Comparative proteomic analysis of latex from Euphorbia kansui laticifers at different development stages with and without UV-B treatment via iTRAQ-coupled two-dimensional liquid chromatography-MS/MS.

Euphorbia kansui Liou, an endemic species in China, is well-known in traditional Chinese medicine. All parts of E. kansui contain white latex, which is the protoplasm constituent of specialised cells known as laticifers. The latex contains many proteins with various biological functions. In the present study, isobaric tagging for relative and absolute quantitation (iTRAQ) and MS technology combined with western blot and quantitative real-time PCR analysis were used to identify latex proteins and analyse differentially accumulated proteins in laticifers at different development stages, with and without UV-B treatment according to the E. kansui transcriptome database and the NCBI Euphorbiaceae RefSeq protein database. A total of 322 latex proteins were successfully identified. Proteasome subunits, ubiquitinated proteins, vacuolar ATP synthase (V-ATPase) and lysosomal enzymes decreased, keeping the content at a higher level in laticifers in the early development stage. These results suggest that the ubiquitin-proteasome pathway and the lysosome autophagy pathway were involved in the partial degradation of laticifer cytoplasm. In addition, terpenoid biosynthesis-related proteins, 14-3-3 protein, V-ATPase and lysosomal enzymes increased under UV-B treatment, which showed that partial cytoplasmic degradation is positively correlated with secondary metabolite synthesis in the development of E. kansui laticifers. Besides, UV-B radiation can increase plant resistance by promoting laticifer development in E. kansui. This information provides a basis for further exploration of E. kansui laticifer development, and terpenoid synthesis and regulation.