The phloem lectin PP2-A1 enhances aphid resistance by affecting aphid behavior and maintaining ROS homeostasis in cucumber plants

Aphid (Aphis gossypii Glover) attack frequently results in a significant loss of output and deterioration of fruit quality in cucumber (Cucumis sativus L.). Phloem protein 2 (PP2) is conserved as a phloem lectin in plants, and few studies have been conducted on the regulatory mechanism of PP2. Based on our previous study of CsPP2-A1 in cucumber, to further investigate the biological function of CsPP2-A1, we compared the changes of selectivity, non-selectivity, colonization, reproductions of aphids, and the phenotype in wild type (WT), CsPP2-A1 over -expressing (CsPP2-A1-OE), and CsPP2-A1 interfering (CsPP2-A1-RNAi) cucumber plants after inoculation with aphids. We found that CsPP2-A1-OE cucumber plants generated resistance to aphids. The aphid colonization rate and number of reproductions of CsPP2-A1-OE cucumber plants were significantly lower than that of WT and CsPP2-A1-RNAi cucumber plants. Through Pearson's correlation and principal component analysis (PCA), it was found that CsPP2-A1 played a crucial role in the balance of reactive oxygen species (ROS) in plants. Over -expression of the CsPP2-A1 resulted in increased levels of antioxidant enzyme, eliminating ROS and preventing the damage by ROS in cucumber. Furthermore, nutritional imbalance for aphids and content of secondary me-tabolites were increased in overexpressed CsPP2-A1 cucumber plants, and thus preventing aphid attack. These together may improve cucumber resistance against aphids and the mechanism of CsPP2-A1 defense against aphids was preliminarily explored.

Automated summary

Aphid attack often leads to decreased yields and deteriorated fruit quality in cucumber. The overexpression of CsPP2-A1 in cucumber plants resulted in resistance against aphids, with significantly lower colonization rates and reproductions compared to wild type and CsPP2-A1-RNAi plants. CsPP2-A1 played a crucial role in balancing reactive oxygen species (ROS) in plants, and its overexpression increased antioxidant enzyme levels, eliminating ROS and preventing their damage in cucumber. Furthermore, the overexpressed CsPP2-A1 cucumber plants showed nutritional imbalance for aphids and increased content of secondary metabolites, thereby preventing aphid attack.