HOS15 encodes a WD40 protein. (A) Structure of HOS15 gene and its gene product. Positions are relative to the translation start site. The hos15 mutation is also indicated. The HOS15 protein contains two conserved domains: LisH (for Lissencephaly type-1-like homology motif, located between amino acids 5–37) and WD40 (the eight WD40-repeats are located as follow: 254–293, 309–352, 354–393, 396–434, 437–476, 479–527, 530–569, and 572–610). (B) Luminescence image of cold-treated (0°C for 24 h) hos15, WT, a representative line of hos15 transformed with an empty vector pCAMBIA1200 [hos15 (vector)], and a representative homozygous line of hos15 transformed with WT HOS15 gene (hos15 + HOS15). (C) Freezing tolerance of the plants shown in B at −5°C for 4 h. The plants were cold-acclimated (4°C for 7 d) before stress treatment. Photographs were taken 8 d after the treatment. (D) Comparison of HOS15 (accession no. AAL15328) with transducin-beta-like 1 (TBL1) proteins from human [TBL1a (O60907) and TBL1b (NP_078941.2)]. (E) HOS15 is slightly induced by stress treatments. Control, room temperature; cold, 0°C for 24 h; ABA, 100 μM ABA for 3 h; NaCl, 300 mM NaCl for 4 h.