Signaling in the Tomato Immunity against Fusarium oxysporum

Abstract

New strategies of control need to be developed with the aim of economic and environmental sustainability in plant and crop protection. Metabolomics is an excellent platform for both understanding the complex plant-pathogen interactions and unraveling new chemical control strategies. GC-MS-based metabolomics, along with a phytohormone analysis of a compatible and incompatible interaction between tomato plants and Fusarium oxysporum f. sp. lycopersici, revealed the specific volatile chemical composition and the plant signals associated with them. The susceptible tomato plants were characterized by the over-emission of methyl- and ethyl-salicylate as well as some fatty acid derivatives, along with an activation of salicylic acid and abscisic acid signaling. In contrast, terpenoids, benzenoids, and 2-ethylhexanoic acid were differentially emitted by plants undergoing an incompatible interaction, together with the activation of the jasmonic acid (JA) pathway. In accordance with this response, a higher expression of several genes participating in the biosynthesis of these volatiles, such as MTS1, TomloxC,TomloxD, and AOS, as well as JAZ7, a JA marker gene, was found to be induced by the fungus in these resistant plants. The characterized metabolome of the immune tomato plants could lead to the development of new resistance inducers against Fusarium wilt treatment.

Keywords: Fusarium; GC-MS; biotic interaction; metabolomics; natural products; tomato; volatiles.

Figure 1

Fusarium wilt symptoms in Momor (MOM) and Movione (MOV) tomato plants at 14 dpi after Fusarium oxysporum f. sp. lycopersici (Fol) inoculation. Tomato plants display the representative phenotype observed in infected susceptible MOM (B) compared to mock-inoculated (A), and infection-resistant MOV (D), as compared to their corresponding mock-inoculated (C).

Figure 2

Logarithm of the ratios of the relative expression levels of PR1 (A), JAZ7 (B), ACS2 (C), and LEA (D) between Fol-inoculated and mock-inoculated susceptible Momor (MOM, white) and resistant Movione (MOV, gray) tomato plants upon Fusarium oxysporum f. sp. lycopersici infection at 3, 7, and 14 dpi by RT-qPCR. Values obtained were normalized in relation to the elongation factor 1 α (accession X53043.1). cDNA expression levels were expressed as the average log(ratio) values of a representative experiment. Asterisks (*) point out statistical differences between mock-inoculated and Fol-inoculated MOM and MOV plants according to t-test or Mann–Whitney test, with p < 0.05 (*), p < 0.01 (**), and p < 0.001 (***).

Figure 3

Logarithm of the ratios of the SA (A), JA (B) and ABA (C) phytohormone levels in susceptible Momor (MOM; white) and resistant Movione (MOV; gray) tomato plants upon Fusarium oxysporum f. sp. lycopersici inoculation at 3, 7 and 14 dpi, with respect to the corresponding mock-inoculated plants. Values were expressed as the average log(ratio) of data corresponding to a representative experiment. Asterisks (*) point out statistical differences according to t-test or a Mann–Whitney test, with p < 0.05 (*), p < 0.01 (**) and p < 0.001 (***).

Figure 4

Score plot of the PCA based on the whole array of the mass spectra within an m/z range from 35 to 250. VOCs were analyzed from susceptible Momor (MOM; white) and resistant Movione (MOV; gray) tomato plants infected by Fusarium oxysporum f. sp. lycopersici at 7 and 14 dpi. PC1 and PC2 explain the 19% and 12% of variance separating the samples according to the type of interaction and timing of the fungal infection, respectively. Statistically differential metabolites according to t-test for both incompatible (MOV/MOM ratio ≥ 1.7) and compatible (MOV/MOM ratio ≤ 0.8) interactions are shown in boxes.

Figure 5

Logarithm of the ratios of the relative expression levels between Fol-infected and mock-inoculated leaves of TomloxC (A), TomloxA (B), TomloxD (C), TomloxF (D), HPL (E), AOS (F), MTS1 (G), and SAMT1 (H) in susceptible Momor (MOM; white) and resistant Movione (MOV; gray) tomato plants upon Fusarium oxysporum f. sp. lycopersici infection at 3 dpi and 7 dpi by RT-qPCR. cDNA expression levels were expressed as the average log(ratio) values of a representative experiment. Values were expressed in relation to the endogenous gene, elongation factor 1 α. Statistical analysis was done by means of a t-test or a Mann–Whitney test. Asterisks (*) mean p < 0.05 (*), p < 0.01 (**), and p < 0.001 (***).