GA3-Induced SlXTH19 Expression Enhances Cell Wall Remodeling and Plant Height in Tomatoes

Abstract

Plant height represents a pivotal agronomic trait for the genetic enhancement of crops. The plant cell wall, being a dynamic entity, is crucial in determining plant stature; however, the regulatory mechanisms underlying cell wall remodeling remain inadequately elucidated. This study demonstrates that the application of gibberellin 3 (GA3) enhances both plant height and cell wall remodeling in tomato (Solanum lycopersicum L.) plants. RNA sequencing (RNA-seq) results of GA3 treatment showed that the DEGs were mostly enriched for cell wall-related pathways; specifically, GA3 treatment elicited the expression of the cell wall-associated gene XYLOGLUCAN ENDOTRANSGLUCOSYLASE/HYDROLASE 19 (SlXTH19), whose overexpression resulted in increased plant height. Comparative analyses revealed that SlXTH19-overexpressing lines exhibited larger cell dimensions and increased XTH activity, along with higher contents of lignin, cellulose, and hemicellulose, thereby underscoring the gene's role in maintaining cell wall integrity. Conversely, treatments with ethephon (ETH) and 1-Naphthaleneacetic acid (NAA) led to suppressed plant height and reduced SlXTH19 expression. Collectively, these findings illuminate a competitive interplay between GA and ethylene/auxin signaling pathways in regulating cell wall remodeling via SlXTH19 activation, ultimately influencing tomato plant height.

Keywords: GA; SlXTH19; cell wall; plant height; tomato.

Figure 1

JZ34 seedlings have a taller phenotype than JZ18 seedlings. (A) Phenotypes of JZ34 and JZ18 at 30 d, 36 d, 42 d, and 48 d after seed breaking. Scale bars, 8 cm. (B) Plant height, hypocotyl length, and epicotyl length of 30-day-old JZ34 and JZ18 plants. (C) Plant heights of the JZ34 and JZ18 plants during different development stages. (D) Internode lengths of 30-day-old JZ34 and JZ18 plants. (E) Phenotypes of JZ34 and JZ18 plants sprayed with different concentrations of exogenous GA and paclobutrazol (PAC) for 9 d. Scale bars, 6 cm. (F) Plant heights of JZ34 and JZ18 plants after GA treatment for 9 d. (G) Plant heights of JZ34 and JZ18 plants after PAC treatment for 9 d. (H) Plant heights of JZ34 and JZ18 plants after PAC treatment for 18 d. Values represent the means ± SD, n = 3 pools, with 5 plants per pool. Student’s t-test was performed for (B,C); asterisks indicate significant differences compared with JZ34 (#) at ** p < 0.01. Different letters indicate significant differences (p < 0.05) according to Duncan’s test for (F–H).

Figure 2

GA regulates XTH gene expression in tomato stems. (A–D) Gene ontology (GO) enrichment pathway scatterplot for the differentially expressed genes (DEGs) in JZ18 vs. JZ34, JZ18 vs. JZ18 GA, JZ34 vs. JZ34 GA, and JZ18 GA vs. JZ34 GA comparisons. DEGs screened with |log2(FC)| ≥ 1.0, p < 0.05, and a false discovery rate (FDR) < 0.05 among four pairwise comparisons. The blue boxes represent cell wall-related pathways and the red boxes represent ethylene and auxin-related pathways. (E–H) XTH activity and (E) lignin (F), cellulose, and (G) hemicellulose contents (H) in JZ34 and JZ18 without and with GA treatment. Values represent means ± SD, n = 3 pools, with 5 plants per pool. Different letters indicate significant differences (p < 0.05) according to Duncan’s test.

Figure 3

GA regulates XTH gene expression in tomato stems. (A) Heatmap representation of the expression of 26 candidate SlXTH genes. The red box represents the most significant difference. (B) Phylogenetic tree of XTH family members from Solanum lycopersicum and Arabidopsis thaliana. The red dot represents the SlXTH19. (C) Relative expression of SlXTH19 in JZ34 (A) and JZ18 (B) plants under GA treatment for 9 d. (D) Relative expression of SlXTH19 in JZ34 and JZ18 5 d, 10 d, 15 d, 20 d, and 25 d after seed breaking. (E) Tissue-specific expression of SlXTH19. (F) SlXTH19-GFP is localized to the plasma membrane of Nicotiana benthamiana cells. An mCherry-labeled plasma membrane marker (AtCBL1) was coexpressed to visualize the plasma membrane. Values represent means ± SD, n = 3 pools, with 5 plants per pool. Different letters indicate significant differences (p < 0.05) according to Duncan’s test.

Figure 4

Overexpression of SlXTH19 promotes tomato plant height. (A) Phenotypes of wild-type (JZ34 and JZ18) and SlXTH19-overexpressing transgenic plants are shown. Scale bars, 8 cm. (B,C) Relative expression of SlXTH19 in SlXTH19-OE-JZ34 lines (B) and SlXTH19-OE-JZ18 lines (C). Values represent the means ± SD, n = 3 pools, with 5 plants per pool. Student’s t-test was performed; asterisks indicate significant differences compared with JZ34 and JZ18 (#) at ** p < 0.05, respectively. (D–F) Plant heights, hypocotyl lengths, and stem diameters of the plants shown in (A). Values represent means ± SD, n = 3 pools, with 5 plants per pool. Different letters indicate significant differences (p < 0.05) according to Duncan’s test.

Figure 5

Overexpression of SlXTH19 promotes tomato plant height by increasing cell length. (A) Images depicting photographs of the stem cells of different genotypes of SlXTH19-OE and wild-type (JZ34 and JZ18). Scale bars, 50 μm. (B,C) Stem cell length and cell size in the stems of SlXTH19-OE and wild-type (JZ34 and JZ18). The values represent the means ± SD, n = 3 pools, with 10 plants per pool. Different letters indicate significant differences (p < 0.05) according to Duncan’s test.

Figure 6

XTH activity and lignin, cellulose, and hemicellulose contents in SlXTH19-OE and wild-type (JZ34 and JZ18). The graph displays XTH activity (A), lignin content (B), cellulose content (C), and hemicellulose content (D) in both SlXTH19-OE and wild-type (JZ34 and JZ18). Values represent means ± SD, n = 3 pools, with 5 plants per pool. Different letters indicate significant differences (p < 0.05) according to Duncan’s test.

Figure 7

Effects of ETH, GA, and NAA treatments on plant height. (A) Phenotypes of JZ18 and JZ34 under ETH, GA, and NAA treatment for 20 d. (B,C) The plant heights of plants shown in (A). Scale bars, 8 cm. (D) Relative expression of SlXTH19 under ETH and NAA treatments for 20 d. GA: 0.05 mM; ETH: 1 mM; NAA: 100 μM. The values represent the means ± SD, n = 3 pools, with 10 plants per pool. Different letters indicate significant differences (p < 0.05) according to Duncan’s test.