Liu et al. elucidate the regulation of FT movement by a MCTP-SNARE complex.
Plant Cell https://doi.org/10.1105/tpc.18.00960
By Lu Liu and Hao Yu, Department of Biological Sciences and Temasek Life Sciences Laboratory, National University of Singapore, Singapore
Background: The transition to flowering is the most dramatic phase change in flowering plants, which is crucial for reproductive success. Plants respond to various environmental and developmental signals to determine when they should flower. In the model plant Arabidopsis thaliana, these flowering signals converge on the regulation of FLOWERING LOCUS T (FT), which encodes part of the mobile floral stimulus called florigen that moves from leaves to the shoot apex to trigger the formation of flowers. As an essential step in this trafficking process, FT protein is known to move from companion cells (specialized cells in the phloem of the plant vascular system where FT is originally expressed) to sieve elements (the conducting cells of the phloem) in leaves, through which FT travels to the shoot apex.
Question: Although our understanding of FT trafficking is progressing, the mechanisms underlying which FT protein transports from companion cells to sieve elements across the intercellular connections known as plasmodesmata (PDs) remain largely elusive.
Findings: We show that the plasma membrane-resident syntaxin-like Q-SNARE, SYNTAXIN OF PLANTS 121 (SYP121), interacts with QUIRKY (QKY), a member of the family of multiple C2 domain and transmembrane region proteins (MCTPs), to regulate FT movement to the plasma membranes of companion cells through membrane-bound compartments called endosomes. This mediates the export of FT from companion cells to sieve elements, thus affecting FT trafficking to the shoot apex and flowering time under long days.
Next steps: In our future studies, we will further identify regulators and the relevant mechanisms that affect FT transport from leaves to the shoot apex. We will also investigate how this trafficking process is influenced by various environmental conditions.
Lu Liu, Chunying Li, Zhi Wei Norman Teo, Bin Zhang, and Hao Yu. (2019). The MCTP-SNARE Complex Regulates Florigen Transport in Arabidopsis. Plant Cell; DOI: https://doi.org/10.1105/tpc.18.00960
Key words: flowering time, florigen, trafficking, MCTP, SNARE