Proteomic profiling of proteins associated with the rejuvenation of Sequoia sempervirens (D. Don) Endl

Mass spectrometry-based proteomic analysis revealed three proteins that differentially accumulated in different rejuvenation stages, including oxygen-evolving enhancer protein 2 (OEE2), glycine-rich RNA-binding protein (RNP), and a thaumatin-like protein. OEE2 was found to be phosphorylated and a phosphopeptide (YEDNFDGNSNVSVMVpTPpTDK) was identified. Specifically, the protein levels of OEE2 increased as a result of grafting and displayed a higher abundance in plants during the juvenile and rejuvenated stages. Additionally, SsOEE2 displayed the highest expression levels in Sequoia shoots during the juvenile stage and less expression during the adult stage. The expression levels also steadily increased during grafting.Our results indicate a positive correlation between the gene and protein expression patterns of SsOEE2 and the rejuvenation process, suggesting that this gene is involved in the rejuvenation of Sequoia sempervirens.Plant maturation involves sequential developmental stages or phases that can be categorized as embryo, juvenile, transitional, and adult. The development of reproductively mature adult plants usually begins with a strictly vegetative juvenile phase. Maturation or a phase change is completed within weeks among annuals but can proceed for several years among perennials. In trees, the process is frequently accompanied by ancillary morphological and physiological traits, most commonly a loss of competence for adventitious rooting and a loss of overall vigor. Because a plant's developmental phase is determined in its shoot apical meristems, reversing the phase of the meristems should result in the emergence of rejuvenated shoots [1]. Indeed, new growths with reversed phases have been obtained by applying gibberellin [2] and cytokinin [3,4], continuously subculturing shoots, especially in cytokinin-containing media [5-7], and repeatedly grafting shoot apices from mature trees onto juvenile rootstocks in vivo [8,9] and in vitro [10-15].Sequoia sempe