SEC13B Interacts with Suppressor of Frigida 4 to Repress Flowering.

SECRETORY13 (SEC13) is an essential member of the coat protein complex II (COPII), which was reported to mediate vesicular-specific transport from the endoplasmic reticulum (ER) to the Golgi apparatus and plays a crucial role in early secretory pathways. In , there are two homologous proteins of SEC13: SEC13A and SEC13B. () encodes a C2H2-type zinc finger protein that inhibits flowering by transcriptionally activating the () through the FRIGIDA (FRI) pathway in . However, it remains unclear whether SEC13 proteins are involved in flowering. In this study, we first identified that the mutant exhibited early flowering under both long-day and short-day conditions. Quantitative real-time PCR (qRT-PCR) analysis showed that both and were expressed in all the checked tissues, and transient expression assays indicated that SEC13A and SEC13B were localized not only in the ER but also in the nucleus. Then, we identified that SEC13A and SEC13B could interact with SUF4 in vitro and in vivo. Interestingly, both and single mutants flowered earlier than the wild type (Col-0), whereas the double mutant flowered even earlier than all the others. In addition, the expression of flowering inhibitor was down-regulated, and the expressions of flowering activator (, ( and ( were up-regulated in , and mutants, compared with Col-0. Taken together, our results indicated that SEC13B interacted with SUF4, and they may co-regulate the same genes in flowering-regulation pathways. These results also suggested that the COPII component could function in flowering in .