Expression and functional analysis of the propamocarb-related gene CsMAPEG in cucumber

Propamocarb (PM) is one of the main pesticides used for controlling cucumber downy mildew. However, due to its volatility and internal absorption, PM can easily form pesticide residues on cucumber fruits that seriously endanger human health and pollute the environment. The breeding of new cucumber varieties with a low abundance of PM residues via genetic methods constitutes an effective strategy for reducing pesticide residues and improving cucumber safety and quality. To help elucidate the molecular mechanism resulting in a low PM residue abundance in cucumber, we used the cucumber cultivar 'D0351' (which has the lowest PM residue content) as the test material and identified genes related to low PM residue abundance through high-throughput tag-sequencing (Tag-Seq).

CsMAPEG was constitutively expressed and showed both varietal and organizational differences. This gene was strongly expressed in 'D0351'. The expression levels of CsMAPEG in different cucumber tissues under PM stress were as follows: fruit>leaf>stem>root. CsMAPEG can respond to salicylic acid (SA), gibberellin (GA) and Corynespora cassiicola Wei (Cor) stress and thus plays an important regulatory role in plant responses to abiotic and biological stresses. The PM residue abundance in the fruits of CsMAPEG-overexpressing plants was lower than those found in antisense CsMAPEG plants and wild-type plants at all tested time points. The results revealed that CsMAPEG played a positive role in reducing the PM residue abundance. A CsMAPEG sense construct increased the contents of SOD, POD and GST in cucumber fruits, enhanced the degradation and metabolism of PM in cucumber, and thus effectively reduced the pesticide residue abundance in cucumber fruits.

The expression patterns of CsMAPEG in cucumber cultivars with high and low pesticide residue abundances and a transgenic verification analysis showed that CsMAPEG can actively respond to PM stress and effectively reduce the PM residue abundance in cucumber fruits. The results of this study will help researchers further elucidate the mechanism responsible for a low PM residue abundance in cucumber and lay a foundation for the breeding of new agricultural cucumber varieties with low pesticide residue abundances.