Proteomic analysis of the early development of the Phalaenopsis amabilis flower bud under low temperature induction

Phalaenopsis amabilis, one of the most important flowers in the current international flower market, is a plant that undergoes vernalization and requires low temperature treatment for flowering. There have been few reports on the proteomic analysis of the development of flower buds. In this study, by using isobaric tags for relative and absolute quantification (iTRAQ), 4096 differentially expressed proteins were identified in P. amabilis under low temperature treatment, of which 42 were associated with early floral induction, and 18 were verified by mass spectrometry multi-reaction monitoring (MRM). Among the proteins associated with the vernalization pathway, PEQU_11434 (glycine-rich RNA-binding protein GRP1A-like) and PEQU_11045 (UDP-N-acetylglucosamine diphosphorylase) were upregulated compared to their expression in control flower buds. It was therefore inferred that O-GlcNAc glycosylation was involved in the posttranscriptional modification of VRN1 (API homolog) and that the GRP2 protein (glycine-rich RNA-binding protein) was glycosylated to relieve binding to the VRN1 mRNA precursor to promote the expression of VRN1, which initiates floral development. Furthermore, phytochromes A (PEQU_13449, PEQU_35378), B (PEQU_09249) and C (PEQU_41401) were downregulated under low temperature treatment compared to their expression in control flower buds, suggesting that they could repress the expression of the VRN2 gene and thus release its repression of VRN3 to enable the high-level expression of FTPEQU_19304 (FT, VRN3 homolog), which promotes VRN1 expression and then stimulates flowering.