Recently, the innovation team of Cucurbitaceae Vegetable Genetics and Breeding at the Institute of Vegetables and Flowers (IVF, CAAS) made important progress in uncovering the molecular mechanism of powdery mildew (PM) resistance in cucumber. The paper was published in Horticulture Research.

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PM is one of the most destructive diseases that threaten cucumber production globally. Efficient breeding of novel PM-resistant cultivars, will require a robust understanding of the molecular mechanisms for cucumber resistance against PM. 

Using a genome wide association study (GWAS), the team detected a locus significantly correlated with PM resistance in cucumber stem, pm-s5.1. A 1,449-bp insertion in the CsMLO8 coding region at the pm-s5.1 locus results in enhanced stem PM resistance.

Molecular view

Knockout mutants of CsMLO8 and CsMLO11 generated by CRISPR/Cas9 both showed improved PM resistance in the stem, hypocotyl and leaves, and the double mutant mlo8mlo11 displayed even stronger resistance. The team found that reactive oxygen species (ROS) accumulation was higher in the stem of these mutants.

Protein interaction assays suggested that CsMLO8 and CsMLO11 could physically interact with CsRbohD and CsCRK2, respectively. Further, the team showed that CsMLO8 and CsCRK2 competitively interact with the C-terminus of CsRbohD to affect the CsCRK2-CsRbohD module-mediated ROS production during PM defense. These findings provide new insights into the understanding of CsMLO proteins during PM defense responses.

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Source: Horticulture Research

A schematic model explaining the possible mechanism of CsMLO8-triggered PM susceptibility in cucumber

This study was led by groups from IVF-CAAS, Prof. Zhang Shengping, Prof. Yang Xueyong, and Prof. Sun Jiaqiang are co-corresponding authors. Dong Shaoyun, Liu Xin, Han jianan, and Miao Han contributed equally to this work as co-first authors. This work was funded by the National Natural Science Foundation of China, Beijing Municipal Science and Technology Commission Program, the Earmarked Fund for Modern Agro-industry Technology Research System, Science and Technology Innovation Program of the Chinese Academy of Agricultural Science.

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