Isolation And Physiological Functions Analysis Of Casein Kinase I In Rice

Casein kinases are critical in cell division and differentiation across species. A rice cDNA fragment encoding a putative casein kinase I (CKI) was identified via cDNA macroarray under brassinosteroid (BR) treatment, and a full-length 1939 bp cDNA, OsCKI1, was isolated and found to encode a putative 463-aa protein. RT-PCR and Northern blot analysis indicated that OsCKI1 was constitutively expressed in various rice tissues and up-regulated by treatments with BR and abscisic acid (ABA). Enzymatic assay of recombinant OsCKIl proteins expressed in E. coli showed that the protein was capable of phosphorylating the specific substrate of CKIs-casein. The physiological roles of OsCKI1were studied through antisense transgenic approaches, and homozygous transgenic plants showed abnormal root development, including fewer lateral and adventitious roots, and shortened primary roots due to reduced cell elongation. Treatment of wild type plants with CKI-7, a specific inhibitor of CKI, also confirmed these functions of OsCKIl. Interestingly, in transgenic and CKI-7-treated plants, exogenously supplied IAA could restore normal root development, and measurement of free IAA content in CKI-deficient primary and adventitious roots revealed altered auxin content, indicating that OsCKI1 is involved in auxin metabolism or may affect auxin levels. Transgenic plants were less sensitive than control plants to ABA or BR treatment during germination, suggesting that OsCKIl may be involved in various hormone signaling pathways. OsCKI1-GFP fusion studies revealed the localization of OsCKI1 to the nucleus, suggesting a possible involvement in regulation of gene expression. In OsCAI1-deficient plants, differential gene expression was investigated usingcDNA chip technology, and results indicated that genes related to signal transduction and hormone metabolism were indeed with altered expression.