A Membrane-Bound NAC-Like Transcription Factor OsNTL5 Represses the Flowering in Oryza sativa

In spite of short-day (SD) nature, rice ( ) shares a conserved photoperiodic network for flowering control with long-day plants like Flowering or heading is an important agronomic trait in rice. NAC transcription factors (TFs) are well-conserved and one of the largest families of plant TFs. However, their function in flowering or heading time is not well-known yet. A preferential expression of a membrane-bound NAC-like TF OsNTL5 in developing leaves and panicles of rice indicated to us its putative role in flowering. To examine its function, three independent constructs was generated, one with a deletion in the C terminus membrane-spanning domain (OsNTL5∆C), OsNTL5∆C fused with the SRDX transcriptional repressor motif and OsNTL5∆C used with the VP16 activation domain under the promoter to produce the overexpressing lines ∆C- , and , respectively in rice. The ∆ line showed an early-flowering phenotype. In contrast to this, the plants with ∆C and ∆C- showed a very strong late-flowering phenotype, suggesting that OsNTL5 suppresses flowering as a transcriptional repressor. The protein subcellular localization assay suggested that N-terminal part of the OsNTL5 is localized to the nucleus after the protein is cleaved from its membrane-spanning domain at the C-terminal end and functions as a TF. Expression of flowering genes responsible for day length signals such as ( ), ( ), and ( ) was significantly changed in the overexpression lines of ∆ ∆ , and ∆ as analyzed by Quantitative Real-time PCR. ChIP-qPCR and rice protoplasts assays indicate that OsNTL5 directly binds to the promoter of and negatively regulates the expression of , which shows antagonistic photoperiodic expression patterns of in a 24-h SD cycle. Hence in conclusion, the NAC-like TF OsNTL5 functions as a transcriptional repressor to suppress flowering in rice as an upstream factor of .