Triticeae Genomics and Genetics, 2025, Vol.16, No.4, 175-183 http://cropscipublisher.com/index.php/tgg 176 taproot, also called the seed root, which grows directly from the seed and is the basis of the entire root system. The number, length and growth angle of the seed roots vary greatly among different barley varieties (Robinson et al., 2016). The taproot will grow lateral roots outward, which allow the root system to explore a larger area of soil so that the plant can absorb more water and nutrients (Wang et al., 2021). In addition, there is a kind of root called adventitious root, which grows from the stem node. They mainly help plants to fix in the soil and absorb resources, especially when the plants grow larger and approach maturity, these roots are particularly important (Oyiga et al., 2019). 2.2 Root system response under different soil and nutrient conditions The barley root system is particularly sensitive to soil and environmental changes. For example, in drought, the root growth of most varieties will slow down. However, some varieties can keep their roots longer or change their angles to go deeper into the soil to find water. Some root traits related to drought are controlled by specific genes, including some transcription factors and signal genes for responding to stress (Siddiqui et al., 2024). If the soil is acidic, it will also affect the root structure. Different varieties perform very differently in this environment. Some varieties have longer roots and more biomass, which shows that varieties that adapt to acidic soils can be cultivated (Abebe et al., 2024). In addition, traits such as root thickness, length and total root weight are affected by the amount of nutrients. Some studies have found some QTLs that can help plants adapt to low-fertilizer soils (Farooqi et al., 2023). 2.3 Influence on water absorption and crop productivity How well the root system grows directly affects the ability of barley to absorb water and nutrients, which will be reflected in the yield. If the roots grow deep and at a steeper angle, they can usually draw water from deeper soil layers, which is particularly advantageous in drought conditions and leads to higher yields (Figure 1) (Jia et al., 2019). Longer roots and greater biomass are usually associated with better plant growth, more grains, and larger grains, all of which indicate that strong roots are important for yield (Manju et al., 2019). Of course, the relationship between roots and yield may vary in different environments, but in general, the number and angle of roots are more closely related to yield (Robinson et al., 2018). Optimizing root structure through breeding and genetic improvement is a promising direction. Doing so can make barley more adaptable to different environments and help increase yields (Wang, 2024). 3 Regulatory Role of Transcription Factors in Root Development 3.1 Overview of transcription factors in plant root systems Transcription factors (TFs) are proteins that can bind to DNA. They can control the "on" or "off" of specific genes, and play a major role in root growth, cell differentiation, and plant response to various stresses (such as drought or pests and diseases) (Chen et al., 2022). Transcription factors recognize specific fragments on DNA and pull other proteins to work together, thereby affecting the structure, absorption capacity and environmental adaptability of roots (Strader et al., 2021). 3.2 Major TF families involved in barley root regulation: ARF, NAC, MYB, WRKY In barley root development, some transcription factor families are particularly critical. For example, MYB is the largest one. It regulates the differentiation and cell cycle of root cells, and can also help plants cope with drought, salinity and nutrient deficiency. MYB also affects the signaling of plant hormones and is expressed in many root tissues. It is one of the core players in root gene regulation (Chen et al., 2022; Liu et al., 2023; Zhang et al., 2025). Transcription factors such as WRKY are also important, especially when plants are exposed to stress (such as lack of fertilizer), they can regulate the development of roots. These factors work together with other transcription factors to form a complex regulatory network to control root growth and adaptability (Bakshi and Oelmüller, 2014; Wani et al., 2021). There are also transcription factors such as ARF (auxin response factor) and NAC, which play a major role in the regulation of plant auxin and also play a key role in root development and stress response, and may have similar functions in barley. 3.3 Interaction with plant hormone signaling Transcription factors often work together with hormone signaling pathways in plants to regulate root structure.
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