A novel protein fromBrassica napushas a putative KID domain and responds to low temperature

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Abstract
To identify factors that interact with histone deacetylase (HDAC) in Brassica napus, a yeast two‐hybrid library was screened using the Arabidopsis HDA19 as bait. A novel protein, bnKCP1, containing a putative kinase‐inducible domain (KID) was found to interact with HDA19. Southern blot analysis indicated that the bnKCP1 gene belongs to a small gene family of at least three members. Northern blot analysis showed bnKCP1 to be strongly expressed in stems, flowers, roots, and immature siliques, but not in leaf blades of seedlings. The accumulation of bnKCP1 transcript in the leaf blades was induced significantly within 4 h of exposure of B. napus seedlings to cold stress, whereas treatment of leaf blades with inomycin, an ionophore of Ca2+, caused a rapid (30 min) but transient induction of bnKCP1 expression. In contrast to that observed in leaf blades, expression of bnKCP1 in the stems was repressed upon cold treatment. In vitro and in vivo protein‐binding assays showed that bnKCP1 interacts with HDA19 via the KID domain, and that S188 is critical for bnKCP1–HDA19 interaction. BnKCP1 also exerted modest transactivation of the lacZ reporter gene in yeast through its N‐terminal region. These assays suggest that bnKCP1 may function as a transcription factor, which regulates gene expression through interaction with HDA19.