ERF4 affects fruit firmness through TPL4 by reducing ethylene production

Area of Science:

• Plant Molecular Biology
• Fruit Genetics
• Agricultural Science

Background:

• Fruit firmness is crucial for crop quality, consumer appeal, and post-harvest life.
• Ethylene signaling pathways play a significant role in fruit ripening and texture development.

Purpose of the Study:

• To investigate the genetic basis of apple fruit texture, specifically focusing on the ETHYLENE RESPONSE FACTOR4 (ERF4) gene.
• To elucidate the molecular mechanism by which ERF4 influences fruit firmness and ethylene biosynthesis.

Main Methods:

• Combined quantitative trait locus (QTL) and genome-wide association studies (GWAS) in apple.
• Chromatin immunoprecipitation sequencing (ChIP-seq) to identify ERF4 binding targets.
• Biolayer interferometry to assess protein-protein interactions.

Main Results:

• A C-G mutation in the ethylene response factor-associated amphiphilic repression (EAR) motif of ERF4 was identified, affecting apple fruit texture.
• ERF4 directly binds to the promoter of ERF3, a gene involved in ethylene biosynthesis regulation.
• The EAR motif mutation in ERF4 reduces its repression of ERF3, leading to increased ethylene production and decreased fruit firmness.
• ERF4's repressive activity is mediated by interaction with TOPLESS co-repressor 4 (TPL4); the mutation impairs this interaction.
• Suppression of ERF4 or TPL4 accelerates fruit ripening and ethylene production.

Conclusions:

• Allelic variation in the apple ERF4 gene, specifically within the EAR motif, is a key determinant of fruit firmness.
• The ERF4-TPL4 interaction is critical for regulating ERF3 expression and, consequently, ethylene production and fruit ripening.
• Understanding this mechanism provides insights into breeding strategies for improved fruit quality traits.