Deactivation Of Endogenous GA Leads To A Semi-dwalf Maize

During the Green Revolution in the 1960 s,breeding dwarf cultivars turned out to be a landmark,leading to a significant increase in the production of wheat and rice globally.The most direct and effective strategy to cultivate dwarf crops is to reduce the level of endogenous gibberellins(GAs).GA 2-oxidases is a group of 2-oxoglutarate-dependent dioxygenases that catalyze the deactivation of bioactive GAs.GA2 ox can catalyze the bioactive GAs formation of inactive GAs through beta hydroxylation,thus maintain the balance of gibberellins in plants.Previous studies have successfully reduced the plant height and increased the yield of of genetically modified(GM)rice by accelerating the transformation of bioactive GAs to inactive GA.In addition,there is evidence indicated that GA plays a key role in plant response to drought stress.Previous studies have confirmed that under drought stress,the content of bioactive GAs was decreased significantly.Overexpression of GA2 ox family members can improve plant drought resistance,but the molecular mechanism is still unclear.In this study,the At GA2ox1 gene from Arabidopsis thaliana was cloned and overexpressed in maize.The effects of overexpression of At GA2ox1 on the growth and development and drought resistance of GM maize were studied by physiological,biochemical,and transcriptional methods.The feasibility of improving maize traits by inactivation of GA was analyzed.The main findings are as follows:1.The At GA2ox1 gene of Arabidopsis thaliana was cloned,and overexpression in maize which reduced the endogenous GA1 content of GM maize,and a semidwarf GM maize was obtained.2.Overexpression of At GA2ox1 gene changed the cell morphology of GM maize stem.The cells in the stem of GM maize became smaller,the density per unit area increased,and the vascular bundle cells were significantly deformed obviously.3.Overexpression of At GA2ox1 gene increased the chlorophyll content of GM maize by up to 2-fold and the root/shoot ratio by up to 1.8-fold compared with WT plant.4.Transcriptome analyses indicate that the expression patterns of 3 024 gene were changed in GM maize.Overexpression of At GA2ox1 altered the metabolic pathway of endogenous GA in GM maize,and enriches DEGs related to plant stress resistance and a variety of transcriptional factors,which may affect the growth and development of GM maize and the ability of drought resistance.5.Overexpression of At GA2ox1 gene improves the drought resistance of GM maize.Combined with physiological and biochemical experiment and transcriptome analysis,it was found that the drought resistance of GM maize was mainly improved by enhancing the osmotic stress resistance and reactive oxygen species scavenging ability.6.Based on two seasons of field trials,the GM maize exhibited a higher harvest index(increase by 9%-17%)and grain yield(increase by 10%-14%)to the control.