plant pathogen

Deep research

Generated by just research-trait; source: research/traits/ecology/plant_pathogen-deep-research-falcon.md

# Curation report: microbial **plant pathogen** trait

## 1. Scope summary

**Target trait:** `METPO:1004003`  
**Label:** plant pathogen  
**Category:** ECOLOGY  
**Term kind:** CLASS  
**Mapping status:** REVIEWED  
**Definition:** “A pathogen that infects organisms in the kingdom Viridiplantae.”  
**Parent:** `METPO:1004000`

### Recommended interpretation

`METPO:1004003` should represent an **organism-level, host- and context-dependent capacity to enter or colonize a Viridiplantae host, overcome or exploit host defenses, multiply in planta, and produce disease or transmissible infection**. It is not equivalent to possession of any single virulence gene. Plant pathogenicity is normally realized through a sequence of modules—environmental sensing, surface survival, entry, adhesion, nutrient acquisition, immune manipulation, tissue damage, multiplication, and dissemination—whose relative importance differs among bacterial, fungal, oomycete, phytoplasma, and protist pathogens.

The current 13-node T3SS-effector graph captures a major **bacterial hemibiotroph** mechanism, but it is not an adequate universal definition. Hrp T3SSs inject many effectors and are central in numerous Gram-negative bacterial phytopathogens, whereas fungal and oomycete pathogens commonly use secreted effectors and specialized penetration or feeding structures. Even within bacteria, soft-rot pathogens can depend more strongly on type II-secreted plant-cell-wall-degrading enzymes than on the canonical T3SS program. (o’malley2021regulationofthe pages 1-2, pfeilmeier2016bacterialpathogenesisof pages 7-8, santosbriones2024algorithmsforeffector pages 2-4, leivamora2024uncoveringthemechanisms pages 2-4)

### Boundary cases

* **Commensal, epiphytic, rhizosphere, and endophytic colonizers are not plant pathogens** unless there is evidence of disease-producing infection under an appropriate host and environment.
* **Virulence is not identical to pathogenicity.** Pathogenicity is the qualitative capacity to cause disease; virulence is its degree in a specified host, genotype, inoculum, environment, and assay.
* **Avirulence effectors are context-dependent.** An effector may promote susceptibility in one host but trigger resistance and hypersensitive cell death when recognized by the corresponding plant immune receptor.
* **Presence of a T3SS, T6SS, effector-like sequence, cell-wall-degrading enzyme, flagellum, siderophore, or biofilm locus is insufficient by itself.** These systems also occur in nonpathogenic plant-associated microbes.
* **Direct infiltration bypasses natural entry.** Flagellar mutants of *Pseudomonas syringae* and *Ralstonia solanacearum* are impaired following inoculation onto intact surfaces but not necessarily after direct infiltration; therefore, such results support an entry-stage edge rather than a universal intracellular virulence edge. (pfeilmeier2016bacterialpathogenesisof pages 7-8)
* **Latent or opportunistic disease requires metadata.** Host species and genotype, tissue, developmental state, inoculation route, dose, temperature, humidity, wounding, and disease endpoint should accompany evidence.
* **“Plant pathogen” should be assigned to the microbial entity, not to an isolated protein.** Proteins and pathways are mechanistic contributors to the terminal trait.

## 2. Current mechanistic model

A defensible cross-taxon causal architecture is:

**plant/environmental cues → virulence-program activation → access and attachment → host-barrier penetration → effector/toxin/enzyme deployment → defense suppression or tissue damage → in-planta multiplication and spread → `METPO:1004003`**.

In *P. syringae*, low nitrogen-to-carbon conditions, acidic pH, and plant-derived metabolites induce the Hrp program. Citric acid, aspartate, glutamate, and fructose-associated signals can strongly induce T3SS genes; plant signals produced approximately tenfold enhancement in the reviewed experiments. The AauSR two-component system and AatQMP transporter connect acidic-amino-acid perception to Hrp regulation. These observations are strong but species- and assay-specific. (o’malley2021regulationofthe pages 5-6, o’malley2021regulationofthe pages 15-17)

The Hrp injectisome then delivers effectors into the plant cytosol. A reviewed *P. syringae* system delivers more than 20 effectors, which collectively inhibit immune signaling or disrupt cell-surface immune-receptor functions. HrpRS and the alternative sigma factor HrpL are major regulatory nodes. (o’malley2021regulationofthe pages 1-2)

## 3. Candidate nodes grouped by type

### A. Trait and host-context nodes

| Candidate node | Type | Suggested grounding | Curation note |
|---|---|---|---|
| plant pathogen | Trait class | `METPO:1004003` | Terminal trait; quote identifier verbatim in YAML. |
| Viridiplantae host | Taxon/context | `NCBITaxon:33090` | Verify that TraitMech accepts host-taxon nodes before use. |
| intact plant surface | Environment/anatomical context | Label only | Important for natural-entry assays. |
| plant apoplast | Cellular/extracellular compartment | GO label candidate; identifier should be ontology-validated | Principal niche for many bacterial phytopathogens. |
| xylem | Plant anatomical niche | Plant Ontology candidate; validate identifier | Relevant to vascular pathogens such as *Ralstonia* and *Xanthomonas* lineages. |
| acidic, nutrient-limited plant environment | Experimental/environmental factor | Label only | Do not model as universally required. |

### B. Regulatory and sensory modules

* Plant-derived citric acid, aspartate, glutamate, fructose, and related host metabolites.
* AauSR two-component system; AatQMP ABC transporter.
* HrpRS–HrpL regulatory cascade.
* Cyclic di-GMP: a context-dependent switch inversely coordinating T3SS expression and flagellar motility in the reviewed *P. syringae* systems. (o’malley2021regulationofthe pages 15-17)
* Quorum sensing, diffusible signal factor signaling, and quorum quenching should remain **taxon-specific extension nodes** until direct phytopathogen evidence is attached; generic pathogen or biofilm reviews are not adequate evidence for `METPO:1004003`.

### C. Access, attachment, and infection structures

Showing the first 60 of 236 lines of findings; the linked file also carries the run's front matter and the prompt it was given — read the full report.