| AtCREl has been known to be a cytokinin receptor in Arabidopsis. The CRE1 protein contains CHASE domain at the N-terminal part, followed by a transmitter (histidine kinase) domain and two receiver domains. The N-terminal CHASE domain of CRE1 is the putative recognition sites for cytokinin. It has been proposed that cytokinins detected by a two-component system. Two-component systems use a histidine kinase as an environmental sensor and rely on a phosphorelay for signal transduction that are common in microorganisms. In rice, less is known about cytokinin signaling and the CHASE domain containing proteins. Blast search in NCBI database, five CHASE domain containing proteins were found in rice genomic sequences. OsCRLla, OsCRLlb, OsCRL2, OsCRL3, and OsCRL4. OsCRLla, OsCRLlb, OsCRL2 and OsCRLS contain the four domains existing in CRE1, whereas OsCRL4 only contains the CHASE domain and a putative Ser/Thr protein kinase domain. The expression and functional of OsCRL4 were investigated. The results were summarized as follows:1. The CHASE domain family of rice containing five genes, named as OsCRLla, OsCRLlb, OsCRL2, OsCRLB, and OsCRL4 based on the homology with histidine kinase of Zea mays. Phylogenetic alignment analysis indicates that OsCRLla and OsCRLlb have the lowest relationship with AtCREl and OsCRL4 has the lower homology with AtCREl.2. The results of RT-PCR analysis showed that OsCRL4 was mainly expressed in root and developed spikelets. A detailed examination was performed with transgenic plants with OsCRL4:: & -glucuronidase -(GUS) gene, GUS staining was observed in lateral roots and the tip of developed spikelets. Transverse and longitudinal sections of lateral root of the transgenic plants showed that OsCRL4 expressed in phloem and peridermof the lateral roots.3. 35S::OsCRL4 was construction and used for AtCREl mutation transformation. The results showed that OsCRL4 can complement the phonetype of Atcrel-lmuta.tion.
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