Pathogen-Associated Molecular Pattern-Triggered Immunity Involves Proteolytic Degradation of Core Nonsense-Mediated...

Area of Science:

• Plant molecular biology
• Plant immunity
• mRNA regulation

Background:

• Nonsense-mediated mRNA decay (NMD) is a crucial mRNA quality control pathway.
• NMD is implicated in plant immune responses, but its precise role remains unclear.
• Certain resistance (R) gene transcripts increase during bacterial infections in Arabidopsis.

Purpose of the Study:

• To investigate the role of NMD in regulating R gene expression during plant-bacterial interactions.
• To elucidate the molecular mechanisms by which NMD factors are regulated during early plant immune responses.

Main Methods:

• Analysis of transcript levels of fully spliced (FS) transcripts from TIR-NBS-LRR and CC-NBS-LRR genes.
• Investigating the degradation of core NMD factors (UPF1, UPF2, UPF3) upon bacterial inoculation.
• Utilizing Arabidopsis mutants (mpk3, mpk6, salicylic acid signaling, upf mutants) to dissect signaling pathways.
• Assessing disease resistance in upf mutants challenged with Pseudomonas.

Main Results:

• A significant proportion of FS TNL and CC-NBS-LRR transcripts exhibit NMD regulation.
• Bacterial infection and pattern recognition receptor (PRR) perception rapidly induce UPF1, UPF2, and UPF3 degradation via ubiquitination and proteasomal pathways.
• UPF1 and UPF3 ubiquitination are delayed in mpk3 and mpk6 mutants, indicating a role for these kinases.
• Accumulation of uncharacterized TNL-type R transcripts in upf mutants confers enhanced resistance to virulent Pseudomonas.

Conclusions:

• NMD is a key post-transcriptional regulatory mechanism controlling R gene expression in Arabidopsis immunity.
• PRRs fine-tune R transcript levels through NMD to balance fitness costs and effective immunity.
• The study reveals a novel mechanism linking NMD, MAPK signaling, and plant defense.