Use of enhancer trapping to identify pathogen‐induced regulatory events spatially restricted to plant–microbe interaction sites

Abstract

Plant genes differentially expressed during plant-pathogen interactions can be important for host immunity or can contribute to pathogen virulence. Large-scale transcript profiling studies, such as microarray- or mRNA-seq-based analyses, have revealed hundreds of genes that are differentially expressed during plant-pathogen interactions. However, transcriptional responses limited to a small number of cells at infection sites can be difficult to detect using these approaches, as they are under-represented in the whole-tissue datasets typically generated by such methods. This study examines the interactions between Arabidopsis thaliana (Arabidopsis) and the pathogenic oomycete Hyaloperonospora arabidopsidis (Hpa) by enhancer trapping to uncover novel plant genes involved in local infection responses. We screened a β-glucuronidase (GUS) reporter-based enhancer-trap population for expression patterns related to Hpa infection. Several independent lines exhibited GUS expression in leaf mesophyll cells surrounding Hpa structures, indicating a regulatory response to pathogen infection. One of these lines contained a single enhancer-trap insertion in an exon of At1g08800 (MyoB1, Myosin Binding Protein 1) and was subsequently found to exhibit reduced susceptibility to Hpa. Two additional Arabidopsis lines with T-DNA insertions in exons of MyoB1 also exhibited approximately 30% fewer spores than wild-type plants. This study demonstrates that our enhancer-trapping strategy can result in the identification of functionally relevant pathogen-responsive genes. Our results further suggest that MyoB1 either positively contributes to Hpa virulence or negatively affects host immunity against this pathogen.

The Second Intron Is Essential for the Transcriptional Control of the Arabidopsis thaliana GLABRA3 Gene in Leaves

“…To study the expression pattern mediated by this construct we fused the GUS marker gene directly after the second intron. As the signal levels were very low when using X-Gluc as a substrate, we used the more sensitive magenta-Glc-A as a substrate ( Schroeder et al, 2016 ). We detected GL3 expression in young leaves in all stages of trichome development Figures 4A,B ).…”

“…GUS stainings were essentially done as previously ( Sessions et al, 1999 ; Schroeder et al, 2016 ). After staining for 16 h at 37°C, tissues were cleared and leaves were inspected by light microscopy and pictures taken using the DISKUS software (Carl H. Hilgers -Technisches Büro, Germany).…”

Update on Myosin Motors: Molecular Mechanisms and Physiological Functions

“…In this case, the oomycete Hyaloperonospora arabidopsidis showed reduced infectivity in mutants that lack MyoB1 (Schroeder et al, 2016), indicating that this myosin interactor plays an important role in the infection process. Interestingly, the pathogen locally induced the expression of MyoB1, presumably to support its own growth on the plant host.…”

“…This novel function of MyoB1 seems to contradict the role of myosins in defending against ascomycete pathogens, but it is not known whether this function is related to MyoB1's role in binding myosin motors to cargo membranes. In this context, it is important to note that the resistant phenotype of myob1 mutants manifests itself already as a single mutant (Schroeder et al, 2016), whereas growth defects are detectable only in the case of multiple MyoB knockouts (Peremyslov et al, 2013), suggesting that the involvement in pathogen responses is unique for MyoB1. It will be interesting to determine the cellular defect(s) in myob1 that allows H. arabidopsidis to colonize Arabidopsis more readily and whether any myosin mutants also show a similar phenotype.…”