Research On The Dynamics Of Phytohormones Regulation Of Root Growth In Arabidopsis Thaliana

Root is an important organ of plants.The formation and growth of roots are not only determined by their own genes,but also influenced by environmental conditions.The former is embodied by the expression of genes,while the latter is realized by signal transduction mechanism.A variety of regulatory relationships in the root system form a complex biological network,in which phytohormones play a crucial role.Therefore,although experimental studies provide increasingly rich details,a comprehensive understanding of life activities requires grasp the overall behavior of complex biological networks rather than piecing details together.The characteristics of complex biological networks determine that most of the regulatory actions are nonlinear,and there are often crosstalks between different pathways,and noises may have a significant impact on the system behavior.Consequently,in order to understand the intrinsic mechanism of plant root growth and development regulation,it is significant to study the crosstalks between regulatory pathways and the effect of noises on the overall behavior of the system in the process of nonlinear regulation.In this paper,chemical reaction kinetics,nonlinear stochastic theory and numerical simulation method are used to study the stress response mechanism based on abscisic acid and the mechanism of lateral root formation based on auxin in Arabidopsis thaliana root.The nonlinear dynamics and the effect of noises were deeply analyzed.The following results were obtained:(1)Through the analysis of the mechanism of growth inhibition and stress response of Arabidopsis thaliana root cells,the dynamics of the crosstalk between the two major signaling pathways and its significance to the survival of plants were revealed.There are crosstalks between the two major regulatory pathways(abscisic acid pathway and RALF-FER pathway)in the system.The experimental results show that although both of them play the role of growth inhibition individually,the total effect is not simply superimposed,but the inhibition of growth is reduced under certain conditions.A simplified network model and the corresponding chemical reaction kinetic equations are established to dissect this nontrivial regulation behavior.The steady-state solution of the simplest model equation is analyzed by an analytic parameter-free approach based on the derivation chain rule.It is found that:(i)The non-linear regulatory exponents were introduced to describe the two regulatory actions of which the mechanism is not yet clear,our analysis reveals a simple constraint on them.(ii)Under above constraint,the non-monotonic regulatory behavior of RALF on growth inhibition arises when the level of abscisic acid above a critical threshold decided by RALF concentration,which moderates the hypersensitivity of abscisic acid pathway under stress conditions.Our results point out that besides the role of normal growth inhibitor,RALF also plays a moderator of abscisic acid responses under stresses to protect plants from damage caused by hypersensitive reactions by ABA-RALF crosstalks.In addition,the constraint relationship between the two non-linear regulatory exponents is instructive for the further study of the corresponding regulatory actions.The analytic parameter-free approach based on topological structure used in this study could be useful for the study of reaction networks with only topological structure in the absence of data.(2)The dynamics of feedback and feedforward motifs in the lateral root formation mechanism of Arabidopsis thaliana(Arabidopsis thaliana)and the effects of noise on the system behavior were studied.The occurrence of lateral root primordium in the main root depends on the spatial distribution of auxin,and its formation depends on the polar transport of auxin,in which PIN3 transporter is very important.A simplified network model composed of coherent feedforward and negative feedback for PIN3 regulation is established based on biological phenomena.The dynamics and intrinsic noise properties as well as the effects of feedforward and feedback are studied.The numerical algorithm of multiplicative noise is used to analyze the influence of external noise on the behavior of the system in original model.The results show that the simplified model exhibits continuous oscillation and damping oscillation with the change of dynamic structure.The effects of feedforward and feedback on dynamics and intrinsic noise also depend on the dynamic structure of the system.The coherent feedforward with "or" gate form results in the response delay of the system to external auxin stimuli,can also be seen as a memory effect,which has a significant buffering and smoothing effect on the fluctuation of PIN3 response induced by auxin disturbance,thus enhancing the stability of PIN3 expression.Based on the defined quantitative index of memory effect,it is found that the increase of noise intensity in negative feedback plays an opposite role in two aspects of memory effect,while the increase in noise intensity in feedforward parameter has little effect on the two aspects of memory effect.It is shown that the coherent feed-forward motif can reduce the influence of noise.