Clade V MLO Genes Are Negative Modulators of Cucumber Defence Response to Meloidogyne incognita

Abstract

Cucumber production is seriously constrained by Meloidogyne incognita. Because no resistance resources to the pathogen have been reported, disabling susceptibility genes may represent a novel breeding strategy to introduce resistance against this nematode in cucumber. Here, we studied the clade V MLO genes for their involvement in the interaction between cucumber and M. incognita. Our results showed that Arabidopsis clade V MLO mutants were resistant to M. incognita. Cucumber has three clade V MLO genes, CsaMLO1, CsaMLO8 and CsaMLO11, with upregulated expression upon inoculation with M. incognita. Heterologous overexpression of CsaMLO1, CsaMLO8 and CsaMLO11 in Arabidopsis mutants restored susceptibility to varying degrees. Silencing and knockout of individual clade V MLO genes in cucumber reduced susceptibility to M. incognita. The cucumber CRISPR mutants produced similar fruits as the wild type (WT) did. Although the yields of two single mutants (M111 and M112) and two double mutants (M81 M111 and M81 M112) were reduced compared to WT, the yields of M81 and M82 were not decreased. In summary, clade V MLO genes function as susceptibility genes for M. incognita in cucumber. Among them, CsaMLO8 may be the most promising candidate for M. incognita resistance breeding in cucumber.