AUTHOR=Lee Areum , Jung Haemyeong , Park Hyun Ji , Jo Seung Hee , Jung Min , Kim Youn-Sung , Cho Hye Sun 

TITLE=Their C-termini divide Brassica rapa FT-like proteins into FD-interacting and FD-independent proteins that have different effects on the floral transition

JOURNAL=Frontiers in Plant Science

VOLUME=13

YEAR=2023

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2022.1091563

DOI=10.3389/fpls.2022.1091563

ISSN=1664-462X

ABSTRACT=<p>Members of the FLOWERING LOCUS T (FT)-like clade of phosphatidylethanolamine-binding proteins (PEBPs) induce flowering by associating with the basic leucine zipper (bZIP) transcription factor FD and forming regulatory complexes in angiosperm species. However, the molecular mechanism of the FT–FD heterocomplex in Chinese cabbage (<italic>Brassica rapa</italic> ssp. <italic>pekinensis</italic>) is unknown. In this study, we identified 12 <italic>BrPEBP</italic> genes and focused our functional analysis on four <italic>BrFT-like</italic> genes by overexpressing them individually in an <italic>FT</italic> loss-of-function mutant in <italic>Arabidopsis thaliana</italic>. We determined that <italic>BrFT1</italic> and <italic>BrFT2</italic> promote flowering by upregulating the expression of floral meristem identity genes, whereas <italic>BrTSF</italic> and <italic>BrBFT</italic>, although close in sequence to their Arabidopsis counterparts, had no clear effect on flowering in either long- or short-day photoperiods. We also simultaneously genetically inactivated <italic>BrFT1</italic> and <italic>BrFT2</italic> in Chinese cabbage using CRISPR/Cas9-mediated genome editing, which revealed that <italic>BrFT1</italic> and <italic>BrFT2</italic> may play key roles in inflorescence organogenesis as well as in the transition to flowering. We show that BrFT-like proteins, except for BrTSF, are functionally divided into FD interactors and non-interactors based on the presence of three specific amino acids in their C termini, as evidenced by the observed interconversion when these amino acids are mutated. Overall, this study reveals that although <italic>BrFT-like</italic> homologs are conserved, they may have evolved to exert functionally diverse functions in flowering <italic>via</italic> their potential to be associated with FD or independently from FD in <italic>Brassica rapa</italic>.</p>