ZmARF16 Involved In Seminal Root Formation In Maize

As an important crop in the world,Maize（Zea mays L.）is widely distributed in the United States,China and other countries.However,maize needs more water and is sensitive to water stress.Overall,drought is the main factor limiting maize yield.As a direct source of soil water,the root system of maize plays an important role in its growth and drought resistance.Maize,as a typical whisker root plant,consists of a complex root system composed of many types of roots.seminal roots play an important role in the early development of maize,and the development of seminal roots is positively correlated with the yield of maize in the later stage.As an important hormone regulating plant growth and development,auxin is closely related to the development of maize seminal roots.As an most widely studied transcription factor in auxin signaling pathway,ZmARFs（Auxin response factors）play a very important role in root development.However,in maize,except ZmARF25 and ZmARF34,which has been proved to be involved in the regulation of seminal root development,the roles of other ARFs in seminal root development have not been studied.In this study,zmarfl 6 Uniform Mu of maize was obtained and its phenotype of root development was analyzed in detail.It was found that zmarfl6 had a phenotype of less seminal root number,shorter seminal root length and delayed germination.The root structure analysis of the mutant showed that the development of seminal root primordium was impaired in the zmarfl6,which resulted in fewer seminal roots in the later stage.The interaction between ZmARF16 and IAA8/12/21/25/28 was confimed by yeast two-hybrid and BIFC.The protoplast transient transformation experiment proved that ZmARF16 acts as a transcriptional activator to promote the expression of downstream genes.Through the analysis of transcriptome profiling of zmarfl 6,a list of genes in the Auxin signaly pathway showed difference in abundance we found that LBD38 was down-regulated in zmarf16 compared with W22.The results of qRT-PCR showed that the expression of LBD38 was significantly decreased in zmarf16.Auxin treatment of W22 induced the expression of LBD38,but not in zmarf16,This suggests that the expression of LBD38 induced by auxin depends on the ZmARF16 transcription factor.The cis-element analysis of the promoter region of LBD38 revealed that there were seven AuxREs（Auxin response elements）in the promoter region of 2Kb upstream of LBD38 ORF.Further yeast single hybridization and protoplast transient transformation experiments confirmed that ZmARF16 could directly binding to the promoter of LBD38 and promote its expression.In conclusion,our study shows that ZmARF16,as a transcriptional activator in the Auxin signal pathway,can interact with IAA8/12/21/25/28,etc.,and bind with the promoter region of LBD38 to promote its expression and regulate the development of seminal roots.