On the role of a Lipid-Transfer Protein. Arabidopsis ltp3 mutant is compromised in germination and seedling growth

Abstract

Plant Lipid-Transfer Proteins (LTPs) exhibit the ability to reversibly bind/transport lipids in vitro. LTPs have been involved in diverse physiological processes but conclusive evidence on their role has only been presented for a few members, none of them related to seed physiology. Arabidopsis seeds rely on storage oil breakdown to supply carbon skeletons and energy for seedling growth. Here, Arabidopsis ltp3 mutant was analyzed for its ability to germinate and for seedling establishment. Ltp3 showed delayed germination and reduced germination frequency. Seedling growth appeared reduced in the mutant but this growth restriction was rescued by the addition of an exogenous carbon supply, suggesting a defective oil mobilization. Lipid breakdown analysis during seedling growth revealed a differential profile in the mutant compared to the wild type. The involvement of LTP3 in germination and seedling growth and its relationship with the lipid transfer ability of this protein is discussed.

Keywords: lipid transfer protein; oilseed; seed germination; seedling growth.

Figure 1.

Amino acidic and genomic structure of Arabidopsis thaliana LTP3 (A) LTP3 amino acid sequence (Uniprot Q9LLR7). (B) Schematic representation of ltp3 insertion line genomic structure (SALK 095248). Exons, untranscribed regions, and intron, are indicated by gray boxes, white boxes, and lines, respectively. The T-DNA insertion in ltp3 mutant is shown.

Figure 2.

Germination is impaired in Atltp3. Seeds of wild type (black square) and ltp3 (black triangle) lines were sown and allowed to germinate on MS media with vitamins in growth chamber with 16 h daily illumination at 25°C. Radicle protrusion was assessed in more than 40 seeds per batch, at different times after sowing. Error bars represent SD. A Two-way ANOVA and Bonferroni posttests was calculated at the probability of either 5% (*P < 0.05), 1% (**P < 0.01) or 0.1% (***P < 0.001).

Figure 3.

Postgerminative growth is reduced in Atltp3. (A) Wild-type and ltp3 seedlings dark-grown on agar plates containing MS medium plus or minus 1% sucrose. Representative photograph taken 7 d after stratification. Bar: 1 cm. (B) Hypocotyl length in wild-type (white bars) and ltp3 (black bars) seedlings. Error bars represent SD. A one-way ANOVA and Tukey's Multiple Comparison posttests was calculated at the probability of 0.1% (***P < 0.001).

Figure 4.

Fatty acid mobilization is altered in Atltp3. TAG-derived fatty acid profile in wild type (black bars) and ltp3 (white bars) during germination. (A) Seeds, 0 das; (B) Seedlings , 5 das. Data are mean ± SD for n = 3 (wt) or 5 (ltp3).