Short Peptides Induce Development of Root Hair Nicotiana tabacum

Abstract

Root hairs absorb soil nutrients and water, and anchor the plant in the soil. Treatment of tobacco (Nicotiana tabacum) roots with glycine (Gly) amino acid, and glycilglycine (GlyGly) and glycilaspartic acid (GlyAsp) dipeptides (10^-7 M concentration) significantly increased the development of root hairs. In the root, peptide accumulation was tissue-specific, with predominant localization to the root cap, meristem, elongation zone, and absorption zone. Peptides penetrated the epidermal and cortical cell and showed greater localization to the nucleus than to the cytoplasm. Compared with the control, tobacco plants grown in the presence of Gly, GlyGly, and GlyAsp exhibited the activation of WER, CPC, bHLH54, and bHLH66 genes and suppression of GTL1 and GL2 genes during root hair lengthening. Although Gly, GlyGly, and GlyAsp have a similar structure, the mechanism of regulation of root hair growth in each case were different, and these differences are most likely due to the fact that neutral Gly and GlyGly and negatively charged GlyAsp bind to different motives of functionally important proteins. Short peptides site-specifically interact with DNA, and histones. The molecular mechanisms underlying the effect of exogenous peptides on cellular processes remain unclear. Since these compounds acted at low concentrations, gene expression regulation by short peptides is most likely of epigenetic nature.

Keywords: Nicotiana tabacum L.; root hairs; short peptides.

Figure 1

Tobacco seedlings grown on Murashige and Skoog (MS) medium supplemented with or without Gly amino acid and GlyGly and GlyAsp dipeptides.

Figure 2

Visualization of FITC-labeled Gly and dipeptides in tobacco seedling roots. (a–c) Control roots. (d–f) Roots incubated with FITC. (g–i) Roots incubated with FITC-Gly. (j–l) Roots incubated with FITC-GlyGly. (m–o) Roots incubated with FITC-GlyAsp. Scale = 200 µm. (c,f,i,l,o) Semi-thin root sections. Arrows point to cw—cell wall; cp—cytoplasm, nu—nuclei.

Figure 3

Effect of peptides on the length, density, and pubescence of root hairs of tobacco seedlings. 1—control; 2—Gly; 3—GlyGly; 4—GlyAsp. Scale = 1000 µm. The mean values (n = 20) and their standard deviations are shown according to significant value, p < 0.05. Different letters above the bars indicate significantly different values.

Figure 4

Relative expression levels of genes in tobacco seedling roots. 1—control; 2—Gly; 3—GlyGly; and 4—GlyAsp. Data represent mean ± standard deviation. The diagram below indicates the activation or repression of genes in the presence of Gly and dipeptides. Standard deviations are shown according to significant value, p < 0.05. Different letters above the bars indicate significantly different values.