The Study On Improving Rice Agronomic Traits By OsHOX7 Gene

Rice（Oryza sativa L.）is the main food crop,and the increase of rice yield is an urgent requirement to meet the future needs of mankind.Rice agronomic traits are important factors affecting rice yield,including plant height,tiller angle,tiller number and grain morphology.Plant height has a certain influence on the lodging resistance and yield of rice.Using gene to improve rice plant height and studying the molecular effects of rice dwarfing can provide theoretical guidance for using genetic engineering and other molecular breeding techniques to improve rice agronomic traits,which is of great significance for cultivating ideal rice with high yield,high resistance and high quality.The regulation of plant type is often the result of the interaction of a complex regulatory network of plant hormones and transcription factors.HD-Zip transcriptional factors are widely involved in plant cell differentiation,growth and development,and hormone response.At present,among the four subfamilies of HD-Zip,there are relatively few research reports on subfamily II,and the function of OsHOX7 gene of this subfamily in rice has not yet been reported.In this study,bioinformatics,expression pattern,subcellular localization and interaction protein analysis of OsHOX7 were carried out after cloning OsHOX7.By constructing OsHOX7 overexpression and interference vectors to transform rice,the transgenic OsHOX7 materials were subjected to phenotype identification,gibberellin（GA）metabolism and signal transduction-related gene transcription level analysis,and seeds quality evaluation to study the effect of this gene on rice agronomic traits.The main work is as follows:（1）Cloning,bioinformatics and expression pattern analysis of OsHOX7 geneThe OsHOX7 gene was cloned from rice Zhonghua 11（ZH11）.The gene is 1,050 bp in length.Its bioinformatics analysis shows that the protein encoded by OsHOX7 consists of 349 amino acids,and it is predicted that it may be located in the nucleus.The upstream promoter region of OsHOX7 was found to have elements CAT＿box related to meristem expression and RY-element involved in seed-specific regulation.CARE＿motif involved in GA response and cis-acting element TATC-box involved in GA response were also found.The phylogenetic tree shows that OsHOX7 is closely related to Ta HDZ3.Amino acid homology comparison results show that OsHOX7 has conserved HD and Zip domains.Analysis of temporal and spatial expression patterns showed that the OsHOX7gene expressed the highest level in the leaves at the filling stage and mature stage.（2）Subcellular localization and interaction protein analysis of OsHOX7The 35S::OsHOX7-GFP fusion expression vector was constructed and expressed in tobacco epidermal cells.The results showed that the protein encoded by OsHOX7 gene was localized in the nucleus.The results of yeast two-hybrid experiment showed that OsHOX7 was no autoactivation activity,and it interacted with rice DELLA protein SLR1.（3）Effects of overexpression OsHOX7 gene on rice plant height35S::OsHOX7 overexpression and OsHOX7-RNAi interference vectors were constructed to obtain OsHOX7 transgenic plants.Phenotype analysis of OsHOX7overexpression plants showed that the plant height was reduced,showing semi-dwarfing.At the mature stage,the internodes of OsHOX7 overexpression plants were significantly shortened,and the length and width of the second internode cells were significantly shortened,but the lignin and vascular bundle size did not change significantly.（4）OsHOX7 gene is involved in the regulation of GA pathwayUnder the induction of gibberellic acid（GA₃）,the transcription of OsHOX7 gene may be inhibited.After applying GA₃ to OsHOX7 overexpression seedlings,it was found that the elongation rate was increased compared with the wild type,and the plant height could be partially restored.In addition,in the up-regulated and down-regulated plants of OsHOX7 gene,the transcription level of GA metabolism and signal transduction related genes changed.In the OsHOX7 overexpressed plants,the transcription levels of the GA degrading enzyme genes Os GA2ox1,Os GA2ox3,Os GA2ox5 and the GA core suppressor SLR1 were significantly up-regulated,while the expression of these genes in the OsHOX7interference plants showed the opposite situation.（5）Quality assessment of OsHOX7 overexpression riceThe length and thickness of OsHOX7 overexpression rice grains were increased and decreased compared with wild-type grains,but there was no significant difference in1000-grain weight.Analyzing the starch of OsHOX7 overexpression and wild-type rice grains showed that the size,solubility,swelling degree and total content of starch in the OsHOX7 overexpression rice grains were not significantly different from those of the wild-type.The analysis of the protein composition of rice revealed that compared with the wild-type,there was no significant difference in the total protein,gluten,gliadin and albumin content of the OsHOX7 overexpression rice,but the globulin content increased.