Enhanced resistance to citrus canker in transgenic mandarin expressing Xa21 from rice

AbstractXyloglucans are highly substituted and recalcitrant polysaccharides found in the primary cell walls of vascular plants, acting as a barrier against pathogens. Here, we reveal that the diverse and economically relevant Xanthomonas bacteria are endowed with a xyloglucan depolymerization machinery that is linked to pathogenesis. Using the citrus canker pathogen as a model organism, we show that this system encompasses distinctive glycoside hydrolases, a modular xyloglucan acetylesterase and specific membrane transporters, demonstrating that plant-associated bacteria employ distinct molecular strategies from commensal gut bacteria to cope with xyloglucans. Notably, the sugars released by this system elicit the expression of several key virulence factors, including the type III secretion system, a membrane-embedded apparatus to deliver effector proteins into the host cells. Together, these findings shed light on the molecular mechanisms underpinning the intricate enzymatic machinery of Xanthomonas to depolymerize xyloglucans and uncover a role for this system in signaling pathways driving pathogenesis.

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A family of pathogen-induced cysteine-rich transmembrane proteins is involved in plant disease resistance

Planta ◽

10.1007/s00425-021-03606-3 ◽

2021 ◽

Vol 253 (5) ◽

Author(s):

Marciel Pereira Mendes ◽

Richard Hickman ◽

Marcel C. Van Verk ◽

Nicole M. Nieuwendijk ◽

Anja Reinstädler ◽

...

Keyword(s):

Arabidopsis Thaliana ◽

Plasma Membrane ◽

Disease Resistance ◽

Plant Disease Resistance ◽

Transmembrane Proteins ◽

Series Data ◽

Immune Gene ◽

Biological Processes ◽

Hypocotyl Growth ◽

Enhanced Resistance

Abstract Main conclusion Overexpression of pathogen-induced cysteine-rich transmembrane proteins (PCMs) in Arabidopsis thaliana enhances resistance against biotrophic pathogens and stimulates hypocotyl growth, suggesting a potential role for PCMs in connecting both biological processes. Abstract Plants possess a sophisticated immune system to protect themselves against pathogen attack. The defense hormone salicylic acid (SA) is an important player in the plant immune gene regulatory network. Using RNA-seq time series data of Arabidopsis thaliana leaves treated with SA, we identified a largely uncharacterized SA-responsive gene family of eight members that are all activated in response to various pathogens or their immune elicitors and encode small proteins with cysteine-rich transmembrane domains. Based on their nucleotide similarity and chromosomal position, the designated Pathogen-induced Cysteine-rich transMembrane protein (PCM) genes were subdivided into three subgroups consisting of PCM1-3 (subgroup I), PCM4-6 (subgroup II), and PCM7-8 (subgroup III). Of the PCM genes, only PCM4 (also known as PCC1) has previously been implicated in plant immunity. Transient expression assays in Nicotiana benthamiana indicated that most PCM proteins localize to the plasma membrane. Ectopic overexpression of the PCMs in Arabidopsis thaliana resulted in all eight cases in enhanced resistance against the biotrophic oomycete pathogen Hyaloperonospora arabidopsidis Noco2. Additionally, overexpression of PCM subgroup I genes conferred enhanced resistance to the hemi-biotrophic bacterial pathogen Pseudomonas syringae pv. tomato DC3000. The PCM-overexpression lines were found to be also affected in the expression of genes related to light signaling and development, and accordingly, PCM-overexpressing seedlings displayed elongated hypocotyl growth. These results point to a function of PCMs in both disease resistance and photomorphogenesis, connecting both biological processes, possibly via effects on membrane structure or activity of interacting proteins at the plasma membrane.

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