A novel MLO protein CsMLO4 plays an essential role in cucumber resistance to target leaf spot

Abstract

Target leaf spot (TLS), caused by Corynespora cassiicola, is a prevalent leaf disease that significantly impacts cucumber yield and quality. Breeding disease-resistant cucumber varieties is a key strategy for managing this disease, and identifying critical resistance genes is essential for genetic improvement. In this study, we identified a highly susceptible mutant to TLS in the Tnt1 retrotransposon mutant library. Bulked segregation analysis sequencing (BSA-seq) further pinpointed a candidate gene for TLS resistance, encoding the Mildew Resistance Locus O (MLO) protein, CsMLO4. Expression analysis revealed that CsMLO4 is strongly induced by C. cassiicola infection. Functional analyses revealed that loss of function and silencing of CsMLO4 attenuated resistance to TLS and exhibited reduced reactive oxygen species (ROS) accumulation, while transient overexpression of CsMLO4 enhanced both disease resistance and ROS levels. These findings suggest that CsMLO4 mediates cucumber defense against C. cassiicola by modulating ROS levels. Additionally, transcriptome analysis identified multiple disease-resistance-related pathways affected by the loss of function of CsMLO4. Overexpression of CsMYB, a potential candidate gene regulated by CsMLO4, showed enhanced resistance to C. cassiicola. This study expands insights into the functional role of MLO family beyond their association with powdery mildew resistance and offers new perspectives on the mechanisms underlying TLS resistance in cucumber.

Acknowledgements

This work was supported by the Liaoning Provincial Department of Education Innovation Team Project (grant number JYTTD2024005).

Author contributions

H.F. and J.P. provided ideas and guided this study. Y.Y. and J.H. conducted experiments. X.M. analyzed the data. Y.Y. wrote the manuscript. J.P. revised the manuscript. Y.J., J.H., Y.Y., N.C., and R.C. helped with the experiment. All authors agreed to the manuscript.

Data availability

The data underlying this article are available in the article and in its online supplementary material.

Conflict of interest statement

The authors declare no conflict of interest.

Supplementary data

Supplementary data is available at Horticulture Research online.

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