Protection Against Common Bean Rust Conferred by a Gene-Silencing Method

Area of Science:

• Plant Pathology
• Molecular Biology
• Mycology

Background:

• Rust disease in dry beans (Phaseolus vulgaris) is caused by the fungus Uromyces appendiculatus.
• The fungus utilizes haustoria to secrete effector proteins, suppressing the plant's immune system for pathogenicity.
• Identifying these effector proteins is crucial for understanding and combating the disease.

Purpose of the Study:

• To investigate the role of Uromyces appendiculatus effector proteins in rust pathogenicity.
• To explore the potential of using RNA interference (RNAi) delivered from the plant to the fungus to control rust disease.

Main Methods:

• Candidate effector genes were identified through DNA sequencing and motif analysis.
• Fragments of candidate effector genes were inserted into Bean pod mottle virus (BPMV) for expression in infected plants.
• Plants infected with recombinant BPMV were challenged with U. appendiculatus to assess disease severity.

Main Results:

• Plants expressing gene fragments for four out of five candidate effectors showed significantly reduced rust accumulation and disease severity.
• Control plants expressing a non-haustorial fungal gene fragment exhibited a synergistic reaction between BPMV and U. appendiculatus, leading to plant death.
• Evidence suggests that plant-generated RNA moved into the fungus via haustoria to silence effector genes.

Conclusions:

• Four Uromyces appendiculatus genes encode crucial pathogenicity determinants.
• Expression of fungal RNA within the plant host can effectively silence fungal effector genes.
• This study demonstrates a novel RNAi-based strategy for protecting dry bean plants against rust disease.