Domestication-Selected Promoter Insertion in WRKY17 Increases Cadmium Sensitivity in Apple

Area of Science:

• Plant Genetics
• Environmental Science
• Molecular Biology

Background:

• Heavy metal pollution, especially cadmium (Cd), poses a significant environmental threat due to industrialization.
• Differential tolerance to Cd exists between wild apple (Malus spp.) and cultivated apple (Malus domestica).

Purpose of the Study:

• To identify the genetic basis for differential cadmium tolerance in apples.
• To elucidate the molecular mechanism underlying cadmium stress response regulation by WRKY17.
• To explore practical strategies for mitigating cadmium contamination in apple cultivation.

Main Methods:

• Pan-genome analysis to identify key genetic regulators.
• Gene expression analysis of WRKY17 and related genes under cadmium stress.
• Molecular mechanism studies involving long non-coding RNA (lncRNA400) and epigenetic modifications (H3K27me3).
• Grafting experiments to assess practical applications.

Main Results:

• A 3355-bp insertion (P-INS) in the WRKY17 promoter region is the primary genetic determinant of differential Cd tolerance.
• P-INS suppresses WRKY17 expression in cultivated apples, reducing Cd tolerance, while its absence in wild apples leads to activated WRKY17 expression.
• WRKY17 enhances Cd tolerance by inducing lncRNA400, which recruits JMJD5 to activate the Plant Cadmium Resistance gene PCR2.
• WRKY17 activation accelerates leaf senescence, explaining P-INS retention during domestication for agronomic traits.
• Grafting wild apple rootstocks with cultivated scions combines Cd tolerance and desirable agronomic traits.

Conclusions:

• WRKY17, regulated by P-INS, is a crucial factor in apple cadmium tolerance.
• The molecular pathway involving WRKY17, lncRNA400, JMJD5, and PCR2 mediates cadmium resistance.
• Grafting offers a viable strategy for developing cadmium-resistant apple cultivars with improved agronomic characteristics.