Abstract: SnRK2 ( sucrose non-fermenting 1-related protein kinases 2 ) represents a unique family of protein kinase in regulating signaling transduction in plants .
Although the regulatory mechanisms of SnRK2 have been well demonstrated in Arabidopsis thaliana , their functions in maize are still unknown .
In our study , we cloned an SnRK2 gene from maize , ZmSAPK8 , which encoded a putative homolog of the rice SAPK8 protein .
ZmSAPK8 had two copies in the maize genome and harbored eight introns in its coding region .
We demonstrated that ZmSAPK8 expressed differentially in various organs of maize plants and was up-regulated by high-salinity and drought treatment .
A green fluorescent protein ( GFP ) -tagged ZmSAPK8 showed subcellular localization in the cell membrane , cytoplasm and nucleus .
In vitro kinase assays indicated that ZmSAPK8 preferred Mn ( 2+ ) to Mg ( 2+ ) as cofactor for phosphorylation , and Ser-182 and Thr-183 in activation loop was important for its activity .
Heterologous overexpression of ZmSAPK8 in Arabidopsis could significantly strengthen tolerance to salt stress .
Under salt treatment , ZmSAPK8-overexpressed transgenic plants exhibited higher germination rate and proline content , low electrolyte leakage and higher survival rate than wild type .
Further analysis indicated that transgenic plants showed increased transcription of the stress-related genes , RD29A , RD29B , RAB18 , ABI1 , DREB2A and P5CS1 , under high-salinity conditions .
The results demonstrated that ZmSAPK8 was involved in diverse stress signal transduction .
Moreover , no obvious adverse effects on growth and development in the ZmSAPK8-overexpressed transgenic plants implied that ZmSAPK8 was potentially useful in transgenic breeding to improve salt tolerance in crops .
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