Abstract: 【Objective】 Bud mutation of citrus is one of the most important breeding technique for new cultivars. However, little is known about the mechanisms of citrus bud mutation, particularly at the molecular level. Mingliutianju (C. reticuiata Blanco cv. Mingliutianju, MP) is a new cultivar selected from Chuntianju (C. reticuiata Blancocv. Chuntianju, CP) bud mutation. To identify the differentially expressed proteins in peels of Chuntianju (C. reticuiata Blanco cv. Chuntianju, CP) and its bud mutant Mingliutianju (C. reticuiata Blanco cv. Mingliutianju, MP) and to clarify the possible mechanism of this phenotype bud mutation. 【Method】Two-dimensional gel electrophoresis (2-DE) combined with the mass spectrometry (MS) technology were applied to separate the differentially expressed proteins (DEPs) between the MP and CP using peels at 12 weeks and 23 weeks after flowering. Meanwhile, the identified differentially expressed proteins (DEPs) with fold-change of more than 2 were analyzed using MALDI-TOF-MS and Bioinformatics. 【Result】 Clear 2-DE gel maps of peels of both CP and MP were successfully obtained. In total, more than 1200 protein spots and 500 protein spots were detected by silver stained (SS) 2-DE gels and by Coomassie brilliant blue stained (CS) 2-DE gels respectively. Forty DEP spots (20 identified from SS 2-DE gels and 20 from CS 2-DE gels) were further analyzed through MALDI-TOF-MS. Totally, 33 annotated DEPs, including 17 up-regulated and 16 down-regulated DEPs, were identified in MP. Gene ontology analysis revealed that these 33 DEPs could be divided into 11 categories including carbohydrate/energy metabolism, stress/defense response, nucleotide metabolism, amino acid metabolism, transcription, nitrogen metabolism, lipid metabolism, unclassified, protein modification and degradation and unknown pathways. Moreover, by using the web-based platform KOBAS (KEGG Ontology-Based Annotation System), 18 of the 33 DEPs were successfully mapped to 31 KEGG pathways, among which the flavonol biosynthetic process pathway was ranked the first. 【Conclusion】 Intensive studies were conducted to identify the mechanism that lead to the morphological differences between CP and MP from both the gene expression and the protein expression levels. Results generated in this study suggested that the flavonol biosynthetic process play an essential role in CP’s spontaneous bud mutation process. Notably, the differential expression of 2 UDP-glucosyltransferase genes and 1 caffeoyl-CoA O-methyltransferase protein may contribute a lot to the morphological differences.

Key words: citrus, bud mutant, two-dimensional electrophoresis, differentially expressed proteins, MALDI-TOF/TOF-MS