Mechanism of WRKY factors-mediated defense and heterosis in Arabidopsis polyploids

Heterosis or hybrid vigor describes the development of superior traits in progeny from crosses between two different species. Although this phenomenon is commonly used for improving yield and quality of agricultural crops, the genetic and molecular mechanisms surrounding hybrid vigor remain elusive. Genetically, several hypotheses have been used to explain the basis of heterosis. This includes the dominance, overdominance, pseudo- overdominance, and epistasis models. In an interspecific cross between a synthetic autotetraploid Arabidopsis thaliana (At4) and a natural autotetraploid Arabidopsis arenosa (Aa), a genome-wide change in gene expression was detected in the synthetic Arabidopsis suecica allotetraploid hybrids (Allo733) when compared to the progenitors. Increased biomass, starch accumulation and disease resistance were observed in Allo733 when compared to its parents. The availability of these related Arabidopsis species and the establishment of the synthetic allotetraploids thus provide an excellent and tractable genetic system for studying the mechanism of hybrid vigor. WRKY transcription factors are a family of plant-specific transcriptional regulators involved in diverse plant signaling pathways such as pathogen responses, abiotic stress responses, seed development and senescence processes. The ability of plants to develop multiple interconnected pathways to cope with the constant changes of environments and to fend off their attackers is vital for their successful survival and propagation. Therefore, modulation of defense regulatory pathways could contribute to the improved vigor in the allotetraploids. The goal of the proposed research is elucidate the molecular mechanism of heterosis through studying the evolution and modulation of WRKY factors upon genome divergence and hybridization in the related Arabidopsis autotetraploids and allotetraploids. To achieve this, we will first examine the kinetics of WRKY expression in the related Arabidopsis species and allotetraploids. The epigenetic and genetic control of WRKY genes expression upon biotrophic pathogen (Pseudomonas syringae) or chemical (salicylic acid) treatment over different time intervals will be analyzed. Using biochemical and genetic approaches, we will further dissect possible protein-protein or protein-DNA interactions among homologous AtWRKY and AaWRKY factors or between WRKYs and their target promoters. The proposed studies are expected to provide insights to the mechanisms of heterosis and further our understanding in the modulations of defense response pathways in allotetraploid hybrids. In addition, knowledge gained will have potential application in crop biotechnology.