Functional Analysis Of A Calcium Sensor-Interacting Protein Kinase In Rice

Rice is one of the most important food crops for the entire world population. However, its growth and yield is greatly restricted under some field conditions due to the sensitivity to various stresses. Among them, salinity is a major factor at coastal areas and in irrigated farmlands. Salt stress is known to trigger a rapid and transient increase of free calcium concentration in plant cells. Following this Ca2+influx, signals are likely to be mediated by combinations of protein phosphorylation/dephosphorylation cascades. Protein kinases are key elements involved in signal transduction and play an essential role in salt tolerance in plants. In Arabidopsis, AtCIPK24/SOS2, the calcium sensor AtCBL4/SOS3 interacted protein kinase, was established for the first time on a calcium-dependent signaling chain in plant salt-stress signaling. Therefore, to identify more protein kinases on plant calcium-dependent in salt response will supply a promising approach to engineer increased salt-resistance. The main results are summarized as follows:1. An unknown gene was isolated from a rice seedling cDNA libaray. Amino acid alignment showed its high homology to CIPK protein kinase family from rice and Arabidopsis. We thought that this gene should be classified as rice CIPK family and renamed it as OsCIPK31. Over expression and RNA interference techniques have been widely used to identify specific gene function. Here, OsCIPK31 over-expression and RNAi transgenic plant lines were sucessfully constructed to further study its function.2. Transgenic plants overexpressing OsCIPK31 exhibited an increased sensitivity to salt stress during both seed germination and seedling growth. By contrast, transgenic lines underexpressing OsCIPK31 were significantly more tolerant to NaCl stress than the wild type. In response to salt stress, the OsCIPK31 under-expression rice accumulated more proline and presented higher K+/Na+ratio in shoots. Furthermore, several genes with functions in osmotic adjustment and ion homeostasis were identified to be differentially expressed in the transgenic plants. Together, the OsCIPK31 gene functioned as a negative regulator of salt stress tolerance in rice.3. To explore the interaction of OsCIPK31 with calcium sensor OsCBLs, a yeast two hybrid system was successfully performed between full length or C-terminal length of OsCIPK31 and OsCBL1-7. The results presented that C-terminal length of OsCIPK31 can interact with OsCBL3/6/7 in vivo, and indicated that OsCIPK31 may be involved in calcium-dependent salt response through the interaction of certein OsCBL.4. Another part of this work was about rice embryogenesis. In order to study the molecular mechnism of rice embryogenesis, we selected eight candidate genes with spectific expression during embryogenesis of rice. Over-expression transgenic plant lines were sucessfully constructed to further study their function. It remained to carry out subsequent experiments.