Changes in the Plant β-Sitosterol/Stigmasterol Ratio Caused by the Plant Parasitic Nematode Meloidogyne incognita

Sterols play a key role in various physiological processes of plants. Commonly, stigmasterol, beta-sitosterol and campesterol represent the main plant sterols, and cholesterol is often reported as a trace sterol. Changes in plant sterols, especially in beta-sitosterol/stigmasterol levels, can be induced by different biotic and abiotic factors. Plant parasitic nematodes, such as the root-knot nematode Meloidogyne incognita, are devastating pathogens known to circumvent plant defense mechanisms. In this study, we investigated the changes in sterols of agricultural important crops, Brassica juncea (brown mustard), Cucumis sativus (cucumber), Glycine max (soybean), Solanum lycopersicum (tomato) and Zea mays (corn), 21 days post inoculation (dpi) with M. incognita. The main changes affected the beta-sitosterol/stigmasterol ratio, with an increase of beta-sitosterol and a decrease of stigmasterol in S. lycopersicum, G. max, C. sativus and Z. mays. Furthermore, cholesterol levels increased in tomato, cucumber and corn, while cholesterol levels often were below the detection limit in the respective uninfected plants. To better understand the changes in the beta-sitosterol/stigmasterol ratio, gene expression analysis was conducted in tomato cv. Moneymaker for the sterol 22C-desaturase gene CYP710A11, responsible for the conversion of beta-sitosterol to stigmasterol. Our results showed that the expression of CYP710A11 was in line with the sterol profile of tomato after M. incognita infection. Since sterols play a key role in plant-pathogen interactions, this finding opens novel insights in plant nematode interactions.