A latitudinal gradient of host specialization in plant leaf-bacteria symbiosis

Abstract

Host specialization is a common phenomenon in host-microbe symbiosis and plays a critical role in the ecology and evolution of both hosts and symbionts. However, explaining the origins and maintenance of host specialization in aboveground plant-bacteria symbiosis remains challenging. Theories have predicted that host specialization is associated with genome streamlining of symbiont bacteria, affected by bacterial horizontal transmission among host species, and contributes to symbiont diversity along latitudinal gradients. Here we tested these hypotheses by quantifying the host specificity and community composition of plant leaf bacteria symbioses for 329 tree species across a latitudinal gradient. Most bacteria associated with plant leaves were host specialized. The degree of host specificity was phylogenetically conserved and negatively correlated with bacterial genome size. We found that phyllosphere bacteria associated with locally abundant plant species are more widespread and less host-specialized than rare plant species-associated bacteria, potentially resulting from bacterial horizontal transmission among plant species. Finally, we showed that phyllosphere bacteria are more host-specialized and have smaller genome size at lower latitudes. Overall, our study provided in situ evidence for the importance of genome streamlining and host species abundance in the evolution of host specialization of leaf-associated symbioses, and highlighted a latitudinal gradient of host specialization that potentially explained the incredible diversity of plant-bacteria symbioses in the tropics.

Zihui Wang

Postdoctoral Fellow

I’m interested in understanding the factors that shape plant-microbial associations and predict their distribution and function under global change.