Gene Editing Boosts Tomato Resistance to Mildew with Minimal Downsides

Jenn Hoskins
10th August, 2024

Gene Editing Boosts Tomato Resistance to Mildew with Minimal Downsides

Homozygous knockout dnd1 mutants (E1, E4) in tomato (Solanum lycopersicum) exhibit severe dwarfism and early auto-necrosis (a, b), whereas the E3 mutant harboring a 3-amino-acid deletion displays near-normal height with minimal necrotic symptoms (c), demonstrating that specific DND1 mutations can confer powdery mildew resistance with substantially reduced fitness costs.

Image adapted from: Li et al. / CC BY (Source)

Key Findings

  • Researchers at the University of Torino used CRISPR-Cas9 to target the DND1 gene in tomatoes to enhance resistance to powdery mildew
  • The E3 mutant tomato plants showed normal growth and fewer disease symptoms, unlike other mutants which had growth issues
  • The E3 mutation did not introduce foreign DNA, making it a precise and promising method for breeding disease-resistant tomatoes
Powdery mildew (PM), caused by the fungal pathogen Oidium neolycopersici, poses a significant threat to tomato crops (Solanum lycopersicum L.), affecting their productivity and quality[1]. This study, conducted by researchers at the University of Torino, investigates a novel approach to enhancing tomato resistance to PM by targeting the Defense No Death 1 (DND1) gene using CRISPR-Cas9 technology. Previous research has established that plants possess various resistance mechanisms against pathogens, including fungi like powdery mildew. These pathogens, however, have evolved sophisticated strategies to overcome plant defenses[2]. Specifically, the MLO (Mildew Locus O) gene family has been identified as a key player in plant susceptibility to powdery mildew. For instance, the loss-of-function of the MLO gene SlMLO1 in tomatoes leads to a form of resistance characterized by the formation of papillae, which block fungal penetration[3][4]. In this new study, the researchers aimed to disrupt the function of the DND1 gene to enhance resistance to PM while minimizing negative effects on plant health. The DND1 gene, when mutated, has been shown to increase plant resilience against various pathogens, but at the cost of reduced plant vigor and health. To address this, the team designed a CRISPR-Cas9 construct targeting three exons of the SlDND1 gene and introduced it into the tomato variety Moneymaker (MM) through Agrobacterium tumefaciens-mediated transformation. Three T1 lines (E1, E3, and E4) were generated and crossed with MM, followed by self-pollination to produce TF2 families. The researchers observed that all TF2 plants homozygous for the dnd1 mutation (dnd1/dnd1) exhibited significantly reduced PM symptoms compared to heterozygous (DND1/dnd1) and wild-type (DND1/DND1) plants. Among the knockout (KO) mutants, E1 and E4 showed dwarfism and auto-necrosis, whereas E3, which had deletions of only three amino acids, displayed normal growth and fewer auto-necrotic spots. The analysis of the 3D structures of the reference and mutant DND1 proteins revealed substantial conformational changes in the protein derived from E3, suggesting that these structural alterations might influence its function. Whole-genome sequencing of the E3 line confirmed the absence of off-target mutations and the segregation of the Cas9 gene, ensuring that the mutation was precise and did not introduce foreign DNA. This study builds on previous findings that highlight the role of susceptibility genes in plant-pathogen interactions. For example, the SlMLO1 gene in tomatoes has been extensively studied, and its disruption has been shown to confer resistance to powdery mildew[3][4]. Similarly, genome editing technologies like CRISPR/Cas9 have demonstrated the potential to create resistant plant varieties without introducing foreign DNA, as seen in the development of the Tomelo tomato variety[5]. By targeting the DND1 gene, the researchers have confirmed its role as a susceptibility gene in tomatoes. The E3 mutant allele, in particular, offers a promising avenue for breeding PM-resistant tomatoes without compromising plant fitness. This study not only advances our understanding of the genetic basis of disease resistance in tomatoes but also provides a practical approach to developing robust, disease-resistant crops through precise genome editing.

BiotechGeneticsPlant Science

References

Main Study

1) Less is more: CRISPR/Cas9-based mutations in DND1 gene enhance tomato resistance to powdery mildew with low fitness costs.

Published 10th August, 2024

https://doi.org/10.1186/s12870-024-05428-3

Related Studies

2) Powdery mildew susceptibility and biotrophic infection strategies.

Journal: FEMS microbiology letters, Issue: Vol 245, Issue 1, Apr 2005

3) Genome-Wide Study of the Tomato SlMLO Gene Family and Its Functional Characterization in Response to the Powdery Mildew Fungus Oidium neolycopersici.

https://doi.org/10.3389/fpls.2016.00380

4) Discovery and Characterization of a Novel Tomato mlo Mutant from an EMS Mutagenized Micro-Tom Population.

https://doi.org/10.3390/genes12050719

5) Rapid generation of a transgene-free powdery mildew resistant tomato by genome deletion.

https://doi.org/10.1038/s41598-017-00578-x


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