Maize Genomics and Genetics 2025, Vol.16, No.4, 219-228 http://cropscipublisher.com/index.php/mgg 220 Therefore, this study intends to use overexpression materials to focus on verifying the functions of several key phosphate transporters and see exactly how they affect the absorption and internal distribution of phosphorus in corn. During the research process, molecular analysis, physiological data and phenotypic observations will be combined to identify those "star transporters" that may have the potential to improve phosphorus utilization efficiency. The ultimate goal is to provide ideas for future breeding and reducing reliance on chemical fertilizers, and to promote the greener and more efficient development of corn production. 2 Phosphate Transporter Families in Maize: Classification, Genomics, and Expression 2.1 Classification and diversity of phosphate transporter gene families When it comes to phosphate transporters in corn, the PHT1 family is almost the most thoroughly studied. In B73 corn, researchers identified 13 PHT1 genes (from ZmPHT1;1 to ZmPHT1;13), they are mainly responsible for absorbing phosphorus from the soil into plants (Liu et al., 2016). However, it is not only PHT1 that exists in corn; PHT2 and PHT3 also occupy positions in the system - PHT2 is more commonly found in plastids, while PHT3 is related to mitochondria. This indicates that these proteins each have their own functions. For instance, the SPX family, although not the main force in translucency, also plays its own role in phosphorus signaling and homeostasis. Studies have identified as many as 33 SPX genes (Xiao et al., 2021), which is actually not a small number. 2.2 Genomic organization and evolutionary relationships From the perspective of chromosome distribution, the PHT1 gene is not concentrated together. In corn, these 13 genes are distributed on chromosomes 1, 2, 5, 7, 8 and 10. They are not randomly present - many of them can be traced back to gene replication that occurred at different times. Some replication events occurred in modern times, such as ZmPHT1; 1 and ZmPHT1; 9; And ZmPHT1; 1 and ZmPHT1; The relationship between 13 might be even earlier. These replication activities illustrate the process of genome expansion. Phylogenetic studies have found that these genes of corn are closely related to the corresponding genes of rice, sorghum and short-stemmed grass, indicating that their functions are likely conserved in the Poaceae family (Su et al., 2013). However, one point cannot be ignored: whether monocotyledonous or dicotyledonous, many plants have undergone polygenic replication of the transporter family, which is obviously a trace left by earlier evolutionary events (Takabatake et al., 1999). 2.3 Known expression patterns and regulation When and where the corn phosphate transporter plays a role is not fixed. Many PHT1 genes, such as ZmPHT1; 2, 4, 6, 7, 9, 11 are activated at low phosphorus levels, and some also show elevated expression when cooperating with arbuscular mycorrhizal fungi (Liu et al., 2018). However, there are exceptions, such as ZmPHT1; Its regulatory methods under certain conditions are slightly different from those of other members. The expression of these genes also varies in different tissues. Some are highly expressed only in pollen or mycorrhizal tissues, while others are related to the re-transport of phosphorus in buds (Nagy et al., 2006). In addition, promoter sequence analysis has discovered many cis-regulatory elements that respond to phosphorus starvation or mycorrhizal signals (Li et al., 2020), which further indicates that the regulatory system is very complex. The behavior of the SPX gene is also typical. They are also easily induced under phosphorus deficiency conditions, demonstrating the high regulatory nature of corn in phosphorus management (Figure 1). 3 Functional Roles of Maize Phosphate Transporters 3.1 Uptake of phosphate from soil under varying environmental conditions Sometimes, there is not much phosphorus in the soil, and at such times, plants have to find ways to absorb it more efficiently. Corn can achieve this mainly through some phosphate transporters, especially members of the PHT1 family like ZmPT7 and ZmPt9. Proteins like ZmPT7 are expressed in both roots and leaves, especially when there is a phosphorus deficiency, they are significantly activated, enhancing the plant's ability to absorb phosphorus. And for instance, ZmPt9 can only take effect after partnering with arbuscular mycorrhizal fungi. This type of fungus has a higher colonization rate in low-phosphorus environments. They can help corn absorb the phosphorus that was otherwise difficult to obtain. Therefore, these transport proteins not only have strong adaptability but also can "adjust strategies" according to soil conditions, helping plants improve nutrient utilization efficiency.
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