The Role Of Microfilament Binding Protein VLN1 In Regulating Root Hair Growth In Arabidopsis

The formation of root hair increases the surface area of the roots and accelerates the absorption of water and nutrients from the external environment.The growth and development of root hair have a great influence on the growth of plants.At the same time,root hair as a single cell also provides a model system for the study of plant cell differentiation and elongation.The termination of root hair growth can accurately control the length of the root hair and the maturity time.However,at present,there are few studies on the molecular mechanism of root hair growth termination.Based on the important function of thick actin bundles in the apex and subapex in the termination of root hair growth,we revealed the role of VLN1 in terminating root hair cell elongation by bundling actin filaments.(1)GUS and GFP signal analysis showed that VLN1 was highly expressed in both long and short root hair cells,including the apical and sub-apical regions.It also indicated that VLN1 could specifically act on the microfilament skeleton of root hair.(2)Through genetic analysis,further studies showed that the loss of VLN1 function delayed the growth of root hairs,which resulted in the longer root hairs.On the contrary,overexpression of VLN1 resulted in the shorter root hairs and the growth stopping time was nearly 3 hours earlier than that of wild type.While the root hairs length and growth process of restored mutant plants were similar to that of wild type plants.(3)The loss of VLN1 function led to a significant decrease in the bundle frequency of actin filaments in the apex and subapex regions of root hairs,a significant decrease in thick actin bundles,a significant increase in the frequency of microfilament cutting and depolymerization,and a significant decrease in the maximum filament length and longevity in the apex and subapex regions of root hair.(4)GL2 is an important transcription factor.Genetics analysis showed that the root hair of Gl2 mutant was longer than that of wild type,the growth stopping time was delayed by nearly 2 hours,and its overexpression showed completely opposite results.(5)Ch IP results showed that GL2 could directly recognize VLN1.(6)RT-q PCR and GUS staining analysis showed that the expression of VLN1 in gl2 mutant refractory plants was significantly lower than that in wild type plants,while the expression of VLN1 in over-expressed materials was significantly higher,which demonstrated that GL2 positively regulated the transcriptional expression level of VLN1 gene.(7)The loss of GL2 function led to the termination of root hair growth in Arabidopsis thaliana.The microfilament morphology similar to that of the vln1 mutant was found in the apical and subapical regions,in other words,the lack of thick actin filament bundles.On this basis,the overexpression of VLN1 could compensate for this defect,and the corresponding microfilament bundle formation rate increased significantly.In conclusion,this study demonstrates that VLN1 plays an important role in the process of root hair growth by bundling the subapical and apical microfilaments of root hair cells,and the regulation of root hair growth by VLN1 is regulated by transcription factor GL2,which provides a new evidence for the regulation mechanism of root hair growth and the function of VLN1 in vivo.