The endomicrobiome and weed invasiveness in Mediterranean ecosystems

Mediterranean ecosystems, one of the most significant global hotspots of biodiversity, are threatened by invasive weeds. Although endomicrobiomes – the vast array of microbes colonising living plant tissues – are known to affect plant fitness, their contribution to weed invasiveness remains virtually unknown. Here we experimentally assessed the role of the<b> </b>endomicrobiome in the microevolution of <i>Taraxacum</i> <i>officinale</i> (common dandelion), a widespread invasive weed in Mediterranean ecosystems worldwide. In a culling experiment across five generations, we compared the microevolutionary rates of <i>T. officinale</i> from Mediterranean ecosystems on five continents grown with intact or reduced native seed-borne endomicrobiomes. Additionally, we conducted a competition experiment with F₁ and F₅ individuals to assess their impacts on native local Asteraceae species. We found <i>T. officinale</i> individuals growing with their intact endomicrobiomes to exhibit faster and more positive trait evolution than individuals growing with reduced endomicrobiomes. Enhanced competitiveness of endomicrobiome-colonized <i>T. officinale </i>plants<i> </i>with local Asteraceae species was apparently caused by increased synthesis of allelochemicals in shoots and rhizosphere soil, with gene expression analyses also showing the endomicrobiome to affect the expression by <i>T. officinale</i> of stress response and RNA-directed DNA methylation genes. Our findings provide novel insights into the mechanisms underlying weed invasiveness in Mediterranean ecosystems, highlighting the endomicrobiome as a potent driving force in the evolutionary processes associated with plant invasion success.