Exploration of specific properties and functions of specific members of the NF-Y family

In yeast and mammals, the transcription factor nuclear factor Y (NF-Y) is composed of the subunits A, B and C and binds to the CCAAT box cis-elements. While human and animals encode the three subunits of NF-Y each in single copy gene, Arabidopsis thaliana possesses 10, 13 and 13 genes encoding the NF-Y subunits A, B and C, respectively. A few individual plant NF-Y subunits have been described to be involved in a number of important biological processes. Based on previous expression profiles of all NF-Y genes in Arabidopsis thaliana during development and in response to stress conditions, some candidate genes for NF-Y subunits were selected for detailed analysis. Specific polyclonal antibodies raised against the selected NF-Y subunit confirmed the presence of the corresponding subunit in wild-type (WT) and overexpressor plants. The selected NF-Y genes were analyzed on their cell-specific expression pattern during plant development by using promoter: GUS fusion gene constructs in stable transformed Arabidopsis plants. Histochemical analysis revealed that the GUS expression was induced in NF-YB3: GUS plants responding to wounding. Quantitative RTPCR experiments suggested that NF-YB3 is involved in wounding stress responses. A reverse genetic approach was used to examine the functions of the NF-Y subunits under abiotic stress. The loss-of function nf-yb3 and nf-ya5 plants both exhibited delayed flowering under long-day (LD) conditions. This indicates that NF-YB3 and NF-YA5 are necessary for photoperiod-dependent flowering. Transcript analysis suggested that the expression of FLOWERING LOCUS T (FT) and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1) was reduced in absence of NF-YB3 or NF-YA5. These results underlined the existing model, in which a NF-Y complex interacts with CONSTANS (CO) to control flowering time through regulating the expression of FT in Arabidopsis. In addition to changes in flowering time, NF-YA5 plays a role in plant growth and development. A dwarf phenotype was observed in 35S: NF-YA5 plants. These morphological alterations of NF-YA5 overexpressor plants were not rescued by the application of exogenous gibberellins (GA). The anatomical analysis revealed that the leaf cell of 35S: NF-YA5 plants was smaller than WT. This suggested that NF-YA5 plays a role in leaf cell elongation.