Actinidia DRM1 - An Intrinsically Disordered Protein Whose mRNA Expression Is Inversely Correlated with Spring Budbreak in Kiwifruit

Abstract

Intrinsically disordered proteins (IDPs) are a relatively recently defined class of proteins which, under native conditions, lack a unique tertiary structure whilst maintaining essential biological functions. Functional classification of IDPs have implicated such proteins as being involved in various physiological processes including transcription and translation regulation, signal transduction and protein modification. Actinidia DRM1 (Ade DORMANCY ASSOCIATED GENE 1), represents a robust dormancy marker whose mRNA transcript expression exhibits a strong inverse correlation with the onset of growth following periods of physiological dormancy. Bioinformatic analyses suggest that DRM1 is plant specific and highly conserved at both the nucleotide and protein levels. It is predicted to be an intrinsically disordered protein with two distinct highly conserved domains. Several Actinidia DRM1 homologues, which align into two distinct Actinidia-specific families, Type I and Type II, have been identified. No candidates for the Arabidopsis DRM1-Homologue (AtDRM2) an additional family member, has been identified in Actinidia.

The Dormancy MarkerDRM1/ARPAssociated with Dormancy but a Broader RoleIn Planta

“…Multiple protein sequence alignments show high conservation of the DRM1/ARP protein product, with two domains clearly identifiable at the aminoterminus and at the carboxy-terminus [7,25]. This high conservation across species, and indeed monocotyledons and Dicotyledons, suggests a potential importance of the action of this protein in the normal development and physiology of plants.…”

“…Dormancy release experiments performed with AdDRM1, the DRM1/ARP homologue in Actinidia deliciosa (kiwifruit), using hydrogen cyanamide (commercially available as HiCane) as a dormancy release agent show the same expression profiles [7]. Treatment with hydrogen cyanamide was used to release the apical buds from endodormancy (compared with decapitation initiating release of apical buds from paradormancy in pea and Arabidopsis).…”

“…Cyclin-dependent kinases (CDKs) are known to be involved in the reinitiation of cell cycle progression through the G 1 -S phase transition [8]. As AdDRM1 levels decrease, AdCDKB expression increases [7].…”

“…Recently evidence has emerged for DRM1/ARP family members as intrinsically disordered proteins (IDPs) [7]. IDPs, found in plants and animals, have a large proportion of their sequence yielding no fixed tertiary structure, yet still providing some biological function [29].…”

“…Data from kiwifruit have shown that sucrose levels accumulate in dormant buds over winter and reduce again prior to bud break in spring [63]. Indeed, application of hydrogen cyanamide is associated with a rapid decrease in both detectable sucrose levels [63] and DRM1/ARP transcript levels [7].…”