Abstract
Eggplant (Solanum melongena L.) is one of the most important vegetables among the Solanaceae and can be a host to fungal species causing powdery mildew (PM) disease. Specific homologs of the plant Mildew Locus O (MLO) gene family are PM susceptibility factors, as their loss of function results in a recessive form of resistance known as mlo resistance. In a previous work, we isolated the eggplant MLO homolog SmMLO1. SmMLO1 is closely related to MLO susceptibility genes characterized in other plant species. However, it displays a peculiar non-synonymous substitution that leads to a T → M amino acid change at protein position 422, in correspondence of the MLO calmodulin-binding domain. In this study, we performed the functional characterization of SmMLO1. Transgenic overexpression of SmMLO1 in a tomato mlo mutant compromised resistance to the tomato PM pathogen Oidium neolycopersici, thus indicating that SmMLO1 is a PM susceptibility factor in eggplant. PM susceptibility was also restored by the transgenic expression of a synthetic gene, named s-SmMLO1, encoding a protein identical to SmMLO1, except for the presence of T at position 422. This indicates that the T → M polymorphism does not affect the protein role as PM susceptibility factor. Overall, the results of this work are of interest for the functional characterization of MLO proteins and the introduction of PM resistance in eggplant using reverse genetics.
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Acknowledgements
This work was supported by the Italian Ministry of University and Research through the project GenHort PON R&C, and internal funding of Wageningen UR Plant Breeding.
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Valentina Bracuto and Michela Appiano have contributed equally to this work.
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Supplementary Fig. S1
Relative quantification of SmMLO1 expression levels in: eight T1 individuals transformed with SmMLO1 (T1_J, T1_K, T1_L, T1_M, T1_N, T1_O, T1_P and T1_Q); nine T1 individuals transformed with a synthetic gene (s-SmMLO1) identical to SmMLO1 except for encoding a M → T substitution at position 422 (T1_A, T1_B, T1_C, T1_D, T1_E, T1_F, T1_G, T1_H and T1_I); the tomato line Slmlo1, used as background for transformation. (TIFF 416 kb)
Supplementary Fig. S2
Results of a second experimental trial aiming to assess the effects of the transgenic expression of SmMLO1 in a tomato mlo loss-of-function genetic background. A) Average disease index (DI) recorded fifteen days after artificial inoculation with the PM fungus Oidium neolycopersici. The graph refers to: transgenic T2 individuals of three independent families (T2_M, T2_Q and T2_P) transformed with SmMLO1; transgenic T2 individuals of three independent families (T2_E, T2_F and T2_I) transformed with the synthetic gene s-SmMLO1; the commercial cultivar Moneymaker (MM); the line Slmlo1, used as background for transformation). The scale from 0 (completely resistant) to 3 (fully susceptible) reported by Bai et al. (2008), was used for scoring. Bars refer to standard errors of at least six replicates. Different letters indicate significant differences among the treatments, inferred by the Tukey test (P < 0.05). B) Phenotype of selected transgenic individuals of the lines T2_E, T2_F and T2_M, a non-transgenic individual of the line T2(-)_M, a MM individual and an individual of the line Slmlo1. (TIFF 2408 kb)
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Bracuto, V., Appiano, M., Ricciardi, L. et al. Functional characterization of the powdery mildew susceptibility gene SmMLO1 in eggplant (Solanum melongena L.). Transgenic Res 26, 323–330 (2017). https://doi.org/10.1007/s11248-016-0007-9
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DOI: https://doi.org/10.1007/s11248-016-0007-9