Unraveling the dynamics of Xanthomonas' flagella: insights into host-pathogen interactions

Abstract

Understanding the intricate interplay between plants and bacteria is paramount for elucidating mechanisms of immunity and disease. This review synthesizes current knowledge on the role of flagella in bacterial motility and host recognition, shedding light on the molecular mechanisms underlying plant immunity and bacterial pathogenicity. We delve into the sophisticated signaling network of plants, highlighting the pivotal role of pattern recognition receptors (PRRs) in detecting conserved molecular patterns known as microbe-associated molecular patterns (MAMPs), with a particular focus on flagellin as a key MAMP. Additionally, we explore recent discoveries of solanaceous-specific receptors, such as FLAGELLIN SENSING 3 (FLS3), and their implications for plant defense responses. Furthermore, we examine the role of bacterial motility in host colonization and infection, emphasizing the multifaceted relationship between flagella-mediated chemotaxis and bacterial virulence. Through a comprehensive analysis of flagellin polymorphisms within the genus Xanthomonas, we elucidate their potential impact on host recognition and bacterial pathogenicity, offering insights into strategies for developing disease-resistant crops. This review is intended for professionals within the fields of crops sciences and microbiology.

Keywords: Flagella; Motility; Pathology; Xanthomonas.

Figure 1. Plant-associated bacteria employ various strategies to counteract pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) initiated by flagellin detection in plants.

Plants identify bacteria by recognizing conserved molecular patterns, such as peptides derived from the flagellin protein. This recognition is facilitated by the receptors FLS2 or FLS3, along with the coreceptor BAK1, which forms a complex with the flagellin-derived elicitor peptides. The polymorphism in flagella enables bacteria to evade detection or diminish the effectiveness of plant immune responses. However, plants can counter this by evolving receptor variants that are capable of recognizing these new flagellar polymorphisms, thereby restoring their ability to detect and respond to bacterial invaders. In addition to flagella, bacteria employ sophisticated secretion systems, such as the Type II Secretion System (T2SS) and Type III Secretion System (T3SS), to deliver effectors to fight plant cells. These effectors can suppress plant immunity or manipulate host cell processes to favor infection. However, plants have evolved to detect these effectors through specialized resistance proteins, which trigger strong immune responses that halt bacterial proliferation and infection. This ongoing molecular arms race between bacterial effectors and plant defenses underscores the complexity of plant-microbe interactions. Created with BioRender.com.