## 6 ARF Is Involved in Regulating Stress Response  
Abiotic stresses are the adverse effects of abiotic factors on plants, such as drought, flooding, salinity, mineral deficiencies, and excessively high or low ambient temperatures. Abiotic stresses affect plants in a variety of ways and can affect plant viability and development, which may result in changes in plant growth and crop yield, as well as disturbance of physiological processes such as photosynthetic rates or mineral uptake rates. Throughout their long evolutionary history, plants are constantly improving their ability to combat the adverse factors in the environment. The effects of stresses on plants, especially the negative ones, have indirectly affected human access to food and safety of life, and thus the study of various stresses in plants is also a hotspot.  
Numerous studies have shown that auxin response factor ARF plays an important regulatory role in abiotic stress responses in a variety of plants. In Arabidopsis, AtARF7 and AtARF19, members of 23 AtARFs, were suggested to be involved in the regulation of membrane lipid remodeling under phosphorus starvation stress, enhancing the low phosphorus adaptation in Arabidopsis [51]. SIARF4 is involved in the regulation of the response of tomato to salt and osmotic stress by decreasing stomatal conductance as well as increasing relative water content and abscisic acid content of leaves, and thus that tomato exhibits a higher tolerance to salt and osmotic stress [52]. Some other members of SIARF1, SIARF4, SIARF6A, SIARF7A, SIARF8A, SIARF9A, SIARF18, and SIARF19, can respond to abiotic stresses at the transcriptional level [53]. Rice is an important food crop worldwide, and OsARFs play a crucial role in the response of rice to abiotic stress. Both OsARF11 and OsARF15 exhibited unique expression patterns under salt stress, indicating that their involvement in rice response to salt stress [54]. [PERSON] et al. [55] concluded that most OsARF genes were inhibited by both cold and heat stress, with OsARF4/14/18/19 induced by cold stress and OsARF11/13/16 induced by heat stress. Nine ARFs genes were found to be involved in the response to drought stress, namely, OsARF2/4/10/14/16/18/19/22/23 [53]. In other plants, [PERSON] et al. [56] reported that NtARF6 and NtARF8 mediate plant growth and response to phosphorus starvation stress by regulating reactive oxygen species (ROS) steady-state and phosphorus uptake in tobacco. In Ipomoea batatas, IbARF5 is regulating salt tolerance and drought tolerance in plants [57].  
Biotic stresses are imposed by other organisms, such as pests, diseases, and weeds. Compared to the involvement of ARF in plant abiotic stress responses, less research has been conducted on the role of ARF in biotic stress responses. In studies of plant responses to biotic stress, it is relevant to report that in tomato biotic stress the _SIARF3_ gene's expression level is upregulated [33]. In rice, OsARF17 may be involved in plant defense responses to different types of arboviruses [11]. In fact, the effects of biotic stress are more serious, often resulting in crop yield, loss of fruit nutritional value, and even harm to human health. Therefore, study of ARF's participation in plant biotic stress response will be a valuable research direction in the future, potentially providing us with new solutions to practical production problems.