Abstract: 【Objective】Nuclear transcription factor Y (NF-Y) belongs to a transcription factor gene family widely existing in eukaryotic. NF-Y-like transcription factors are involved in the process of gene expression regulation of plant growth and development and stress responses. So far, it is never been reported that NF-Y-like transcription factors are involved in plant resistance to low nitrogen stress. In this study, a NF-Y-like transcription factor gene SiNF-YA6 was isolated from millet, and its characteristics and biological function were identified.【Method】A NF-Y-like transcription factor gene SiNF-YA6 highly up-regulated by low nitrogen stress was selected from the results of transcriptome sequencing of millet treated by low nitrogen. DNAMAN and MEGA6.0 software were used to make the phylogenetic tree of NF-YA6. The Real-time PCR was used to analyze expression patterns of SiNF-YA6 under different treatments. SiNF-YA6 was transformed into Arabidopsis protoplast to observe its subcellular localization. SiNF-YA6 was overexpressed in Arabidopsis to identify gene function.【Result】SiNF-YA6 is 714 bp in length and encoding 237 amino acids. SiNF-YA6 contains a CBF conservative domain with 62 amino acids. Phylogenetic tree analysis showed that NF-YA was fell into 6 classes, and SiNF-YA6 belongs to the fifth class. SiNF-YA6 was the highest homology with a rice NF-YA protein (Os03g07880) (77.4%). Expression pattern analysis showed that NF-YA6 was induced by low nitrogen stress, and its expression reach peak after treatment for 5 d that raised about 5 times compared with the expression level at the beginning of treatment. While transcription of SiNF-YA6 under high salt, drought, ABA treatment also showed a trend of increasing. SiNF-YA6 under SA and GA treatments was no obvious different. Tissue specific expression analysis showed that SiNF-YA6 mainly expressed in millet roots. Subcellular localization indicated that SiNF-YA6 was mainly located on the plasmalemma and nucleus in plant cell. Results of low nitrogen stress resistance test showed that the main root length and root surface areaof SiNF-YA6 transgenic Arabidopsis were significantly higher than in wild type Arabidopsis, and the fresh weight of transgenic plants was also significantly greater than the wild type plants (P<0.01) under low nitrogen stress (total nitrogen content of 1 mmol·L^-1), and the growthof SiNF-YA6 transgenic Arabidopsis showed no obvious difference with wild-type Arabidopsis under SA and GA treatments. Those results indicated that overexpression of SiNF-YA6 gene significantly enhanced transgenic plants resistance to low nitrogen stress. The downstream genes, including some nitrogen transporter genes (NRT2.1 and NRT2.4), were up-regulated in SiNF-YA6 transgenic Arabidopsis. However, SiNF-YA6 transgenic Arabidopsis showed no obvious difference with wild-type Arabidopsis under high salt and drought stresses.【Conclusion】Overexpression of SiNF-YA6 enhanced transgenic plants tolerance to low nitrogen stress by up-regulated expression of several nitrogen transporter genes, which will give new candidate for improvement of the nitrogen use efficiency in crops.

Key words:  foxtail millet (Setaria italica), NF-YA transcription factor, function analysis, low nitrogen stress