The Functional Identification And Mechanism Analysis Of Lateral Root Inducing Compound LRI1

Plant roots can effectively absorb water and nutrients which was strongly dependent on root architecture.For taproot plants,the branching and expansion of the root system was achieved through the development of lateral root,which was largely controlled by the plant hormone auxin.But the multiple effects of auxin and auxin analogues on roots complicated the study of lateral root development.But the application of small molecule compounds could have unexpected effects.Compared with traditional genetic methods,the application of small molecule compounds had obvious advantages in the analysis of plant biology.For example,the technology is simple,the start-up cost is low,and the problems of lethality and functional redundancy can be effectively avoided.Small molecules had made major breakthroughs in revealing plant hormone signal pathways,signal cascades,signal transduction and plant defense mechanisms.In this paper,we successfully identified a small molecule compound named compound of lateral root inducer1(LRI1).Its structure is different from known auxin and its analogues,but it can effectively promote lateral root formation.In this experiment,we took LRI1 as a chemical tool and took the representative dicot plant Arabidopsis thaliana to conduct a preliminary study on its root architecture.It was found that the primary root(PR)became shorter and the lateral root(LR)was enhanced under LRI1 treatment.Then,under the treatment of LRI1,the viability of Arabidopsis root tip meristem,cell cycle activity,auxin accumulation,root clock frequency,number of lateral root prebranch sites,morphology and number of lateral root primordia were detected to explore the regulation of LRI1 on Arabidopsis lateral root development.Meanwhile the screening and identification of mutants were also performed.The main research results are as follows:1.Combined with chemical genetic screening and structural analysis,a compound significantly increased the number and density of lateral root was successfully identified.The molecular structure is different from known auxins and their analogs.This compound was named Compound of lateral root inducer1(LRI1)for research.2.LRI1 can significantly promote the number of lateral root in Arabidopsis thaliana,increase lateral root density,suppress the elongation of the primary root and present a concentration gradient effect,but it has no obvious effect on the monocot model rice.3.LRI1 can induce the auxin signal in the root system,increase the accumulation of auxin,speed up the frequency of the oscillation signal in the root tip oscillation zone,and increase the number of prebranch sites.Meanwhile,the number of lateral root primordia at each stage increased significantly,but the shape didn’t change.Eventually LRI1 promoted the occurrence of lateral roots in Arabidopsis.At the same time,LRI1 can delay the root cell cycle,bring out the cell division activity of the root tip meristem to decrease,reduce the number of root tip meristem cells,suppress the primary root elongation.4.Using forward genetics,we successfully screened mutants that are hypersensitive to LRI1: LRI1 hypersensitive1(lri1s1)and LRI1 hypersensitive2(lri1s2)and mutants that are not sensitive to LRI1:LRI1 resistant1(lri1r1),LRI1 resistant2(lri1r2)and LRI1 resistant3(lri1r3).5.The study of lri1r2 mutants found that lri1r2 alleles showed complete insensitivity to the lateral root induction effect of LRI1.Hybridization of lri1r2 with wild-type Col-0 showed that the phenotype of lri1r2 was caused by a pair of alleles.Sex gene control;hybridize lri1r2 with wild-type Ler,and perform preliminary gene mapping of F2 population,and found that lri1r2 alleles may be located between the two genetic markers T20P8 and T16B24 on chromosome 2.The full text showed that LRI1 induced auxin signal,increased auxin accumulation,speeded up the frequency of the root clock,increased the number of prebranch sites,and promoted the number of lateral roots in Arabidopsis.It can attenuate the expression of the root tip cell cycle,reduce the cell viability of the root tip meristem,and suppress the elongation of the primary root.LRI1 regulated the expression of downstream target genes with affecting a certain part of the auxin signaling pathway,and ultimately regulated the development of Arabidopsis lateral root.The results of this experiment laid a foundation for the subsequent search and identification of key pathways and related genes regulating lateral root development.