Functions Of Arabidopsis Casein Kinase1-Like2in Abscisic Acid Signal Transduction Pathways

Casein Kinase (CK) is a Ser/Thr protein kinase which is widespread ineukaryotic cells, the ATP and GTP is used as phosphate donor in this kind of enzyme.There are two main subcategories in CK family, CK1and CK2. Casein kinase ishighly conserved, mainly located in cytoplasm, nucleus, cell membrane andmitochondria, and involved in a variety of metabolic processes. CK1and CK2playimportant roles in many physiological progresses such as root development, planthormone signaling, macromolecular transport, circadian rhythms, cell cycle, DNAtranscription, RNA translation, protease degradation, nuclear transport, viralinvasion, light signal transduction, SA mediated signal transduction, stressresistance, and seed storage, etc.In this study we investigated possible functions of Casein Kinase1-Like2(CKL2) of Arabidopsis CK gene family members in abscisic acid signal transductionpathways. The RT-PCR results showed that CKL2was expressed in all tissuesespecially in leaf and leaf stalk. The expression level of CKL2gene in wild typeseedlings was extremely high when after2hours treatment with10μM ABA, andthen returned to normal at4hours post-treatment.A homozygous T-DNA insertion mutant line ckl2was identified using threeprimers PCR method. Through the experimental data of germination rate (underdifferent treatment of ABA, NaCl and Mannitol), root length, water loss rate,stomatal aperture and Pro-accumulation assay, we found that the mutant showedABA-hyposensitive phenotype in all the tests. There are obvious differences of theexpression level of ABA and abiotic stress responsive genes (ABF3, ABI3, ABI5,DREB1, KIN1, and SOS3) between ckl2and wild type. These results further provedthat CKL2gene could participate in the ABA signaling transduction pathways. Bycomparing the expression level of ABA-upregulated genes (RD29A, RD29B, RD22,RAB18) in ckl2and wild type after treated with10μM ABA, we found that theexpressions of all these genes were consistently less in ckl2compared with wild type.The above results indicated that CKL2gene might act as a key component thatpositively mediated ABA signalling in Arabidopsis. This study provides animportant reference to investigate the physiological functions of the other membersof the CK gene family.