Phosphorylation of aldose-6-phosphate reductase from Prunus persica leaves.

Sugar-alcohols are major photosynthates in plants from the Rosaceae family. Expression of the gene encoding aldose-6-phosphate reductase (Ald6PRase), the critical enzyme for glucitol synthesis in rosaceous species, is regulated by physiological and environmental cues. Additionally, Ald6PRase is inhibited by small molecules (hexose-phosphates and inorganic orthophosphate) and oxidizing compounds. This work demonstrates that Ald6PRase from peach leaves is phosphorylated in planta at the N-terminus. We also show in vitro phosphorylation of recombinant Ald6PRase by a partially purified kinase extract from peach leaves containing Ca2+-dependent protein kinases (CDPKs). Moreover, phosphorylation of recombinant Ald6PRase was inhibited by hexose-phosphates, phosphoenolpyruvate and pyrophosphate. We further show that phosphorylation of recombinant Ald6PRase was maximal using recombinant CDPKs. Overall, our results suggest that phosphorylation could fine-tune the activity of Ald6PRase.

Ancient signal for nitrogen status sensing in the green lineage: Functional evidence of CDPK repertoire in Ostreococcus tauri.

Calcium-dependent protein kinases (CDPKs) regulate plant development and many stress signalling pathways through the complex cytosolic [Ca2+] signalling. The genome of Ostreococcus tauri (Ot), a model prasinophyte organism that is on the base of the green lineage, harbours three sequences homologous to those encoding plant CDPKs with the three characteristic conserved domains (protein kinase, autoregulatory/autoinhibitory, and regulatory domain). Phylogenetic and structural analyses revealed that putative OtCDPK proteins are closely related to CDPKs from other Chlorophytes. We functionally characterised the first marine picophytoeukaryote CDPK gene (OtCDPK1) and showed that the expression of the three OtCDPK genes is up-regulated by nitrogen depletion. We conclude that CDPK signalling pathway might have originated early in the green lineage and may play a key role in prasinophytes by sensing macronutrient changes in the marine environment.

Activation of a calcium-dependent protein kinase involved in the Azospirillum growth promotion in rice.

Rice seedlings (Oryza sativa) inoculated with the plant growth-promoting rhizobacteria Azospirillum brasilense FT326 showed an enhanced development of the root system 3 days after inoculation. Later on, a remarkable enlargement of shoots was also evident. An increase in the Ca2+-dependent histone kinase activity was also detected as a result of inoculation. The biochemical characterization and Western-blot analysis of the kinase strongly supports the hypothesis that it belongs to a member of the rice CDPK family. The fact that the amount of the protein did not change upon inoculation seems to indicate that a posttranslational activation is responsible for the change in the enzymatic activity. An in-gel kinase experiment identified a 46 kDa CDPK like protein kinase as a putative component of the signal transduction pathway triggered by Azospirillum inoculation. To our knowledge, this is the first report on the possible involvement of a Ca2+-dependent protein kinase in promotion of rice plants growth by A. brasilense.

The calcium-dependent protein kinase (CDPK) and CDPK-related kinase gene families in Hevea brasiliensis-comparison with five other plant species in structure, evolution, and expression.

Calcium-dependent protein kinases (CDPKs or CPKs) play important roles in various physiological processes of plants, including growth and development, stress responses and hormone signaling. Although the CDPK gene family has been characterized in several model plants, little is known about this gene family in Hevea brasiliensis (the Para rubber tree). Here, we characterize the entire H. brasiliensis CDPK and CDPK-related kinase (CRK) gene families comprising 30 CDPK genes (HbCPK1 to 30) and nine CRK genes (HbCRK1 to 9). Structure and phylogeny analyses of these CDPK and CRK genes demonstrate evolutionary conservation in these gene families across H. brasiliensis and other plant species. The expression of HbCPK and HbCRK genes was investigated via Solexa sequencing in a range of experimental conditions (different tissues, phases of leaf development, ethylene treatment, and various abiotic stresses). The results suggest that HbCPK and HbCRK genes are important components in growth, development, and stress responses of H. brasiliensis. Parallel studies on the CDPK and CRK gene families were also extended to five other plant species (Arabidopsis thaliana, Oryza sativa, Populus trichocarpa, Manihot esculenta, and Ricinus communis). The CDPK and CRK genes from different plant species that exhibit similar expression patterns tend to cluster together, suggesting a coevolution of gene structure and expression behavior in higher plants. The results serve as a foundation to further functional studies of these gene families in H. brasiliensis as well as in the whole plant kingdom.