Newly identified gene grants tomatoes resistance to bacterial speck
disease
Researchers are working to create tomatoes that are protected from a devastating disease

Date:
September 2, 2020
Source:
Boyce Thompson Institute
Summary:
Bacterial speck disease, which reduces both fruit yield and
quality, has been a growing problem in tomatoes over the last
five years. Because the culpable bacterium, Pseudomonas syringae,
prefers a cool and wet climate, crops in places such as New York
State have been particularly susceptible. Researchers have uncovered
the first known gene to impart resistance to a particular strain
of the bacterium that causes speck disease.



FULL STORY ========================================================================== Bacterial speck disease, which reduces both fruit yield and quality, has
been a growing problem in tomatoes over the last five years. Because the culpable bacterium, Pseudomonas syringae, prefers a cool and wet climate,
crops in places such as New York State have been particularly susceptible.


========================================================================== Recent research at the Boyce Thompson Institute headed by postgraduates Carolina Mazo-Molina and Samantha Mainiero and overseen by faculty
member Greg Martin may change this. Published in the August issue of The
Plant Journal, their work has uncovered the first known gene to impart resistance to a particular strain, called "race 1," of the bacterium
causing speck disease.

Another resistance gene, Pto, which provides resistance to race 0 strains
of Pseudomonas syringae, has been used for over 25 years. However,
crops remain vulnerable to the increasingly common race 1 strain,
resulting in significant losses for growers.

With the discovery of this new gene, which the researchers have dubbed Pseudomonas tomato race 1 (Ptr1), damage caused by bacterial speck
disease may soon become a thing of the past.

"We are working with plant breeders now to introduce the Ptr1 gene into
tomato varieties that already have Pto," explains Martin, who is also a professor at Cornell University's School of Integrative Plant Science. "If
you do that, then you will have resistance to all known bacteria that
cause speck disease." Natural Selection and Serendipity The project
started in 2015, after a chance outbreak of bacterial speck disease at
one of Cornell's research farms, where BTI faculty member Jim Giovannoni
was researching tomato fruit quality. Giovannoni is also a USDA scientist
and an Adjunct Professor in Cornell's School of Integrative Plant Science.



========================================================================== "Speck disease wiped out their entire trial except for two plants,"
explains Martin. "Both of those plants turned out to have the Ptr1
resistance gene. This was a remarkable coincidence of natural selection
and serendipity." The two plants that survived both contained a gene
derived from Solanum lycopersicoides, a wild relative of the cultivated
tomato. By collecting seeds of the plants and studying their inheritance patterns, the team determined that a single region on one chromosome
is responsible for conferring resistance, work that was published in
Molecular Plant-Microbe Interactions in 2019. In this most recent paper,
they have identified a specific gene in this region that confers race
1 resistance, the Ptr1 gene.

Mazo-Molina described the thrill of identifying the gene. "When we
found Ptr1, I would always say it 'might be the gene' or 'could be the
gene,'" she explains. "But at some point, I was able to tell myself,
'This is the gene. You don't have to doubt it.'" Ptr1 codes for a
protein that indirectly detects the presence of a pathogenic protein
called AvrRpt2. Both apple and the popular model plant Arabidopsis have
genes that encode proteins that also recognize the same bacterial protein.

"The three proteins are completely different," says Martin. "There's
no similarity at all. It looks like an example of convergent evolution, independent solutions in different plants to the same problem." "Because detection of AvrRpt2 evolved multiple times across evolutionary history,
the AvrRpt2 protein likely plays a key role in the pathogen's ability
to infect plants," Martin says.



==========================================================================
Next Steps Now that the gene has been identified, the team is focused on developing tomato varieties that carry the Ptr1 gene. "The wild species
in which Ptr1 is naturally found is really difficult to cross with
cultivated tomatoes," explains Mainiero. "We can't just use traditional breeding methods." Thankfully, there may be another way.

"A defective form of the gene is present in many tomato varieties
already," says Martin, "with natural mutations having made it
nonfunctional. There is a new type of gene editing technology called
CRISPR Prime Editing that might allow us to go in and repair this
defective gene." Mainiero plans to work on the CRISPR Prime Editing
project, and Mazo-Molina will focus on understanding the molecular
mechanism of action underlying Ptr1.

Martin emphasizes that the collaboration between the Mainiero and
Mazo-Molina was key to the project's success. "It is a great example
of a collaboration within a lab between two different lab members,"
he says. "They worked seamlessly as a team."

========================================================================== Story Source: Materials provided by Boyce_Thompson_Institute. Original
written by Aaron J.

Bouchie. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Carolina Mazo‐Molina, Samantha Mainiero, Benjamin J. Haefner,
Ryland Bednarek, Jing Zhang, Ari Feder, Kai Shi, Susan R. Strickler,
Gregory B. Martin. Ptr1 evolved convergently with RPS2 and Mr5 to
mediate recognition of AvrRpt2 in diverse solanaceous species. The
Plant Journal, 2020; 103 (4): 1433 DOI: 10.1111/tpj.14810 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200902182419.htm

--- up 1 week, 2 days, 6 hours, 50 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1337:3/111)