Differential regulation and interaction of homoeologous WRKY18 and WRKY40 in Arabidopsis allotetraploids and biotic stress responses.

WRKY transcription factors (TFs) belong to a large family of regulatory proteins in plants that modulate many plant processes. Extensive studies have been conducted on WRKY-mediated defense response in Arabidopsis thaliana and several crop species. Here, we aimed to investigate the potential roles and contributions of WRKY TFs in improving the defense response in the resynthesized Arabidopsis allotetraploids (Arabidopsis suecica) derived from two related autotetraploid progenitors, Arabidopsis thaliana (At4) and Arabidopsis arenosa (Aa). Rapid and differential induction of WRKY18 and WRKY40 expression was evident in response to Pseudomonas syringae and salicylic acid (SA) treatments in the allotetraploids. Selected direct targets of the WRKYs and PR1 also showed altered induction kinetics in the allotetraploids. Cleaved amplified polymorphic sequence analysis further revealed the accumulation of preferential homoeologous alleles (AtWRKY18, AaWRKY40, and AtWRKY60) in the allotetraploids, suggesting the potential for altered protein-protein interaction networks in the hybrids. Indeed, results showed that the cis-interacting AtWRKY18/AtWRKY18 homodimer or trans-interacting AtWRKY18/AaWRKY40 heterodimer exists as the preferred dimer interaction. Moreover, differential affinities of WRKY18 and WRKY40 homo- and heterodimers toward the W-boxes in the WRKY60 promoter were observed. Transient and stable expression of the selected WRKYs in transgenic Arabidopsis further supported the idea that differential interactions lead to changes in PR1 induction and direct target expression under stress, respectively. Our data suggest that differential expression as well as differences in the strength of protein-protein and/or protein-DNA interactions among the WRKY homoeologs could lead to altered regulatory networks of defense genes, contributing to improved defense in allotetraploids.