A b s t r a c t The wheat gene Rht (Reduced height) which predeterminated the success of «Green revolution» and has been employed in creation of plant varieties with reduced stem elongation and resistant to stem lodging, encodes a protein containing highly conserved DELLA domain (J. Peng et al., 1999). Many other high-yield dwarf varieties also possess mutations in the genes coding DELLA proteins. Since the mutations did not affect viability and reproducibility of the plants the usage of the

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... ations for advanced plant breeding might be very promising (M. Ueguchi-Tanaka et al., 2007). Along with dwarfism, some mutations in the genes can lead to an opposite phenotype: to tall plants with spindly stems, the so called slender forms. What phenotype (dwarf or slender plant) would be developed depends on functionality of a protein region affected by the mutation. The paper considers in depth structure, posttranslational modifications, cellular localization and functions of DELLA proteins. The proteins being participants of complex protein-protein interactions play a role of repressors in gibberellin (GA) signal transduction. In the absence/or small concentration of GA DELLA proteins interact with specific transcriptional factor (TF) targets blocking their DNA binding activity and as a result restrain plant growth. In the presence of GA stem elongation is activated because this hormone promotes destabilization of DELLA proteins, releasing TF from their repression. Thus, restrained growth of the rht mutant as well as other naturally occurring dwarf plants is associated with accumulation of DELLA proteins in a result of their high stability. In turn, enhanced stability of the proteins can be caused by mutations in functionally important domains of either DELLA proteins or other players of GA signaling such as receptor GID1 and F-box proteins (GID2 in rice; SLY1 in Arabidopsis) of E3 ubiqutin protein ligase. They all participate in complex proteinprotein interaction which is necessary for DELLA protein degradation via 26S-proteasome pathway (B.C. Willige et al., 2007; K. Hirano et al., 2010). The paper reviews a role of different functional motifs of DELLA protein in transduction of GA signal: DELLA, TVHYNP, polySTV on N-terminal part of a molecule and С-terminal GRAS-domain, containing the motifs LR, VHIID, PFYRE and SAW. DELLAproteins possess no DNA-binding site. Most probably their repressive function is associated with GRASdomain via protein-protein interaction of LR region with target TFs (R. Zentella et al., 2007; K. Hirano et al., 2010). The polySTV domain plays a regulator role. Post-transcriptional modifications in the region are potentially able to change partners in protein-protein interaction and/or cellular localization of the DELLA proteins (M. Ueguchi-Tanaka et al., 2005; K. Hirano et al., 2010). A function of DELLA protein as an integrator of hormone signal ways and external factors is also discussed. In the context the DELLA proteins are considered as «correctors» of plant growth reaction depending on growth conditions (X.-H. Gao et al., 2011). Thus, the activity of DELLA proteins might underlie the plant phenotypic flexibility and promotes restrained plant growth under unfavorable environmental conditions. Most dwarf plants possess mutations in DELLA proteins which repress gibberellic signal. These mutations, not affecting plant viability and reproducibility, are helpful in crop breeding [1]. The "Green revolution" which ensured an