Use Chou's 5-steps rule to identify protein post-translational modification and its linkage to secondary metabolism during the floral development of Lonicera japonica Thunb.

Lonicera japonica Thunb. is widely used in traditional medicine systems of East Asian and attracts a large amount of studies on the biosynthesis of its active components. Currently, there is little understanding regarding the regulatory mechanisms behind the accumulation of secondary metabolites during its developmental stages. In this study, published transcriptomic and proteomic data were mined to evaluate potential linkage between protein modification and secondary metabolism during the floral development. Stronger correlations were observed between differentially expressed genes (DEGs) and their corresponding differentially abundant proteins (DAPs) in the comparison of juvenile bud stage (JBS)/third green stage (TGS) vs. silver flowering stage (SFS). Seventy-five and 76 cor-rDEGs and cor-rDAPs (CDDs) showed opposite trends at both transcriptional and translational levels when comparing their levels at JBS and TGS relative to those at SFS. CDDs were mainly involved in elements belonging to the protein metabolism and the TCA cycle. Protein-protein interaction analysis indicated that the interacting proteins in the major cluster were primarily involved in TCA cycle and protein metabolism. In the simple phenylpropanoids biosynthetic pathway of SFS, both phospho-2-dehydro-3-deoxyheptonate aldolase (PDA) and glutamate/aspartate-prephenate aminotransferase (AAT) were decreased at the protein level, but increased at the gene level. A confirmatory experiment indicated that protein ubiquitination and succinylation were more prominent during the early floral developmental stages, in correlation with simple phenylpropanoids accumulation. Taken together, those data indicates that phenylpropanoids metabolism and floral development are putatively regulated through the ubiquitination and succinylation modifications of PDA, AAT, and TCA cycle proteins in L. japonica.