinformatically to have similar expression patterns to some of the genes in the cluster, and are thus good candidates to investigate as transcriptional regulators of the cluster in future studies