Expression analysis of sugarcane shaggy-like kinase (SuSK) gene identified through cDNA subtractive hybridization in sugarcane (Saccharum officinarum L.).

Identification of genes whose expression enables plants to adapt to any kind of stresses is integral to developing stress tolerance in crop plants. In this study, PCR-based cDNA suppression subtractive hybridization technique was used to construct sugarcane salt (NaCl) stress specific forward and reverse subtracted cDNA library. For this, mRNAs were pooled from the shoot and root tissues stressed with NaCl (200 mM) for various time intervals (0.5 to 18 h). Sequencing the clones from the forward subtracted cDNA library, we identified shaggy-like protein kinase (hereafter referred as sugarcane shaggy-like protein kinase, SuSK; NCBI GenBank EST database Acc: FG804674). The sequence analysis of the SuSK revealed homology to Arabidopsis thaliana shaggy-related protein kinase delta (E value, 1e(-108)), dzeta and iota. Alignment of the catalytic domain sequence of GSK-3/shaggy-like kinase with partial sequence of SuSK performed using ClustalW tool indicated kinase active-site signature sequence. Spatial and temporal transcript expression profiling of the SuSK gene based on Real-Time PCR revealed significant induction of transcript expression in response to short-term salt (NaCl 200 mM) or polyethylene glycol-8,000 (PEG; 20% w/v) induced osmotic stress in leaves and shoots of sugarcane plants. The transcript expression increased progressively under salt stress and reached to 1.5-fold of the control up to 8 h treatment. In response to PEG stress, the transcript expression increased by 1.5-fold over the control in 2-h treatment in leaf, whereas in shoots, the expression remained unchanged in response to the various treatments. Differences in growth parameters, relative water content, and membrane damage rate were statistically insignificant in the short-term salt or PEG-stressed plants as compared to the control, non-stressed plants. Expression analysis revealed the differential and temporal regulation of this gene under salt and PEG stress and that its early induction may indicate involvement in stress signaling.