Protein profiling of the potato petiole under short day and long day photoperiods

In potato (Solanum tuberosum), a signal is delivered from the leaf to underground organs to activate tuber formation. Short-day (SD) conditions induce tuberization and long-day (LD) inhibits the process. Recent studies have implicated a mobile RNA, StBEL5, as a potential signal in this process. The petiole constitutes an important vascular channel for the transport of light-mediated signals originating from the leaf blade and is also the transcriptional source of StBEL5 RNA. Hence, identifying the proteins in the petiole and their differential expression under SD and LD photoperiods will be helpful in further understanding the downstream signaling process. Thus, we have undertaken a proteomic analysis of proteins isolated from potato petioles (PP) grown under LD and SD photoperiod conditions using 2-dimensional gel electrophoresis (2-DE) followed by mass spectrometry based identification of proteins (a total of 125 proteins were identified from 185 spots). Sixty-seven differentially expressed proteins were identified in response to SD or LD photoperiods and an additional 43 putative phosphoproteins were identified through affinity enrichment. Numerous poly(U)-binding proteins which contain RNA recognition motifs have also been isolated and identified. This is the first comprehensive proteomics study that examines and catalogs proteins present in the potato petiole.