THE PLANT’S INTERNAL CELLULAR SENSING AND RESPONSE MEASURES TO MECHANICAL BREACH

Project Information

PREENER

Grant agreement ID: 101066035

DOI

10.3030/101066035

Project closed

EC signature date 28 June 2022

Start date 1 January 2023

End date 30 April 2025

Funded under

• Marie Skłodowska-Curie Actions (MSCA)

Total cost

No data

EU contribution

€ 222 727,68

Coordinated by

SVERIGES LANTBRUKSUNIVERSITET
Sweden

Periodic Reporting for period 1 - PREENER (THE PLANT’S INTERNAL CELLULAR SENSING AND RESPONSE MEASURES TO MECHANICAL BREACH)

Reporting period: 2023-01-01 to 2025-04-30

Summary of the context and overall objectives of the project

Plant-parasitic nematodes are among the most damaging plant pathogens, causing more than US$150 billion in global crop losses each year. The major losses are incurred by sedentary endoparasites consisting of root knot (Meloidogynae spp.) and cyst nematodes (Globodera spp. and Heterodera spp.). Cyst nematodes enter in the host root near elongation zone, migrate upward intra-cellularly and develop permanent feeding site inside the nutrient-rich vasculature. During their migration they pass through several cell files and leaving a trail of dead cells. On the other hand, plants, as sessile organisms, have evolved sophisticated mechanisms to navigate the complex landscape of environmental challenges. Among the myriads of stressors, cell injury emerges as a pivotal trigger, requires setting in motion a delicate interplay between two fundamental responses: regeneration and defense. When confronted with cellular damage, plants orchestrate a dynamic symphony of molecular events, activation of molecular pathways that facilitate regeneration to repair the wounded tissues and simultaneously initiate defense responses to thwart potential pathogenic invaders.

The overall objective of the current project was to elucidate these complex cell-specific responses of the host plant when encountered mechanical injuries by nematodes. It would assist in devising smart, time-driven and spatially temporal strategies to develop host resistance against parasitic nematodes in enhancing sustainable agricultural production.

The plant cell wall acts as the foremost physical barrier against plant pathogens therefore, they have evolved mechanisms to perceive and respond to any chemical, mechanical or hydraulic changes threatening cell wall integrity. The cell wall consists of cellulose, hemicellulose, pectin and lignin polymer. In Arabidopsis, lignin is mainly deposited in casparian strip of endodermal cells and secondary cell wall of vascular tissues and provides rigidity and strength against hydraulic pressure in xylem vessels. Accordingly, this study investigated lignin deposition as a defense response in mechanically injured roots, mapped tissue-specific lignin reinforcement of the cell wall, and identified transcriptional regulators involved in lignin biosynthesis. Ultimately, these mechanisms will be evaluated as avenues to strengthen plant resistance to nematode infections.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

To deliver on the aims above, we applied a multidisciplinary approach combining multiphoton single-cell ablation, laser-scanning confocal imaging, promoter–reporter lines with nuclear-localized fluorescent markers, RNA-seq, pyrolysis–GC–MS, and transmission electron microscopy (TEM).
We discovered, when plant roots are attacked by cyst nematodes, they rapidly induce localized ectopic lignin deposition as a defense mechanism. To disentangle the mechanical component of this response from pathogen-derived signals, we mimicked nematode-induced mechanical injury using highly precise multiphoton laser ablation. This revealed that ectopic lignin deposition is a cell-specific phenomenon, occurring in adjacent cells within ~ 10 hours of injury.
Reporter analyses revealed coordinated induction of the phenylpropanoid pathway that drives lignin biosynthesis after mechanical damage. In Arabidopsis roots, endodermal cells surrounding the vascular cylinder were the most responsive, while the epidermis (outermost layer) showed minimal activation. Pyrolysis-GC-MS analysis further demonstrated that the composition of ectopically induced lignin differs from that in undamaged tissues, consistent with enhanced resistance to pathogens. RNAseq analysis identified several MYB transcription factors potentially regulating lignin biosynthesis during mechanical damage. We focused on one transcription factor, MYB15 for functional characterisation using promoter–reporter lines, knockout mutants, and overexpression lines. Nematode infection assays confirmed that overexpression lines displayed increased resistance, as supported by phenotypic assessments and ultrastructural TEM analysis.
Overall, we provide a high-resolution, spatiotemporal map of injury-induced lignification in roots. The response is strongest in the endodermis (and cortex), while cells of the vascular cylinder remain available for secondary growth, allowing plants to fortify tissues against nematodes without sacrificing developmental capacity. These insights point to tractable regulatory nodes for engineering durable, tissue-targeted resistance.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Plant roots face constant challenges while growing through rough soil particles and invasive pests like nematodes. Nematodes are particularly damaging because they pierce root cells and travel deep inside to reach the plant’s nutrient-rich vascular tissue. To protect themselves, plants start a series of defense responses including reinforcing their cell walls with lignin, a tough material. Before this work, lignification during nematode infection was generally thought to be triggered mainly by pathogen-associated molecular patterns (PAMPs/NAMPs). Our study changes this view by demonstrating, with high spatial and temporal precision, that purely mechanical injury such as that caused during early cyst nematode migration is sufficient to trigger localized lignification in plant roots. This finding establishes that the plant’s early defense response against nematodes is not solely dependent on pathogen-derived signals but is also driven by the physical damage they inflict.
Another key advance from our work addresses a long-standing gap in understanding how plants distinguish routine mechanical disturbances from soil texture versus invasive penetration by pathogens. Through tissue-specific analyses combined with highly precise single-cell laser ablation and high-resolution confocal microscopy, we discovered that plants mount a much stronger lignification response when internal cell layers such as the endodermis are breached. This acts as a signal to the plant that an invasive pest has penetrated deeply. In contrast, damage limited to the outer epidermal layer, as may occur during normal root growth through the soil texture, induces almost no lignin response.
• The study provides direct experimental proof that mechanical injury alone can trigger lignification in plant roots, independent of nematode associated molecular pattrens.
• It reveals a tissue-specific damage recognition system in roots, where deeper tissue breaches elicit stronger defense responses.
• Combining laser ablation, promoter–reporter imaging, and confocal microscopy assisted in achieving unprecedented resolution in studying plant defense activation.
Overall, these findings redefine the triggers and regulation of lignification in plant–nematode interactions and open new opportunities to enhance crop resistance by strengthening their ability to rapidly detect and respond to physical invasion.