Homologous NF-YC2 Subunit from Arabidopsis and Tobacco Is Activated by Photooxidative Stress and Induces Flowering

The transcription factor NF-Y consists of the three subunits A, B and C, which are encoded in Arabidopsis in large gene families. The multiplicity of the genes implies that NF-Y may act in diverse combinations of each subunit for the transcriptional control. We aimed to assign a function in stress response and plant development to NF-YC subunits by analyzing the expression of NF-Y genes and exploitation of nf-y mutants. Among the subunit family, NF-YC2 showed the strongest inducibility towards oxidative stress, e. g. photodynamic, light, oxidative, heat and drought stress. A tobacco NF-YC homologous gene was found to be inducible by photooxidative stress generated by an accumulation of the tetrapyrrole metabolite, coproporphyrin. Despite the stress induction, an Arabidopsis nf-yc2 mutant and NF-YC2 overexpressors did not show phenotypical differences compared to wild-type seedlings in response to photooxidative stress. This can be explained by the compensatory potential of other members of the NF-YC family. However, NF-YC2 overexpression leads to an early flowering phenotype that is correlated with increased FLOWERING LOCUS T-transcript levels. It is proposed that NF-YC2 functions in floral induction and is a candidate gene among the NF-Y family for the transcriptional activation upon oxidative stress.