Analysis of desiccation-induced candidate phosphoproteins from Craterostigma plantagineum isolated with a modified metal oxide affinity chromatography procedure.

Reversible protein phosphorylation/dephosphorylation is crucial for regulation of many cellular events, and increasing evidence indicates that this post-translational modification is also involved in the complex process of acquisition of desiccation tolerance. To analyze the phosphoproteome of the desiccation tolerant resurrection plant Craterostigma plantagineum, MOAC-enriched proteins from leaves at different stages of a de-/rehydration cycle were separated by 2-D PAGE and detected by phosphoprotein-specific staining. Using this strategy 20 putative phosphoproteins were identified by MALDI-TOF MS and MS/MS, which were not detected when total proteins were analyzed. The characterized desiccation-related phosphoproteins CDeT11-24 and CDeT6-19 were used as internal markers to validate the specificity of the analyses. For 16 of the identified proteins published evidence suggests that they are phosphoproteins. Comparative analysis of the 2-D gels showed that spot intensities of most identified putative phosphoproteins change during the de-/rehydration cycle. This suggests an involvement of these proteins in desiccation tolerance. Nearly all changes in the phosphoproteome of C. plantagineum, which are triggered by dehydration, are reversed within 4 days of rehydration, which is in agreement with physiological observations. Possible functions of selected proteins are discussed in the context of the de-/rehydration cycle.