Overexpression of Cassava MeSTP7 Promotes Arabidopsis Seedling Development

Abstract

The sugar transporter (STP) gene family is a key regulator of plant development, which is crucial for the efficient transport and utilization of sugars during plant growth and development. In this study, we identified the MeSTP7 gene, which is highly expressed in cassava fibrous roots, early storage roots, and under hormonal treatment, including IAA, MeJA, ABA, and GA₃, and abiotic stressors, such as mannitol and NaCl. A strong response was observed with exoqenous IAA. Transfecting MeSTP7 into Arabidopsis promoted early seedling growth, particularly in lateral root development. The content of endogenous hormones (IAA and MeJA) as well as soluble sugars (sucrose, fructose, and glucose) was elevated in transgenic Arabidopsis. Hormone treatments with IAA, MeJA, GA₃, and ABA on transgenic Arabidopsis revealed that transgenic Arabidopsis responded positively to added 20 μM IAA. They also exhibited co-induced regulation of lateral root formation by GA₃, MeJA, and ABA. qRT-PCR analysis showed that overexpression of MeSTP7 upregulated the expression of IAA14, ARF7, and ARF19 in Arabidopsis. Under IAA treatment, the expression of these genes was similarly upregulated but downregulated under MeJA treatment. These results suggest that MeSTP7 may promote Arabidopsis seedling development by increasing the content of sucrose, glucose, and fructose in roots, which in turn influences IAA-based hormonal signaling.

Keywords: MeSTP7; cassava; hormone treatment; sugar transporter protein; transgenic Arabidopsis.

Figure 1

Expression analysis of the MeSTP7 gene in cassava tissues. The storage roots were selected from cassava roots that had grown for 80 days. MeTubulin and MeActin were used as internal controls. The expression level of young leaves was set to 1. The data represent the mean ± standard deviation of three biological replicates. Different lowercase letters indicate significant differences (p < 0.05).

Figure 2

The root expression pattern of the MeSTP7 gene under various treatments of cassava seedlings, including drought, salt, IAA, MeJA, ABA, and GA₃. The treatment methods were as follows: gibberellin treatment was 100 μM GA₃; IAA treatment was treated with 100 μM IAA; ABA treatment was 100 μM ABA; MeJA treatment was 100 μM MeJA; salt stress was 300 mM NaCl; the drought treatment was simulated by 100 mM mannitol. The MeTubulin gene and MeActin gene were normalized as an internal control. The relative expression value of the control sample was standardized to the control value 1. The data are expressed as the average of three independent organisms. Different lowercase letters indicate significant differences (p < 0.05).

Figure 3

Detection of transgenic Arabidopsis expressing heterologous MeSTP7. (a) A schematic diagram of the pCAMBIA1300-MeSTP7: GFP recombinant vector. (b) PCR detection of the leaves of resistant transgenic Arabidopsis seedlings that survived on 1/2 MS medium supplemented with 100 mg/L hygromycin, T1 generation. M: DL2000; P: Positive plasmid control; 1–18: Transgenic Arabidopsis lines; WT: Columbia-0 Arabidopsis. (c) Expression of the MeSTP7 gene in selected transgenic lines. The expression of OE8 was set to 1, and the AtActin gene was normalized as an internal control. (d) Expression of GFP in T3 transgenic lines was observed using a Luyor-3415RG dual-wavelength fluorescent protein excitation light source.

Figure 4

MeSTP7 increases the levels of IAA, MeJA, sucrose, glucose, and fructose in Arabidopsis seedlings, promoting seedling growth. (a) Transgenic MeSTP7 and WT plants were grown on 1/2 MS agar for 7 days. (b) Statistical analysis of plant root fresh weight. (c) Statistical analysis of the number of plant lateral roots. (d) The endogenous IAA content in the roots of the plants was measured. (e) The endogenous MeJA content in the roots of the plants was measured. (f) The content of glucose, fructose, and sucrose in WT and MeSTP7-overexpression Arabidopsis plants grown in 1/2 MS medium. The data were expressed as the mean ± SEM of three biological replicates. * represents a significant difference (p < 0.05), ** represents a highly significant difference (p < 0.01).

Figure 5

IAA treatment enhances root development in Arabidopsis with MeSTP7 overexpression. (a) Phenotype of transgenic Arabidopsis under different IAA concentration gradients. (b) The total plant fresh weight and root fresh weight of Arabidopsis under different IAA concentration gradient treatments. (c) Expression of root development-related genes under different IAA concentrations. * represents a significant difference (p < 0.05), ** represents a highly significant difference (p < 0.01).

Figure 6

MeJA treatment inhibited the formation of lateral roots in MeSTP7-overexpressing Arabidopsis plants. (a) Phenotypes of transgenic Arabidopsis under different MeJA concentration gradients. (b) Fresh weight and lateral root number of transgenic Arabidopsis under different MeJA concentration gradients. (c) Expression of root development-related genes under different MeJA concentrations. * represents a significant difference (p < 0.05), ** represents a highly significant difference (p < 0.01).