Guardians or Gateways? The Intricate Relationship Between Plant Cell Walls and Pathogenic Xanthomonas

ABSTRACT

Plants have evolved a complex cell wall (CW) providing support and protection against environmental constraints, including constant attacks from pests and pathogens. Indeed, the plant CW serves as both a physical barrier and a sophisticated monitoring and signalling system, making it a central component of plant immunity. The Xanthomonas genus encompasses a large diversity of plant‐pathogenic bacteria that, together, can infect a wide range of more than 400 plant species including monocots and dicots. Remarkably, Xanthomonas species are subdivided into highly specialized pathovars infecting a narrow range of plant species and/or tissues, each possessing a distinct CW structure and composition. This diversity makes Xanthomonas a perfect case for studying the interactions between bacterial pathogens and the plant CW. In this review, we provide an overview of the intricate interactions between Xanthomonas and the plant CW during the infection process. During infection, Xanthomonas degrades the plant CW both directly by using CW degrading enzymes and indirectly by reprogramming the plant transcriptome to enhance the expression of plant CW modifying enzymes. This degradation of the plant CW plays a central role during infection. On the plant side, it triggers immune responses, while on the Xanthomonas side, it facilitates bacterial invasion and access to nutrients, and activates a signalling hub that primes the pathogen for host colonization.