# Salicylic acid reduces MdPUB24-mediated ubiquitination of MdWRKY40 to suppress ethylene biosynthesis in apple fruit

## TL;DR

Salicylic acid suppresses ethylene production in apples by reducing the breakdown of a protein that inhibits ripening.

## Contribution

The study reveals a novel regulatory mechanism involving MdPUB24 and MdWRKY40 in SA-mediated ethylene suppression during apple ripening.

## Key findings

- MdWRKY40 represses ethylene biosynthesis by inhibiting MdACS1 gene expression.
- MdPUB24 ubiquitinates and degrades MdWRKY40, a process suppressed by salicylic acid.
- The MdPUB24-MdWRKY40-MdACS1 module mediates SA's effect on ethylene suppression in apple fruit.

## Abstract

The plant hormone salicylic acid (SA) effectively suppresses ethylene biosynthesis in apple (Malus domestica) fruit. However, the underlying molecular mechanism remains unclear. Here, we identified a WRKY transcription factor, MdWRKY40, which was upregulated in response to SA treatment. MdWRKY40 functioned as a transcriptional repressor of the ethylene biosynthesis gene MdACS1 (1-aminocyclopropane-1-carboxylic acid synthase 1). In addition, we found that the expression of U-box-type E3 ubiquitin ligase MdPUB24 was downregulated following SA treatment. MdPUB24 interacted with MdWRKY40 and mediated its ubiquitination, leading to the degradation of MdWRKY40 via the 26S proteasome pathway, which was suppressed by SA. Together, these results suggest that the MdPUB24-MdWRKY40-MdACS1 regulatory module mediates SA-induced suppression of ethylene biosynthesis by post-translational modification during apple fruit ripening. These findings offer new insights into the molecular basis of fruit ripening inhibition and shelf-life extension.