Five NUCLEAR FACTOR-Y subunit B genes in rapeseed (Brassica napus) promote flowering and root elongation in Arabidopsis

Abstract

Heterologous expression of BnNF-YB2, BnNF-YB3, BnNF-YB4, BnNF-YB5, or BnNF-YB6 from rapeseed promotes the floral process and also affects root development in Arabidopsis. The transcriptional regulator NUCLEAR FACTOR-Y (NF-Y) is a heterotrimeric complex composed of NF-YA, NF-YB, and NF-YC proteins and is ubiquitous in yeast, animal, and plant systems. In this study, we found that five NF-YB proteins from rapeseed (Brassica napus), including BnNF-YB2, BnNF-YB3, BnNF-YB4, BnNF-YB5, and BnNF-YB6 (BnNF-YB2/3/4/5/6), all function in photoperiodic flowering and root elongation. Sequence alignment and phylogenetic analysis showed that BnNF-YB2/3 and BnNF-YB4/5/6 were clustered with Arabidopsis AtNF-YB2 and AtNF-YB3, respectively, implying that these NF-YBs are evolutionarily and functionally conserved. In support of this hypothesis, the heterologous expression of individual BnNF-YB2, 3, 4, 5, or 6 in Arabidopsis promoted early flowering under a long-day photoperiod. Further analysis suggested that BnNF-YB 2/3/4/5/6 elevated the expression of key downstream flowering time genes including CO, FT, LFY and SOC1. Promoter-GUS fusion analysis showed that the five BnNF-YBs were expressed in a variety of tissues at various developmental stages and GFP fusion analysis revealed that all BnNF-YBs were localized to the nucleus. In addition, we demonstrated that the heterologous expression of individual BnNF-YB2/3/4/5/6 in Arabidopsis promoted root elongation and increased the number of root tips formed under both normal and treatment with simulators of abiotic stress conditions.