The Arabidopsis miR396 mediates pathogen-associated molecular pattern-triggered immune responses against fungal pathogens

Abstract

MicroRNAs (miRNAs) play a pivotal role in regulating gene expression during plant development. Although a substantial fraction of plant miRNAs has proven responsive to pathogen infection, their role in disease resistance remains largely unknown, especially during fungal infections. In this study, we screened Arabidopsis thaliana lines in which miRNA activity has been reduced using artificial miRNA target mimics (MIM lines) for their response to fungal pathogens. Reduced activity of miR396 (MIM396 plants) was found to confer broad resistance to necrotrophic and hemibiotrophic fungal pathogens. MiR396 levels gradually decreased during fungal infection, thus, enabling its GRF (GROWTH-REGULATING FACTOR) transcription factor target genes to trigger host reprogramming. Pathogen resistance in MIM396 plants is based on a superactivation of defense responses consistent with a priming event during pathogen infection. Notably, low levels of miR396 are not translated in developmental defects in absence of pathogen challenge. Our findings support a role of miR396 in regulating plant immunity, and broaden our knowledge about the molecular players and processes that sustain defense priming. That miR396 modulates innate immunity without growth costs also suggests fine-tuning of miR396 levels as an effective biotechnological means for protection against pathogen infection.

Robust increase of leaf size by Arabidopsis thaliana GRF3-like transcription factors under different growth conditions

“…Recently, it has been shown that MIM396 plants, with low miR396 activity, develop fast and strong immune responses and increased resistance to nectrotrophic and hemibiotrophic fungi, apparently by triggering defense priming 47 . Our results suggest that At-GRF3 could mediate similar responses as well.…”

“…This contrasts with many examples illustrating the costs of increasing defenses, where activation of immune pathways under non-stress conditions produces a fruitless diversion of energy that causes a negative effect on plant growth and fitness 48 . In turn, other plants with enhanced resistance and no fitness cost have also been described, including MIM396 itself 47 and overexpressors of NPR1 49 . Then, it is expected that rGRF3 plants may achieve a suitable balance to improve both stress response and growth under adverse conditions, however, we cannot exclude that GRF3 has different roles in these processes.…”

The lre‐miR159a‐LrGAMYB pathway mediates resistance to grey mould infection in Lilium regale

“…conglutinans and Colletotrichum higginsianum. The MIM396 plant, in which miR396 activity is reduced, was more resistant to these fungal infections, whereas the overexpression of MIR396 increased plant susceptibility to fungal infections (Soto-Suárez et al, 2017). Moreover, slmiR482e-3p, which targets FRG3…”

Boosting photosynthetic machinery and defense priming with chitosan application on tomato plants infected withFusarium oxysporumf. sp.lycopersici

“…Each reaction was performed in triplicate with two biological replicates. ΔCT values were compared, as described by(Soto-Suárez et al, 2017). The sequence for all primers used in this work are found in…”