Plants cannot move to escape environmental challenges. Biotic stresses result from a battery of potential pathogens: fungi, bacteria, nematodes and insects intercept the photosynthate produced by plants, and viruses use replication machinery at the host's expense. Plants, in turn, have evolved sophisticated mechanisms to perceive such attacks, and to translate that perception into an adaptive response. Here, we review the current knowledge of recognition-dependent disease resistance in plants. We include a few crucial concepts to compare and contrast plant innate immunity with that more commonly associated with animals. There are appreciable differences, but also surprising parallels.

Plant pathogens and integrated defence responses to infection.

Rapid generation of superoxide and accumulation of H2O2 is a characteristic early feature of the hypersensitive response following perception of pathogen avirulence signals. Emerging data indicate that the oxidative burst reflects activation of a membrane-bound NADPH oxidase closely resembling that operating in activated neutrophils. The oxidants are not only direct protective agents, but H2O2 also functions as a substrate for oxidative cross-linking in the cell wall, as a threshold trigger for hypersensitive cell death, and as a diffusible signal for induction of cellular protectant genes in surrounding cells. Activation of the oxidative burst is a central component of a highly amplified and integrated signal system, also involving salicylic acid and perturbations of cytosolic Ca2+, which underlies the expression of disease-resistance mechanisms.

The oxidative burst in plant disease resistance

Microbe-associated molecular patterns (MAMPs) are molecular signatures typical of whole classes of microbes, and their recognition plays a key role in innate immunity. Endogenous elicitors are similarly recognized as damage-associated molecular patterns (DAMPs). This review focuses on the diversity of MAMPs/DAMPs and on progress to identify the corresponding pattern recognition receptors (PRRs) in plants. The two best-characterized MAMP/PRR pairs, flagellin/FLS2 and EF-Tu/EFR, are discussed in detail and put into a phylogenetic perspective. Both FLS2 and EFR are leucine-rich repeat receptor kinases (LRR-RKs). Upon treatment with flagellin, FLS2 forms a heteromeric complex with BAK1, an LRR-RK that also acts as coreceptor for the brassinolide receptor BRI1. The importance of MAMP/PRR signaling for plant immunity is highlighted by the finding that plant pathogens use effectors to inhibit PRR complexes or downstream signaling events. Current evidence indicates that MAMPs, DAMPs, and effectors are all perceived as danger signals and induce a stereotypic defense response.

A Renaissance of Elicitors: Perception of Microbe-Associated Molecular Patterns and Danger Signals by Pattern-Recognition Receptors

Host-microbe interactions: Shaping the evolution of the plant immune response

FLS2: an LRR receptor-like kinase involved in the perception of the bacterial elicitor flagellin in Arabidopsis.

The rice Xa21 gene, which confers resistance to Xanthomonas oryzae pv. oryzae race 6, was isolated by positional cloning. Fifty transgenic rice plants carrying the cloned Xa21 gene display high levels of resistance to the pathogen. The sequence of the predicted protein, which carries both a leucine-rich repeat motif and a serine-threonine kinase-like domain, suggests a role in cell surface recognition of a pathogen ligand and subsequent activation of an intracellular defense response. Characterization of Xa21 should facilitate understanding of plant disease resistance and lead to engineered resistance in rice.

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A receptor kinase-like protein encoded by the rice disease resistance gene, Xa21. - eScholarship

OBJECTIVE
The current research was designed to assess the efficacy of clonidine in the treatment of children with tic disorder co-morbid with attention deficit hyperactivity disorder.


PATIENTS AND METHODS
A total of 154 children with tic disorder co-morbid with attention deficit hyperactivity disorder admitted to our hospital from July 2019 to July 2022 were recruited and assigned to receive either methylphenidate hydrochloride plus haloperidol (observation group) or clonidine (experimental group), with 77 cases in each group. Outcome measures included clinical efficacy, Yale Global Tic Severity Scale (YGTSS) scores, Conners Parent Symptom Questionnaire (PSQ) scores, and adverse events.


RESULTS
Clonidine was associated with markedly higher clinical efficacy vs. methylphenidate hydrochloride plus haloperidol (p<0.05). Clonidine offered more significant mitigation of the tic disorder vs. methylphenidate hydrochloride plus haloperidol, as evinced by the lower kinetic tic scores, vocal tic scores, and total scores (p<0.05). Children exhibited markedly milder tic symptoms after clonidine monotherapy vs. those with dual therapy of methylphenidate hydrochloride and haloperidol, suggested by the lower scores of character problems, learning problems, psychosomatic disorders, hyperactivity/impulsivity, anxiety index, and hyperactivity index (p<0.05). Clonidine features a higher safety profile than methylphenidate hydrochloride plus haloperidol by reducing the incidence of adverse events (p<0.05).


CONCLUSIONS
Clonidine effectively alleviates tic symptoms, reduces attention deficit and hyperactivity/impulsivity in children with tic disorder co-morbid attention deficit hyperactivity disorder, and features a high safety profile.

G L Wang

Papers

A receptor kinase-like protein encoded by the rice disease resistance gene, Xa21. - eScholarship

Efficacy of clonidine in the treatment of children with tic disorder co-morbid with attention deficit hyperactivity disorder.