ROLE OF NF-Y TRANSCRIPTION FACTORS IN ARABIDOPSIS EMBRYO DEVELOPMENT

Nuclear factor Y (NF-Y) is a trimeric transcription factor composed of three distinct subunits called NF-YA, NF-YB and NF-YC. In Arabidopsis thaliana, NF-Y subunits are known to play roles in many processes, such as embryogenesis, drought resistance, ABA signaling, flowering time, primary root elongation, Endoplasmic Reticulum (ER) stress response and blue light responses. Here, we report that the closely related NF-YA3 and NF-YA8 play an important role in Arabidopsis embryogenesis. Detailed GUS and in situ analyses showed that NF-YA3 and NF-YA8 are expressed in vegetative and reproductive tissues with the highest expression being during embryo development from the globular to the torpedo embryo stage. Plants from the nf-ya3 and nf-ya8 single mutants do not display any obvious phenotypic alteration, whereas nf-ya3 nf-ya8 double mutants are embryo lethal. Morphological analyses showed that the nf-ya3 nf-ya8 embryos are arrested at the globular stage and that both proembryo and suspensor are characterized by a disordered cell cluster with an irregular shape, suggesting defects in the determination of the apical-basal embryo axis. The suppression of both NF-YA3 and NF-YA8 gene expression by RNAi experiments resulted in defective embryos that phenocopied the nf-ya3 nf-ya8 double mutants, whereas complementation experiments partially rescued the globular-arrested nf-ya3 nf-ya8 embryos, confirming that NF-YA3 and NF-YA8 are required in early embryogenesis. Finally, the lack of GFP expression of the auxin responsive DR5rev::GFP marker line in double mutant embryos suggested that mutations in both NF-YA3 and NF-YA8 affect auxin transport in early developing embryos. Our findings indicate that NF-YA3 and NF-YA8 are functionally redundant regulators of the globular-heart transition that marks the acquisition of axiality during embryo development in Arabidopsis thaliana.