（1Horticultural College，Henan Agricultural University，Zhengzhou 450002，Henan，China；2 Institute of Vegetables and Flowers，Chinese Academy of Agricultural Sciences，Beijing 100081，China；3 Wageningen University，The Netherlands）
The objective of the current study was to exploit susceptible gene（S-gene）for DM in cucumber，which will be provided as target S-gene for editing and functional analysis，leading to a new way of breeding for durable and broad-spectrum resistance to DM in cucumber. A total of 15 cucumber inbred lines of different genetic background of DM resistance（DMR） was used to identify and clone the homologs of DMR6，a DM S-gene in Arabidopsis，with the analysis of systematic evolutionary tree and major QTLs of cucumber DMR. A highly homologue candidate S-gene CsaDMR6-2 was identified. The alignment of the amino acid sequences and the prediction of secondary and tertiary protein structures between CsaDMR6-2 and Arabidopsis genes DMR6，DLO1 and DLO2 of known functions indicated that one base-pair mutation was found at 856 bp of CDS sequence of CsaDMR6-2 from K15 and K58 of European type with DMR，leading to the change of amino acids from serine（TCA） into alanine（GCA），which resulted in some changes of their protein secondary and tertiary structures.The results also indicated that CsaDMR6-2 and Arabidopsis genes DMR6，DLO1 and DLO2 have very high homologue in sequences. They are in the same group of oxidases，having the same domain and the same mutation location happened in catalytic region from the DMR genotype. The current study provided support to further function analysis of CsaDMR6-2 and the utilization of S gene for durable and broad-spectrum resistance to DM in cucumber.
