Analysis Of Tillering Characteristics,Carbon-Nitrogen Metabolism And The-Related Gene Expression In Rice Tiller Suppression Mutants Ts1 And Ts2

Rice tillering,one of the most important agronomic traits that may influence panicle numbers and further affect grain yield,is controlled by multiple factors such as endogenous physiology and biochemistry,hormones,genes and exogenous environmental factors.Studying the genetic variation of tiller number,further excavating the genetic factor that affect rice tillers,and revealing its underlying molecular mechanism,and then molecularly modifying the tillering and earing of rice will be an important direction for rice ideal plant breeding.The subjects of this study are two rice tiller suppression mutants ts1 and ts2,which were induced by EMS.We observed their tillering characteristics under field conditions,and analyzed the key enzyme activities of carbon and nitrogen metabolism in rice and tillering-related genes expression.The main result are represented as below1.Both of rice tiller suppression mutants ts1 and ts2 exhibited tiller suppression phenotype,but there is something different.Mutant ts1 showed tiller suppression phenotype and its growth has been retardation through the whole growth period,while the ability to tillering of mutant ts2 was only inhibited in early vegetative growth and released in later growth period.2.The histological observation of the axillary buds in mutant tsl and mutant ts1 revealed that the axillary buds of the mutant ts1 and mutant ts2 have normal tissue structures at each leaf position and they both have bud primordia and young leaves,which indicates that the axillary buds in the mutants tsl and ts1 had potential to differentiate into normal tiller and the tiller suppression phenotypes of the mutants tsl and ts2 were not caused by abnormal formation of tiller buds.3.The contents of soluble sugar,soluble protein,free amino acid,and the activities of glutamine synthase(GS),glutamate synthase(GOGAT),glutamate dehydrogenase(GDH)in the mutant tsl were significantly lower than those in the wild type LY95,thus indicating that the carbon and nitrogen metabolic intensity in the mutant tsl is significantly weaker than the wild type,which caused the growth of the mutant tsl is retarded and the supply of nutrition in axillary bud was not sufficient,then resulting in the tiller suppression phenotype.4.The nitrogen assimilation efficiency of mutant ts2 was significantly lower than the wild type in the early vegetative stage,and excess nitrogen was accumulated then triggered nitrogen stress.In response to nitrogen stress,the content of free amino acid in the mutant ts2 increased.Meanwhile,the carbon metabolism and related enzyme activity of mutant ts2 were significantly lower than the wild type,which indicating that the decrease of carbon and nitrogen metabolism is an important reason for the inhibition of tiller in the early stage of vegetative growth.In the later stages of vegetative growth,The nitrogen metabolism ability of the mutant ts2 recovered,the plants were no longer under nitrogen stress,the content of free amino acid returned to normal,and nitrogen assimilation products accumulated rapidly;at the same time,the carbon metabolites and related enzyme activities in the mutant ts2 also returned to the same level as the wild type.The tillering ability of the mutant ts2 was released in the late stage of vegetative growth.5.In the early stage of vegetative growth of the mutant tsl,the phenotypes of tiller suppression were exhibited under the action of multiple pathways such as auxin,strigolactone,and tillering pathways,but these multiple pathways were greatly weakened in the later period of vegetative growth.However,the growth status of the mutant tsl was continuously suppressed during the growth period,and the nutrient supply to the axillary buds could not fully meet their growth needs,thus resulting in a lower potency of the mutant tsl than that of the wild type,which means the mutant tsl still showing a phenotype of tillering inhibition.6.The accumulation of the cytokinin receptor gene Cgal was induced by excess accumulation of nitrogen and cytokinin synthesis genes in the mutant ts1 during the early vegetative growth period,and up-regulation of Cgal gene expression resulted in the appearance of dark green leaves,suppression of tillering,and semi-dwarf phenotype.The gene expression in the strigolactone pathway in the mutant ts2 was also significantly up-regulated,and these factors together caused the phenotype of tillering inhibition in the mutant ts2 in the early stage of vegetative growth.In the late period of vegetative growth,the nitrogen level in the mutant ts2 returned to normal,and the expression of cytokinin synthesis gene and Cgal gene was no longer induced.And multiple pathways including auxin pathway,strigolactone pathway,and tiller pathway worked together to induce the tillering in mutant ts2 in the late vegetative growth stage.