Zhang et al. discover how a tetratricopeptide repeat protein promotes heading by facilitating florigen transport in rice
Background: Hd3a and RFT1 are mobile flowering signals that promote the floral transition in rice and were proposed to function as florigens that play major roles under short-day conditions (SDs) and long-day conditions (LDs), respectively. Hd3a and RFT1 are synthesized in leaves and transported to the shoot apex to trigger the transition to flowering. OsFTIP1 (FT-INTERACTING PROTEIN1) is the only protein reported to mediate RFT1 transport in rice under LDs. Hd3a plays major roles in promoting flowering under SDs.
Question: How is Hd3a transported from leaves to the shoot apex in SDs? What is the function of tetratricopeptide repeat (TPR)-containing proteins in regulating heading date in rice?
Findings: We found that OsFTIP9 specifically regulates rice heading date under SDs by facilitating the transport of Hd3a from companion cells to sieve elements. Furthermore, we show that OsTPR075 interacts with both OsFTIP9 and OsFTIP1, which strengthens their respective interactions with Hd3a and RFT1. This in turn affects Hd3a and RFT1 trafficking to the shoot apical meristem, thus regulating heading date under SDs and LDs, respectively.
Next steps: Given that OsFTIPs and OsTPRs are important for the functions of protein transport complexes, we are interested in identifying additional interactors of these proteins and the crystal structures of OsFTIPs and OsTPRs. Moreover, it would be worth exploring the potential relevance of the FTIP-TPR interaction for members of the FTIP and TPR families involved in regulating flowering time in other plants.
Liang Zhang, Fan Zhang, Xuan Zhou, Toon Xuan Poh, Lijun Xie, Jun Shen, Lijia Yang, Shiyong Song, Hao Yu, and Ying Chen (2022). The tetratricopeptide repeat protein OsTPR075 promotes heading by regulating florigen transport in rice. https://doi.org/10.1093/plcell/koac190