Molecular basis of the dwarfism character in cultivated plants. I. Growth distortions due to mutations of gibberellin metabolism and signaling

Development of dwarf cereal varieties with improved mechanical stability of stems preventing their lodging led to significantly increased crop productivity in the 1960-1970s. The creation of novel high-yielding cultivars was one of the main purposes of the «Green revolution» aimed at the reorganization of agriculture in developing countries (G.S. Khush, 2001). At the current time the dwarfism character is of widely use in plant breeding. The dwarf varieties are not only resistant to lodging but also have higher nutrients-absorbing potential and often are more tolerant to diseases than traditional cultivars (K.U. Kurkiev et al., 2006). In connection with that the factors that predetermine plant growth have become of increasing scientific interest over recent years. Numerous dwarf cultivars produced during the «Green revolution» possessed mutant genes responsible for metabolism and transmission of gibberellic (GA) signal (M. Ueguchi-Tanaka et al., 2001; T. Sakamoto et al., 2004). GAs are involved in control of many stages of plant development, including seed germination, stem and root elongation (E. Tanimoto, 2012; P. Hedden, V. Sponsel, 2015). However, alternations at different steps of the GA-dependent processes might lead to different results: to plants with reduced height as well as to tall slender plants. Clear understanding the interaction of genetic and molecular mechanisms will facilitate the revealing of key molecular targets the changes in which would result in production of the desired dwarf varieties. The paper considers the ways of gibberellins biosynthesis, deactivation and how pool of active GAs is maintained. Among numerous known GAs, produced by plants, only GA1, GA3, GA4, GA5 and GA7 are physiologically active. GA20-oxidases and C3,β-oxidases (or C3,β-hydroxylases) involved in production of the active gibberellins catalyze final reactions of gibberellin biosynthesis. C2,β-oxidases are main enzymes that can quickly inactivate active GAs by adding a hydroxyl group (-OH) to a GA molecule. Modern concept about GA-signaling is reviewed according to the following established steps: GA receptor GID1; DELLA-proteins as the negative regulators in GA signaling; SCF E3-ubiqutin protein ligase and 26S proteasome; transcriptional factors with DNA-binding site; GA-regulated genes. Accumulated up-to-date data consider that in transmission of gibberellic signal a GA molecule initiates DELLA-protein degradation via interaction of GID1-DELLA complex with E3 SCFSLY1/GID2 (T.-P. Sun, 2011). Thus, reduced growth in dwarf cultivars can be associated with defects in biosynthesis of the active GAs or with accumulation of repressors of GA signaling, the DELLA-proteins, while GA-constitutive growth in tall slender forms might be caused by disturbance in work of GA-deactivation system or lack of the DELLA repressive function (H. Claeys et al., 2014). The paper also considers ways of participation of gibberellin in the complex hormone regulation of plant growth which occurs often via control over the repressive function of DELLA-proteins (P. Achard et al., 2003). A special attention is paid to characteristics of the genes that lead to altering plant growth, the dwarfism or gigantism.