## 3 ARF Is Involved in Regulating Root Development  
Roots are the nutritional organs of plants, usually located below the ground surface, and are responsible for absorbing water and dissolving inorganic salts from the soil, as well as supporting, reproducing, and storing and synthesizing organic matter. [PERSON] et al. [16] reported that microRNA160-targeted AtARF10/AtARF16 plays a crucial role in root cap formation. In rice, OsARF1 is also able to regulate crown roots [17]. Another ARF of rice species is OsARF12, which plays an active role in promoting root elongation [18].  
The formation of lateral roots plays a key role in plant development, as well as the ability of plants to obtain nutrients depends on the degree of root branching. Numerous studies have suggested that auxin is a common signal for the formation of lateral roots. In Arabidopsis, AtARF5 is essential for lateral root formation [19]. In the root tissue of seedlings, AtARF7 and AtARF19 are transcriptional activators of early auxin response genes and control the expression of most plant auxin response genes. They regulate lateral root formation through direct activation of LBD/ASLs, as well as AtARF7 and AtARF19 double mutations caused impaired hypocotyl and root development [20]. In tomato, SlARF2  
Figure 2: A model of ARFs involved in leaf development and senescence in _Arabidopsis thaliana_. ARF2/3/4/5 regulates leaf flattening by targeting the promoters of WUSCHEL-RELATED HOME-OBOX1 (WOX1) and PRESSED FLOWER (PRS). ARF3/5/7 synergistically regulate the leaf formation process. ARF 7 and 19 affect leaf expansion. ARF1 and 2 promote leaf senescence.  
regulates the formation of lateral roots, and high expression of SIARF2 promotes lateral root growth [14].  
In addition to lateral roots, ARF genes also play an important role in adventitious root development. _AtARF6_ and _AtARF8_ genes regulate adventitious root formation with the involvement of micro160 and micro167, and AtARF6 has been shown to positively control the development of adventitious roots. It has also been shown that AtARF17 is involved in this process and negatively regulates adventitious roots in Arabidopsis [21]. In rice, crown rootless1 (_OsCRL1_) encodes a plant-specific protein, and OsARF1 binds directly to AuxRE in the OsCRL1 promoter, which plays an important role in adventitious root initiation [22]. In addition, [PERSON] et al. [23] reported PeARFs may play diverse regulatory roles in adventitious root development of Populus.  
The functions of auxin in primary root formation have also been studied for a long time in the field of developmental biology. In Arabidopsis thaliana, primary root formation in early embryogenesis of is initiated with the specification of a single cell called hypopphysis. This initial step requires the auxin-dependent release of the transcription factor MONOPTEROS (MP)/ARF5 from its inhibition by the Aux/IAA protein BODEN-LOS (BDL)/ IAA12 [24]. In addition, [PERSON] et al. [25] found that MP may play a role by directly regulating the expression of miR390 in Arabidopsis thaliana primary root meristem. [PERSON] et al. [26] showed that MP controls embryonic root initiation by regulating a mobile transcription factor.