Abstract
Although production of tomato (Solanum lycopersicum) is threatened by a number of major diseases worldwide, it has been difficult to identify effective and durable management measures against these diseases. In this study, we attempted to improve tomato disease resistance by transgenic overexpression of genes encoding the Arabidopsis thaliana Elongator (AtELP) complex subunits AtELP3 and AtELP4. We show that overexpression of AtELP3 and AtELP4 significantly enhanced resistance to tomato bacterial speck caused by the Pseudomonas syringae pv. tomato strain J4 (Pst J4) without clear detrimental effects on plant growth and development. Interestingly, the transgenic plants exhibited resistance to Pst J4 only when inoculated through foliar sprays but not through infiltration into the leaf apoplast. Although this result suggested possible involvement of stomatal immunity, we found that Pst J4 inoculation did not induce stomatal closure and there were no differences in stomatal apertures and conductance between the transgenic and control plants. Further RNA sequencing and real-time quantitative PCR analyses revealed a group of defense-related genes to be induced to higher levels after infection in the AtELP4 transgenic tomato plants than in the control, suggesting that the enhanced disease resistance of the transgenic plants may be attributed to elevated induction of defense responses. Additionally, we show that the tomato genome contains single-copy genes encoding all six Elongator subunits (SlELPs), which share high identities with the AtELP proteins, and that SlELP3 and SlELP4 complemented the Arabidopsis Atelp3 and Atelp4 mutants, respectively, indicating that the function of tomato Elongator is probably conserved. Taken together, our results not only shed new light on the tomato Elongator complex, but also revealed potential candidate genes for engineering disease resistance in tomato.
Highlights
Tomato (Solanum lycopersicum) fruit was once thought to be poisonous, but since being integrated as part of the human diet, its popularity and consumption have increased over the years
We show that overexpression of AtELP3 and AtELP4 significantly enhanced resistance to tomato bacterial speck caused by the P. syringae pv. tomato strain J4 (Pst J4) without clear detrimental effects on plant growth and development
Based on PCR amplification of the cDNA of AtELP3 or AtELP4 using gene specific primers (Supplementary Table S1), out of 80 T1 putative transgenic plants produced by the University of Nebraska–Lincoln (UNL) Plant Transformation Facility, 36 carried the AtELP3 transgene and 35 the AtELP4 gene
Summary
Tomato (Solanum lycopersicum) fruit was once thought to be poisonous, but since being integrated as part of the human diet, its popularity and consumption have increased over the years. Tomato production has an economic impact worldwide, but it is a costly crop to produce. It is a labor-intensive crop that requires significant amount of chemical inputs to be protected from a Overexpression of Elongator Subunits in Tomato wide variety of pests and diseases. There are a number of diseases that affect tomatoes, including bacterial speck, which is caused by the bacterial pathogen Pseudomonas syringae pv. Bacterial speck can cause up to 75% losses in yield, if present early in the production cycle (Yunis et al, 1980). Pathogen-free seeds and resistant varieties carrying the resistance (R) gene Pto have been implemented to control the disease (Monroe and Sasser, 1980; Pedley and Martin, 2003). P. syringae pv. tomato strains have evolved to overcome the R gene-mediated resistance in tomato (Thapa and Coaker, 2016)
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