Functional Analysis of Duplicated NF-YB Genes in Photoperiod-Dependent Flowering
Carpenter, Emily Mills
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The heterotrimeric transcription factor NUCLEAR FACTOR Y (NF-Y) regulates photoperiod-dependent flowering and is composed of NF-YA, NF-YB, and NF-YC subunits. In higher plants, such as Arabidopsis thaliana, whole genome duplication (WGD) leads to an evolutionary expansion of NF-Y subunits. NF-YB and NF-YC proteins have a highly conserved histone-like fold domain (HFD) and flanking variable amino (N) and carboxy (C) terminals. NF-YB proteins have known roles in the control of floral induction, with the nf-yb2 nf-yb3 mutant displaying a late-flowering phenotype. To better understand their ability to regulate photoperiod-dependent flowering from a structure/function perspective, 10 NF-YB HFD were overexpressed in nf-yb2 nf-yb3. The HFD alone could rescue the late-flowering phenotype of nf-yb2 nf-yb3, except NF-YB4. While full-length NF-YB1 cannot rescue late flowering, while Full-length NF-YB2 rescues the nf-yb2 nf-yb3 phenotype, similar to wild-type. Chimeric experiments between NF-YB1 and NF-YB2 show that NF-YB2 N and C termini decrease the success of NF-YB1 HFD to rescue nf-yb2 nf-yb3. Meaning the N and C termini have evolved to modulate the functionality of the NF-YB HFD, and cannot enhance NF-YB1 HFD ability to promote flowering. My structure and function analysis of the NF-YB family displays a unique case of subfunctionalization called Escape from Adaptive Conflict (EAC), the ability of a duplicated gene to obtain a novel function while still maintaining its ancestral role. The ancestral role is designated in the HFD where most of the action for floral initiation resides, however, the variable N and C termini can only modulate the primary functionality of their native NF-YB HFD.
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