Functional Analysis of a Conifer Protein that Interacts with the Global Transcriptional Regulator, Abscisic Acid Insensitive 3

ABI3 (Abscisic acid Insensitive 3) is an evolutionarily highly conserved transcription factor that is involved in seed development, stress signaling, and the induction and maintenance of seed dormancy. In previous work, the yellow-cedar (Callitropsis nootkatensis) ABI3 ortholog (CnABI3) was isolated and yeast two-hybrid approaches revealed CnAIP1 as a yellow-cedar protein that physically interacts with CnABI3. The CnAIP1 protein bears a high degree of similarity to eukaryotic heat shock protein associated factors, particularly those found in Arabidopsis (HIP1 and HIP2). CnAIP1::GUS reporter constructs expressed in Arabidopsis showed that the gene was temporally regulated during seed development, and its expression was enhanced in stressed seedlings. Seeds of CnAIP1-overexpressing Arabidopsis lines exhibited hypersensitivity to ABA and glucose as far as the inhibition of their germination was concerned, and their dormancy was enhanced. My results suggest that CnAIP1 is a positive regulator of seed development processes and works synergistically with CnABI3 to regulate dormancy.