Role of Two Transcription Factors (TGA 1a and TGA 2.1) in the Mi-1-Mediated Resistance of Tomato to the Root-Knot Nematode Meloidogyne java']javanica

The Mi-1 gene in tomato confers resistance against insects and nematodes. The mechanisms involved in the functioning of this gene are not completely known, and they differ depending on the damaging organism (insect or nematode). Transcription factors (TF) from different families are essential for plant defence, and the TGAs, members of the Basic Leucine Zipper (bZIP) TF family, are relevant in different pathosystems. In this work, the implication of TGA 1a and TGA 2.1 genes in Mi-1 resistance against the root-knot nematode Meloidogyne javanica was studied, by virus-induced gene silencing (VIGS) based on Tobacco rattle virus (TRV). Results showed that infiltration with the empty TRV vector did not alter Mi-1-mediated resistance, confirming the adequacy of this method. Silencing of the TGA 1a gene resulted in a decrease in resistance to M. javanica, as the numbers of egg masses were significantly higher than those on non-silenced plants. This decrease in resistance was similar to that caused by silencing the Mi-1 gene. However, the silencing of the TGA 2.1 gene caused a limited loss of resistance, with infestation levels intermediate between those of resistant and susceptible varieties. Thus, our results demonstrate the requirement of TGA 1a in Mi-1-mediated resistance to M. javanica, while the incomplete silencing of TGA 2.1 impaired a specific determination of its role.