Systemic signaling in relation to regulation of flowering time

Abstract

In Arabidopsis thaliana, phloem proteome study is gaining recognition. An optimised EDTA exudation technique from excised leaves was incorporated in this study to formulate a method of obtaining sufficient phloem exudate protein. Total phloem exudate protein and excised gel bands from 1D SDS-PAGE yielded 221 identified proteins via analysis by LC-MS/MS. The majority of the proteins identified have functions in metabolic processes, stress response and defense mechanism. These may have been induced by wounding nevertheless many of these proteins may have been present within the companion cell and sieve element. Similar findings were reported in earlier Arabidopsis and other plant phloem proteome studies. A comprehensive list of Arabidopsis phloem exudate protein from three studies is presented here. Although the florigen protein FT was not identified in the main study, a different approach using MRM proved the presence of FT in the phloem exudate of Arabidopsis. An attempt to quantify FT was performed using MRM to test out if varying level of FT protein in response to photoperiod is produced in accordance to its mRNA expression as previously reported. Level of FT protein detected showed a pattern of expression different from FT mRNA level of expression. In an effort to detect long-distance movement of FT protein, transgenic lines carrying FT fused to Dendra2 and mediated by SUC2 and GAS1 promoters were generated. In spite of evidence of transcription of transgene, this experiment was unsuccessful with only weak expression detected in a few lines. Further validation could not be made due to time constraint. In summary, the protein data obtained from this study and the comprehensive list of compiled proteins serve as the basis of an Arabidopsis phloem proteome, and showed that quantification of level of FT protein in response to photoperiod is possible.