Molecular Mechanism Of Transcription Factor OsARF7 Involved In The Root Development Dominated By Auxin In Rice

Roots are important organs for plant anchorage,water and nutrient absorption,and perceiving of soil environmental factors.The strong and well-developed roots of rice,characterized by its extensive distribution,vigorous activity,and delayed senescence,are essential for nutrient uptake,organ formation,organic allocation,and population structure optimization,which are important guarantees for high yield during the period of reproductive growth.OsARF7,a crucial transcription factor in the auxin signaling pathway,plays an important regulatory role in plant growth and development.Our previous studies have shown that OsARF7 mutation obviously affects the phenotype of roots in rice,however,the molecular regulatory mechanism of OsARF7 in root development is still unclear.In this study,osarf7 mutants and OsARF7-OE rice were employed to systematically investigate the effects of transcription factor OsARF7 on rice root development and to explore the molecular mechanism of OsARF7 involement in auxin signaling and its regulation of root development.The main results obtained are as follows:1.The number of adventitious roots of osarf7 mutant seedlings is significantly lower than that in the wild type ZH11 and OsARF7-OE plants,and the root length is also significantly shorter than that in the wild type ZH11 and OsARF7-OE plants.The number of adventitious root primordia formed at the stem base of the osarf7 mutant is also lower than those in wild type and OsARF7-OE plant.The result of fluorescence quantitative PCR showed that OsARF7 mainly express in the leaves and roots of rice,and GUS activity dyeing shows that OsARF7 mainly expressed in the elongation zone of rice adventitious roots and seminal roots.These findings suggest that the transcription factor OsARF7 mainly participates in rice adventitious root formation and root elongation,and positively regulates rice root development.2.Under the exogenous NAA treatment,the growth of osarf7 mutant plants is significantly inhibited,and the root length,root dry weight,plant biomass is significantly lower than those of wild type ZH11 and OsARF7-OE plants.Exogenous NAA treatment increases OsARF7 expression and enhances the GUS activity in the roots and embryonic base of positive OsARF7-promoter::GUS transgenic plants,indicating that the transcription factor OsARF7 is involved in the regulation of auxin on rice root elongation and adventitious root formation.3.Amino acid sequence analysis of the transcription factor OsARF7 reveals that it contains the typical B3-type DNA binding domain,auxin response conserved domain,and AUX/IAA binding domain.Evolutionary tree analysis shows that OsARF7 is most closely related to OsARF9 in rice and At ARF1 in Arabidopsis thaliana.Transcription factor OsARF7 is mainly situated in the nucleus of cell and has the self-transcription activation function,and the transcription activation domain located at the C-terminus of the amino acid sequence.4.Yeast two hybrid(Y2H)and bimolecular fluorescence complementation(Bi FC)techniques reveal that the transcription factor OsARF7 interacts with Os IAA7 protein in the Aux/IAA family.The expression level of Os IAA7 in the osarf7 mutant is higher than that in the OsARF7-OE plants.Exogenous auxin inhibits the expression of Os IAA7.Those results suggest that the expression of the transcription factor OsARF7 is negatively influenced by Os IAA7 protein.5.Using yeast one hybrid(Y187),dual-luciferase reporter assay,and electrophoretic mobility shift assay(EMSA),two important target genes,Os CRL1,are identified to be dominated by transcription factor OsARF7.The expression levels of Os CRL1 in the osarf7 mutant are higher than those in the OsARF7-OE plants,indicating that transcription factor OsARF7 negatively regulates the expression of Os CRL1.In addition,it is also found that the expression of OsARF7 is regulated by an upstream transcription factor Os MADS25 through interaction.In summary,these results in this study suggest that transcription factor OsARF7 transduces the auxin signal by interacting with Os IAA7 protein,and dominates the expression of Os CRL1,and then participates in the regulation of adventitious root formation and root elongation of rice seedling.