What lies beneath: belowground defense strategies in plants

• Root defense responses are less well studied than those in leaves.
• Root and leaf defense responses share many similarities as well as differences.
• Roots possess specialized structures as part of their defense response.
• The availability of plant and fungal genomes makes it an exciting era to study root responses.

Diseases caused by soil-borne pathogens result worldwide in significant yield losses in economically important crops. In contrast to foliar diseases, relatively little is known about the nature of root defenses against these pathogens. This review summarizes the current knowledge on root infection strategies, root-specific preformed barriers, pathogen recognition, and defense signaling. Studies reviewed here suggest that many commonalities as well as differences exist in defense strategies employed by roots and foliar tissues during pathogen attack. Importantly, in addition to pathogens, plant roots interact with a plethora of non-pathogenic and symbiotic microorganisms. Therefore, a good understanding of how plant roots interact with the microbiome would be particularly important to engineer resistance to root pathogens without negatively altering root-beneficial microbe interactions.