Abstract
Autophagy is a well-defined catabolic mechanism whereby cytoplasmic materials are engulfed into a structure termed the autophagosome. Methyl jasmonate (MeJA), a plant hormone, mediates diverse developmental process and defense responses which induce a variety of metabolites. In plants, little is known about autophagy-mediated responses against MeJA. In this study, we used high-throughput comparative proteomics to identify proteins of latex in the laticifers. The isobaric tags for relative and absolute quantification (iTRAQ) MS/MS proteomics were performed, and 298 proteins among MeJA treated groups and the control group of Euphorbia kansui were identified. It is interesting to note that 29 significant differentially expressed proteins were identified and their associations with autophagy and ROS pathway were verified for several selected proteins as follows: α-L-fucosidase, β-galactosidase, cysteine proteinase, and Cu/Zn superoxide dismutase. Quantitative real-time PCR analysis of the selected genes confirmed the fact that MeJA might enhance the expression of some genes related to autophagy. The western blotting and immunofluorescence results of ATG8 and ATG18a which are two important proteins for the formation of autophagosomes also demonstrated that MeJA could promote autophagy at the protein level. Using the electron microscope, we observed an increase in autophagosomes after MeJA treatment. These results indicated that MeJA might promote autophagy in E. kansui laticifers; and it was speculated that MeJA mediated autophagy through two possible ways: the increase of ROS induces ATG8 accumulation and then aotophagosome formation, and MeJA promotes ATG18 accumulation and then autophagosome formation. Taken together, our results provide several novel insights for understanding the mechanism between autophagy and MeJA treatment. However, the specific mechanism remains to be further studied in the future.
Highlights
Jasmonate (JA) and its volatile form, methyl jasmonate (MeJA) are collectively called jasmonates (JAs)
Combining the de novo annotation of E. kansui transcriptomic data with isobaric tags for relative and absolute quantification (iTRAQ) analysis; and on the basis of gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, we identified some proteins showing significant differences were related to ROS pathway and autophagy
We observed the ultrastructural changes of E. kansui laticifers treated with MeJA. These results reveal that MeJA promote the autophagy in E. kansui laticifers
Summary
Jasmonate (JA) and its volatile form, methyl jasmonate (MeJA) are collectively called jasmonates (JAs). As a type of plant hormones, JAs involved in regulating diverse development processes (fertility, seed germination, root growth, and fruit ripening) and defense responses to abiotic (drought, low temperature, and salinity) and biotic stresses (insect-driven wounding and various pathogens) [1,2,3]. MeJA promotes the transcription and expression of the vegetative storage protein (VSP) in Medicago sativa [11], and induces the biosynthesis of secondary plant metabolites. It has been reported that exogenous JAs can stimulate formation and differentiation of laticifers, a specific type of cell, in Hevea brasiliensis, and they can induce the production of numerous secondary metabolities, including latex [11,12]
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