AUTHOR=Guo Siyi , Dai Shaojun , Singh Prashant K. , Wang Hongyan , Wang Yanan , Tan Jeanie L. H. , Wee Wanyi , Ito Toshiro 

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

JOURNAL=Frontiers in Plant Science

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2018.00555

DOI=10.3389/fpls.2018.00555

ISSN=1664-462X

ABSTRACT=<p>In spite of short-day (SD) nature, rice (<italic>Oryza sativa</italic>) shares a conserved photoperiodic network for flowering control with long-day plants like <italic>Arabidopsis thaliana.</italic> 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 <italic>Ubiquitin</italic> promoter to produce the overexpressing lines <italic>OsNTL5∆C, OsNTL5</italic>∆C-<italic>SRDX</italic>, and <italic>OsNTL5∆C-VP</italic>, respectively in rice. The <italic>OsNTL5</italic>∆<italic>C-VP</italic> line showed an early-flowering phenotype. In contrast to this, the plants with <italic>OsNTL5</italic>∆C and <italic>OsNTL5</italic>∆C-<italic>SRDX</italic> 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 <italic>Early Heading Date 1</italic> (<italic>Ehd1</italic>), <italic>Heading Date 3a</italic> (<italic>Hd3a</italic>), and <italic>Rice Flowering Locus T1</italic> (<italic>RFT1</italic>) was significantly changed in the overexpression lines of <italic>OsNTL5</italic>∆<italic>C-VP, OsNTL5</italic>∆<italic>C</italic>, and <italic>OsNTL5</italic>∆<italic>C-SRDX</italic> as analyzed by Quantitative Real-time PCR. ChIP-qPCR and rice protoplasts assays indicate that OsNTL5 directly binds to the promoter of <italic>Ehd1</italic> and negatively regulates the expression of <italic>Ehd1</italic>, which shows antagonistic photoperiodic expression patterns of <italic>OsNTL5</italic> 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 <italic>Ehd1</italic>.</p>