| dc.description.abstract | The plant microbiome can help the plant mitigate biotic stress. Hpa associated microbiota (HAM) are beneficial bacteria for which it is proven that Arabidopsis thaliana can actively recruit them in response to infection with the obligate biotrophic pathogen Hyaloperonospora arabidopsidis (Hpa). Furthermore, the HAM have been shown to suppress Hpa infection as part of the “soil-borne legacy” of generationally transmitted disease resistance. The mechanism behind this phenomenon is still poorly understood. On the plant side, secretion of root exudates such as coumarins has been identified as one mechanism for selection of beneficials. However, the mechanisms from the microbe side of the interaction are less understood, although it is known that Xanthomonas ASV a0e1a seems to be an important HAM member. A recent study by Goossens et al. (2023), showed that this is the most prevalent HAM ASV and that it responds strongly to Hpa infection. This study aims to investigate which genes in Xanthomonas sp. WCS2014-23 (representative of ASV a0e1a) are important for its recruitment to the phyllosphere of Arabidopsis during aboveground infection of Hpa. To investigate this, we created an INSeq mutant library in WCS2014-23 via transposon insertion mutagenesis. Subsequently, this library was utilised in multiple mutant screens involving recruitment experiments to identify candidate recruitment genes.
Our INSeq library had an insertion density of ~58%, which corresponds to insertions in ~50.6 to ~72.2% of the 4399 predicted coding sequences present in the reference genome. We identified 63 potential recruitment genes. The most promising candidates fall under three categories. The first two categories relate to the physical process of recruitment, “Perception & Regulation” and “Movement”. The last category, “Antagonism” relates to the interaction with Hpa which included suppressing the infection combined with co-occurring in the phyllosphere. These genes fit a scenario where Xanthomonas perceives an Hpa-infected plant and activates a process inside the bacterium which causes its movement to the phyllosphere. Once arrived at the sites of infection, the bacterium uses certain mechanisms to repress Hpa and reduce infection. With this research we provide insight into which genes of beneficial microbes could be involved in their recruitment to the plant in response to a foliar pathogen infection, while also providing leads for further research into beneficial plant-microbe interactions. Additionally, insight into how HAM are able to suppress Hpa could contribute to the development of new strategies for reducing crop losses due to Hpa infection. This could potentially include the development of bioinoculants with beneficial bacteria which could replace environmentally unfriendly, chemical pesticides. | |
