Characterization of a pumpkin mRNA encoding a Cyclin-Dependent Protein Kinase (CDK) potentially involved in phloem development

The phloem is involved in the delivery of nutrients but also of long-range signals that regulate diverse processes. Several different RNAs have been found in the phloem translocation stream, which could have a role in signaling. In a previous work, we have found several RNAs in pumpkin phloem sap exudates in response to viral infection, among them a transcript encoding a potential cyclindependent protein kinase (CDK). In this study, we report the further characterization of the aforementioned CDK mRNA. The complete sequence of this mRNA, which we termed CmCDKP (for Cucurbita maxima CDK from Phloem), was obtained (GenBank no. AIQ82912.1). The phylogenetic analysis of the virtual translation of this sequence showed that CmCDKP is closely related to those involved in transcriptional regulation via RNA polymerase II CTD phosphorylation, or splicing control. The mRNA accumulated to highest levels in pollen tissue. Interestingly, the mRNA localized to the companion cell-sieve element complex in the phloem, developing phloem, and also in isolated cells in the shoot apical meristem, suggesting a role in early phloem development.